Patent Publication Number: US-11658905-B2

Title: Routing control method, device, and system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/862,918, filed on Jan. 5, 2018, which is a continuation of International Application No. PCT/CN2015/083410, filed on Jul. 6, 2015. Both of the aforementioned applications are hereby incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     Embodiments of the application relate to the communications field, and in particular, to a routing control method, a device, and a system. 
     BACKGROUND 
     Generally, an autonomous system (AS) of an operator includes the following three types of devices: a provider edge (PE) device, a border router (BR), and a provider (P) device. The PE device is a network-side edge device of the autonomous system, is connected to a customer edge (CE) device, and is configured to access a user service. The BR is a border router of the autonomous system, and is configured to advertise a route between ASs. 
     The Border Gateway Protocol (BGP) is generally used for routing control between ASs of different operators. Different ASs are connected to each other by using a BR. When traffic needs to be adjusted and controlled (for example, some BRs or links are overloaded and congested, whereas some BRs or links are underloaded and idle), an operator generally needs to manually analyze traffic distribution and configure a routing policy, to adjust and control traffic flowing into and out of an AS managed by the operator. In addition, such manual configuration needs to be performed one by one on a related BR of the AS of the operator. This is laborious and time consuming. 
     SUMMARY 
     A routing control method and an apparatus provided in embodiments of the application help an operator to automatically adjust and control data traffic flowing into and out of an AS managed by the operator. 
     For this purpose, the embodiments of the application provide the following technical solutions. 
     According to a first aspect, a routing control method is provided, where the method includes receiving, by a controller, a first Border Gateway Protocol (BGP) routing message, where the controller is configured to manage a first autonomous system (AS), determining, by the controller according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control, if determining to perform incoming-traffic adjustment and control, determining, by the controller, a destination node according to the first BGP routing message, and allocating a source node from a second AS, where the destination node belongs to the first AS, and the second AS is at least one AS that is directly connected to the first AS, obtaining, by the controller, a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS, determining, by the controller, a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS, and sending, by the controller, a routing control message to a specified BR, where the specified BR belongs to the first AS, and the routing control message is used to instruct the specified BR to use, when advertising a second BGP routing message to the second AS, the first BR as a next hop for packet forwarding of the second BR. 
     With reference to the first aspect, in a first possible implementation of the first aspect, the determining, according to a node that sends the first BGP routing message to the controller, to perform incoming-traffic adjustment and control includes performing incoming-traffic adjustment and control if the controller determines that the node that sends the first BGP routing message to the controller is a border network device of the first AS, where the border network device of the first AS is a BR device or a provider edge (PE) device. 
     With reference to the first aspect, in a second possible implementation of the first aspect, the determining, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control includes searching, by the controller, a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     With reference to the first aspect, in a third possible implementation of the first aspect, the determining, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control includes obtaining, by the controller, a first destination prefix according to the first BGP routing message, and searching, by the controller, a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     With reference to any one of the first aspect, or the first to the third possible implementations of the first aspect, in a fourth possible implementation of the first aspect, the determining, by the controller, a destination node according to the first BGP routing message includes determining, by the controller, whether at least two first BGP routing messages are received, and if determining that at least two first BGP routing messages are received, setting, by the controller, a virtual node in the first AS, and determining the virtual node as the destination node, and correspondingly, the intra-domain topology further includes a link between the node that sends the first BGP routing message to the controller and the destination node. 
     With reference to any one of the first aspect, or the first to the third possible implementations of the first aspect, in a fifth possible implementation of the first aspect, the determining, by the controller, a destination node according to the first BGP routing message includes setting, by the controller, a virtual node in the first AS, and determining the virtual node as the destination node. Correspondingly, the intra-domain topology further includes a link between the border network device of the first AS and the destination node, and the obtaining, by the controller, a preferred path between the source node and the destination node by using a network topology includes obtaining, by the controller, a first affinity attribute constraint condition according to a link between the node that sends the first BGP routing message to the controller and the destination node, and obtaining, by the controller, the preferred path by using the network topology and the first affinity attribute constraint condition. 
     With reference to any one of the first aspect, or the first to the fifth possible implementations of the first aspect, in a sixth possible implementation of the first aspect, the allocating a source node from a second AS includes selecting, by the controller, one node from a border router or a virtual node in the second AS, as the source node. 
     With reference to any one of the first aspect, or the first to the fifth possible implementations of the first aspect, in a seventh possible implementation of the first aspect, the allocating a source node from a second AS includes searching, by the controller, a third configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node, or obtaining, by the controller, a first destination prefix according to the first BGP routing message, and searching, by the controller, a fourth configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     With reference to any one of the first aspect, or the first to the seventh possible implementations of the first aspect, in an eighth possible implementation of the first aspect, the source node is a BR that is in the second AS and that is directly connected to the first AS, and the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     With reference to any one of the first aspect, or the first to the seventh possible implementations of the first aspect, in a ninth possible implementation of the first aspect, the source node is a virtual node that is set in the second AS, and the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the source node and the BR of the second AS. 
     With reference to the eighth or the ninth possible implementation of the first aspect, in a tenth possible implementation of the first aspect, a manner in which the controller obtains the inter-domain topology is obtaining, by the controller, a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message, determining, by the controller, whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table, and if determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, establishing, by the controller according to the link identifier, the inter-domain topology between the first AS and an AS that is directly connected to the first AS. 
     With reference to any one of the first aspect, or the first to the tenth possible implementations of the first aspect, in an eleventh possible implementation of the first aspect, the routing control message includes a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and an operation manner, and the operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and the neighbor pair, and if the matching succeeds, not to perform an operation of increasing an AS quantity in an AS-path attribute value carried in the second BGP routing message, or if the matching fails, to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS. 
     With reference to the eleventh possible implementation of the first aspect, in a twelfth possible implementation of the first aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a reject value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries the identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path attribute value, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     With reference to any one of the first aspect, or the first to the tenth possible implementations of the first aspect, in a thirteenth possible implementation of the first aspect, the routing control message includes at least one neighbor pair and an operation manner, the at least one neighbor pair does not include a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and the operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and each of the at least one neighbor pair, and if the matching succeeds, to perform an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS. 
     With reference to the thirteenth possible implementation of the first aspect, in a fourteenth possible implementation of the first aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and at least one sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is greater than or equal to 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of a BR in the first AS, other than the identifier of the first BR, and the neighbor peer device identifier field carries an identifier of a BR in the second AS, other than the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path attribute value, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     According to a second aspect, a routing control method is provided, where the method includes receiving, by a specified border router BR in a first AS, a routing control message from a controller, where the routing control message is used to instruct the specified BR to use, when advertising a second BGP routing message to a second AS, a first BR as a next hop for packet forwarding of a second BR, the first BR belongs to the first AS, the second BR belongs to the second AS, and the controller is configured to manage the first autonomous system (AS), and processing, by the specified BR according to the routing control message, the second BGP routing message advertised to the second AS. 
     With reference to the second aspect, in a first possible implementation of the second aspect, the routing control message includes a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and an operation manner, and the operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and the neighbor pair, and if the matching succeeds, not to perform an operation of increasing an AS quantity in an AS-path attribute value carried in the second BGP routing message, or if the matching fails, to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS, and correspondingly, the processing, by the specified BR according to the routing control message, the BGP routing message advertised to the second AS includes performing matching, by the specified BR, between the identifier of the specified BR and the identifier of the destination BR and the neighbor pair when the specified BR advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, not performing the operation of increasing the AS quantity in the AS-path attribute value carried in the BGP routing message, or if the matching fails, performing the operation of increasing the AS quantity in the AS-path attribute value. 
     With reference to the first possible implementation of the second aspect, in a second possible implementation of the second aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a reject value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries the identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     With reference to the second aspect, in a third possible implementation of the second aspect, the routing control message includes at least one neighbor pair and an operation manner, the at least one neighbor pair does not include a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and the operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and each of the at least one neighbor pair, and if the matching succeeds, to perform an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS, and correspondingly, the processing, by the specified BR according to the routing control message, the BGP routing message advertised to the second AS includes performing matching, by the specified BR, between the identifier of the specified BR and the identifier of the destination BR and each of the at least one neighbor pair when the specified BR advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, performing the operation of increasing the AS quantity in the AS-path attribute value, or if the matching fails, not performing the operation of increasing the AS quantity in the AS-path attribute value. 
     With reference to the third possible implementation of the second aspect, in a fourth possible implementation of the second aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and at least one sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is greater than or equal to 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of a BR in the first AS, other than the identifier of the first BR, and the neighbor peer device identifier field carries an identifier of a BR in the second AS, other than the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     According to a third aspect, a controller is provided, where the controller is configured to manage a first autonomous system (AS), and the controller includes a communications unit, configured to receive a first Border Gateway Protocol (BGP) routing message, and a processing unit, configured to determine a destination node according to the first BGP routing message, where the destination node belongs to the first AS, where the processing unit is further configured to determine, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control, if determining to perform incoming-traffic adjustment and control, the processing unit is further configured to allocate a source node from a second AS, where the second AS is at least one AS that is directly connected to the first AS, the processing unit is further configured to obtain a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS, the processing unit is further configured to determine a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS, and the communications unit is further configured to send a routing control message to a specified BR, where the specified BR belongs to the first AS, and the routing control message is used to instruct the specified BR to use, when advertising a second BGP routing message to the second AS, the first BR as a next hop for packet forwarding of the second BR. 
     With reference to the third aspect, in a first possible implementation of the third aspect, the determining, according to a node that sends the first BGP routing message to the controller, to perform incoming-traffic adjustment and control includes performing, by the processing unit, incoming-traffic adjustment and control if determining that the node that sends the first BGP routing message to the controller is a border network device of the first AS, where the border network device of the first AS is a BR device or a provider edge PE device. 
     With reference to the third aspect, in a second possible implementation of the third aspect, the determining, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control includes searching, by the processing unit, a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     With reference to the third aspect, in a third possible implementation of the third aspect, the determining, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control includes obtaining, by the processing unit, a first destination prefix according to the first BGP routing message, and searching, by the processing unit, a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     With reference to any one of the third aspect, or the first to the third possible implementations of the third aspect, in a fourth possible implementation of the third aspect, the determining, by the processing unit, a destination node according to the first BGP routing message includes determining, by the processing unit, whether at least two first BGP routing messages are received, and if determining that at least two first BGP routing messages are received, setting, by the processing unit, a virtual node in the first AS, and determining the virtual node as the destination node, and correspondingly, the intra-domain topology further includes a link between the node that sends the first BGP routing message to the controller and the destination node. 
     With reference to any one of the third aspect, or the first to the third possible implementations of the third aspect, in a fifth possible implementation of the third aspect, the determining, by the processing unit, a destination node according to the first BGP routing message includes setting, by the processing unit, a virtual node in the first AS, and determining the virtual node as the destination node, correspondingly, the intra-domain topology further includes a link between the border network device of the first AS and the destination node, and the obtaining, by the processing unit, a preferred path between the source node and the destination node by using a network topology includes obtaining, by the processing unit, a first affinity attribute constraint condition according to a link between the node that sends the first BGP routing message to the controller and the destination node, and obtaining, by the controller, the preferred path by using the network topology and the first affinity attribute constraint condition. 
     With reference to any one of the third aspect, or the first to the fifth possible implementations of the third aspect, in a sixth possible implementation of the third aspect, the allocating a source node from a second AS includes determining, by the processing unit, one AS that is directly connected to the first AS, as the second AS, and allocating, by the processing unit, the source node from the second AS. 
     With reference to any one of the third aspect, or the first to the fifth possible implementations of the third aspect, in a seventh possible implementation of the third aspect, the allocating a source node from a second AS includes searching, by the processing unit, a third configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node, or obtaining, by the processing unit, a first destination prefix according to the first BGP routing message, and searching, by the processing unit, a fourth configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     With reference to any one of the third aspect, or the first to the seventh possible implementations of the third aspect, in an eighth possible implementation of the third aspect, the source node is a BR that is in the second AS and that is directly connected to the first AS, and the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     With reference to any one of the third aspect, or the first to the seventh possible implementations of the third aspect, in a ninth possible implementation of the third aspect, the source node is a virtual node that is set in the second AS, and the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the source node and the BR of the second AS. 
     With reference to the eighth or the ninth possible implementation of the third aspect, in a tenth possible implementation of the third aspect, a manner in which the processor obtains the inter-domain topology is obtaining, by the processing unit, a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message, determining, by the processing unit, whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table, and if determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, establishing, by the processing unit according to the link identifier, the inter-domain topology between the first AS and an AS that is directly connected to the first AS. 
     With reference to any one of the third aspect, or the first to the tenth possible implementations of the third aspect, in an eleventh possible implementation of the third aspect, the routing control message includes a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and an operation manner, and the operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and the neighbor pair, and if the matching succeeds, not to perform an operation of increasing an AS quantity in an AS-path attribute value carried in the second BGP routing message, or if the matching fails, to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS. 
     With reference to the eleventh possible implementation of the third aspect, in a twelfth possible implementation of the third aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a reject value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries the identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     With reference to any one of the third aspect, or the first to the tenth possible implementations of the third aspect, in a thirteenth possible implementation of the third aspect, the routing control message includes at least one neighbor pair and an operation manner, the at least one neighbor pair does not include a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and the operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and each of the at least one neighbor pair, and if the matching succeeds, to perform an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS. 
     With reference to the thirteenth possible implementation of the third aspect, in a fourteenth possible implementation of the third aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and at least one sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is greater than or equal to 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of a BR in the first AS, other than the identifier of the first BR, and the neighbor peer device identifier field carries an identifier of a BR in the second AS, other than the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     According to a fourth aspect, a border router is provided, where the border router is used as a specified border router BR, the specified BR belongs to a first autonomous system AS, and the specified BR includes a communications unit, configured to receive a routing control message from a controller, where the routing control message is used to instruct the specified BR to use, when advertising a BGP routing message to a second AS, a first BR as a next hop for packet forwarding of a second BR, the first BR belongs to the first AS, the second BR belongs to the second AS, and the controller is configured to manage the first AS, and a processing unit, configured to process, according to the routing control message, the BGP routing message advertised to the second AS. 
     With reference to the fourth aspect, in a first possible implementation of the fourth aspect, the routing control message includes a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and an operation manner, and the operation manner instructs the specified BR to perform matching, when advertising the BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and the neighbor pair, and if the matching succeeds, not to perform an operation of increasing an AS quantity in an AS-path attribute value carried in the BGP routing message, or if the matching fails, to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS, and correspondingly, the processing, by the processing unit according to the routing control message, the BGP routing message advertised to the second AS includes performing matching, by the processing unit, between the identifier of the specified BR and the identifier of the destination BR and the neighbor pair when the communications unit advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, not performing the operation of increasing the AS quantity in the AS-path attribute value carried in the BGP routing message, or if the matching fails, performing the operation of increasing the AS quantity in the AS-path attribute value, where the destination BR is the BR in the second AS. 
     With reference to the first possible implementation of the fourth aspect, in a second possible implementation of the fourth aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a reject value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries the identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     With reference to the fourth aspect, in a third possible implementation of the fourth aspect, the routing control message includes at least one neighbor pair and an operation manner, the at least one neighbor pair does not include a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and the operation manner instructs the specified BR to perform matching, when advertising the BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and each of the at least one neighbor pair, and if the matching succeeds, to perform an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not to perform an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS, and correspondingly, the processing, by the processing unit according to the routing control message, the BGP routing message advertised to the second AS includes performing matching, by the processing unit, between the identifier of the specified BR and the identifier of the destination BR and each of the at least one neighbor pair when the communications unit advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, performing the operation of increasing the AS quantity in the AS-path attribute value, or if the matching fails, not performing the operation of increasing the AS quantity in the AS-path attribute value, where the destination BR is the BR in the second AS. 
     With reference to the third possible implementation of the fourth aspect, in a fourth possible implementation of the fourth aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and at least one sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is greater than or equal to 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of a BR in the first AS, other than the identifier of the first BR, and the neighbor peer device identifier field carries an identifier of a BR in the second AS, other than the identifier of the second BR, and the action field includes an action type field, an action length field, and an action value field, where the action type field indicates to perform the operation of increasing the AS quantity in the AS-path, the action length field indicates a length of the action field or a length of the action value field, and the action value field carries the AS quantity. 
     According to a fifth aspect, a network system is provided, where the network system includes a controller and a border router BR, the controller is any controller according to the third aspect, and the BR is any specified BR according to the fourth aspect. 
     According to a sixth aspect, a routing control method is provided, where the method includes receiving, by a controller, a Border Gateway Protocol BGP routing message, where the controller is configured to manage a first autonomous system AS, determining, by the controller according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control, if determining to perform outgoing-traffic adjustment and control, determining, by the controller, a destination node according to the BGP routing message, and allocating a source node from the first AS, where the destination node belongs to a second AS, and the second AS is at least one AS that is directly connected to the first AS, obtaining, by the controller, a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS, determining, by the controller, a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS, and sending, by the controller, a routing control message to the first BR, where the routing control message is used to instruct the first BR to use the second BR as a next hop for packet forwarding. 
     With reference to the sixth aspect, in a first possible implementation of the sixth aspect, the determining, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control includes performing outgoing-traffic adjustment and control if the controller determines that the node that sends the BGP routing message to the controller is a BR of the first AS. 
     With reference to the sixth aspect, in a second possible implementation of the sixth aspect, the determining, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control includes searching, by the controller, a first configuration information table by using the node that sends the BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     With reference to the sixth aspect, in a third possible implementation of the sixth aspect, the determining, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control includes obtaining, by the controller, a first destination prefix according to the BGP routing message, and searching, by the controller, a second configuration information table by using the node that sends the BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     With reference to any one of the sixth aspect, or the first to the third possible implementations of the sixth aspect, in a fourth possible implementation of the sixth aspect, the allocating a source node from the first AS includes searching, by the controller, a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node, or obtaining, by the controller, a first destination prefix according to the first BGP routing message, and searching, by the controller, a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     With reference to any one of the sixth aspect, or the first to the fourth possible implementations of the sixth aspect, in a fifth possible implementation of the sixth aspect, the destination node is a BR in the second AS, and the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     With reference to any one of the sixth aspect, or the first to the fourth possible implementations of the sixth aspect, in a sixth possible implementation of the sixth aspect, the destination node is a virtual node that is set in the second AS, and the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the destination node and the BR of the second AS. 
     With reference to the fifth or the sixth possible implementation of the sixth aspect, in a seventh possible implementation of the sixth aspect, a manner in which the controller obtains the inter-domain topology is establishing, by the controller, a link between a BR that is identified by a next-hop field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the next-hop field belongs to the second AS, or establishing, by the controller, a link between a BR that is identified by a community attribute field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the community attribute field belongs to the second AS. 
     With reference to the fifth or the sixth possible implementation of the sixth aspect, in an eighth possible implementation of the sixth aspect, a manner in which the controller obtains the inter-domain topology is obtaining, by the controller, a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message, determining, by the controller, whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table, and if determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, establishing, by the controller, the inter-domain topology between the first AS and the second AS according to the link identifier, and correspondingly, the obtaining, by the controller, a preferred path between the source node and the destination node by using a network topology includes obtaining, by the controller, an affinity attribute constraint condition according to a link between the node that sends the BGP routing message to the controller and the BR of the second AS, and obtaining, by the controller, the preferred path by using the network topology and the affinity attribute constraint condition. 
     With reference to any one of the sixth aspect, or the first to the eighth possible implementations of the sixth aspect, in a ninth possible implementation of the sixth aspect, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from the BGP routing message. 
     With reference to the ninth possible implementation of the sixth aspect, in a tenth possible implementation of the sixth aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, the action field includes an action type field and an action length field, where the action type field indicates to perform a preferred-routing operation, and the action length field indicates a length of the action field or a length of the action value field, and the BGP policy attribute instructs the first BR to perform matching between the identifier of the first BR and the neighbor local device identifier field in the neighbor pair field, and if the matching succeeds, to perform an operation of using the second BR as the next hop for routing to the destination prefix. 
     According to a seventh aspect, a routing control method is provided, where the method includes receiving, by a first border router BR in a first AS, a routing control message from a controller, where the routing control message is used to instruct the first BR to use a second BR as a next hop for packet forwarding, and the second BR belongs to a second AS, and determining, by the first BR according to the routing control message, the second BR as the next hop for packet forwarding. 
     With reference to the seventh aspect, in a first possible implementation of the seventh aspect, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from a BGP routing message. 
     With reference to the first possible implementation of the seventh aspect, in a second possible implementation of the seventh aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, the action field includes an action type field and an action length field, where the action type field indicates to perform a preferred-routing operation, and the action length field indicates a length of the action field or a length of the action value field, and the BGP policy attribute instructs the first BR to perform matching between the identifier of the first BR and the neighbor local device identifier field in the neighbor pair field, and if the matching succeeds, to perform an operation of using the second BR as the next hop for routing to the destination prefix. 
     According to an eighth aspect, a controller is provided, where the controller is configured to manage a first autonomous system AS, and the controller includes a communications unit, configured to receive a Border Gateway Protocol BGP routing message, and a processing unit, configured to determine, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control, where if determining to perform outgoing-traffic adjustment and control, the processing unit is further configured to determine a destination node according to the BGP routing message, and allocate a source node from the first AS, where the destination node belongs to a second AS, and the second AS is at least one AS that is directly connected to the first AS, the processing unit is further configured to obtain a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS, the processing unit is further configured to determine a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS, and the processing unit is further configured to send a routing control message to the first BR, where the routing control message is used to instruct the first BR to use the second BR as a next hop for packet forwarding. 
     With reference to the eighth aspect, in a first possible implementation of the eighth aspect, the determining, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control includes the processing unit is further configured to perform outgoing-traffic adjustment and control if determining that the node that sends the BGP routing message to the controller is a BR of the first AS. 
     With reference to the first possible implementation of the eighth aspect, in a second possible implementation of the eighth aspect, the determining, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control includes the processing unit is further configured to search a first configuration information table by using the node that sends the BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     With reference to the first possible implementation of the eighth aspect, in a third possible implementation of the eighth aspect, the determining, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control includes the processing unit is further configured to obtain a first destination prefix according to the BGP routing message, and the processing unit is further configured to search a second configuration information table by using the node that sends the BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     With reference to any one of the eighth aspect, or the first to the third possible implementations of the eighth aspect, in a fourth possible implementation of the eighth aspect, the allocating a source node from the first AS includes the processing unit is further configured to search a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node, or, obtaining, by the processing unit, a first destination prefix according to the first BGP routing message, and searching, by the processing unit, a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     With reference to any one of the eighth aspect, or the first to the fourth possible implementations of the eighth aspect, in a fifth possible implementation of the eighth aspect, the destination node is a BR in the second AS, and the inter-domain topology between the BRs of the first AS and the second AS includes, an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     With reference to any one of the eighth aspect, or the first to the fourth possible implementations of the eighth aspect, in a sixth possible implementation of the eighth aspect, the destination node is a virtual node that is set in the second AS, and the inter-domain topology between the BRs of the first AS and the second AS includes, an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the destination node and the BR of the second AS. 
     With reference to the fifth or the sixth possible implementation of the eighth aspect, in a seventh possible implementation of the eighth aspect, a manner in which the controller obtains the inter-domain topology is the processing unit is further configured to establish a link between a BR that is identified by a next-hop field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the next-hop field belongs to the second AS, or the processing unit is further configured to establish a link between a BR that is identified by a community attribute field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the community attribute field belongs to the second AS. 
     With reference to any one of the eighth aspect, or the first to the fourth possible implementations of the eighth aspect, in an eighth possible implementation of the eighth aspect, a manner in which the controller obtains the inter-domain topology is the processing unit is further configured to obtain a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message, the processing unit is further configured to determine whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table, and if determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, the processing unit is further configured to establish the inter-domain topology between the first AS and the second AS according to the link identifier, and correspondingly, that the processing unit is further configured to obtain a preferred path between the source node and the destination node by using a network topology includes obtaining, by the processing unit, an affinity attribute constraint condition according to a link between the node that sends the BGP routing message to the controller and the BR of the second AS, and obtaining, by the processing unit, the preferred path by using the network topology and the affinity attribute constraint condition. 
     With reference to any one of the eighth aspect, or the first to the eighth possible implementations of the eighth aspect, in a ninth possible implementation of the eighth aspect, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from the BGP routing message. 
     With reference to the ninth possible implementation of the eighth aspect, in a tenth possible implementation of the eighth aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, the action field includes an action type field and an action length field, where the action type field indicates to perform a preferred-routing operation, and the action length field indicates a length of the action field or a length of the action value field, and the BGP policy attribute instructs the first BR to perform matching between the identifier of the first BR and the neighbor local device identifier field in the neighbor pair field, and if the matching succeeds, to perform an operation of using the second BR as the next hop for routing to the destination prefix. 
     According to a ninth aspect, a border router is provided, where the border router is used as a first border router BR, the first BR belongs to a first autonomous system AS, and the first BR includes a communications unit, configured to receive a routing control message from a controller, where the routing control message is used to instruct the first BR to use a second BR as a next hop for packet forwarding, and the second BR belongs to a second AS, and a processing unit, configured to determine, according to the routing control message, the second BR as the next hop for packet forwarding. 
     With reference to the ninth aspect, in a first possible implementation of the ninth aspect, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from a BGP routing message, and correspondingly, the processing unit sets the next hop for routing to the destination prefix to the second BR. 
     With reference to the first possible implementation of the ninth aspect, in a second possible implementation of the ninth aspect, the routing control message is an extended BGP update update message, the extended BGP update message includes a BGP policy attribute, and the BGP policy attribute includes a match field and an action field, where the match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field, where the match type field carries a permit value, the sub-type length value sub-TLV quantity field indicates that a quantity of sub-TLVs carried in the match field is 1, the sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field, the sub-type sub-type field indicates that a type of the sub-value field is a neighbor pair and an IP address type of the neighbor pair, the sub-length field indicates a length of the sub-TLV or a length of the sub-value field, the sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field, the neighbor local device identifier field carries an identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR, the action field includes an action type field and an action length field, where the action type field indicates to perform a preferred-routing operation, and the action length field indicates a length of the action field or a length of the action value field, and the BGP policy attribute instructs the first BR to perform matching between the identifier of the first BR and the neighbor local device identifier field in the neighbor pair field, and if the matching succeeds, to perform an operation of using the second BR as the next hop for routing to the destination prefix. 
     According to a tenth aspect, a network system is provided, where the network system includes a controller and a border router BR, the controller is any controller according to the eighth aspect, and the BR is any BR according to the ninth aspect. 
     According to the routing control method, the apparatus, and the system provided in the embodiments of the application, the controller receives the BGP routing message, where the controller is configured to manage the first autonomous system AS, the controller determines, according to the node that sends the first BGP routing message to the controller, whether to perform incoming-traffic or outgoing-traffic adjustment and control, if determining to perform incoming-traffic adjustment and control, the controller determines the destination node according to the first BGP routing message, and allocates the source node from the second AS, where the destination node belongs to the first AS, and the second AS is at least one AS that is directly connected to the first AS, or if determining to perform outgoing-traffic adjustment and control, the controller determines the destination node according to the BGP routing message, and allocates the source node from the first AS, where the destination node belongs to the second AS, and the second AS is at least one AS that is directly connected to the first AS, the controller obtains the preferred path between the source node and the destination node by using the network topology, where the network topology includes the intra-domain topology of the first AS and the inter-domain topology between the BRs of the first AS and the second AS, the controller determines the first BR and the second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS, and the controller sends the routing control message to the BR, to control the BR to forward, according to the preferred path, data traffic flowing into and out of the first AS. This helps an operator to automatically adjust and control data traffic flowing into and out of an AS managed by the operator. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To describe the technical solutions in the application more clearly, the following briefly describes the accompanying drawings used in the embodiments. Apparently, the accompanying drawings in the following descriptions show merely some embodiments of the application, and persons of ordinary skill in the art may still derive other technical solutions and drawings that can also implement the application, from these accompanying drawings without creative efforts. These technical solutions and drawings shall also be considered as falling within the scope of the application. 
         FIG.  1    is a schematic network diagram according to an embodiment of the application; 
         FIG.  2    is a simplified schematic diagram of a routing control method on a controller side according to an embodiment of the application; 
         FIG.  3   a    is a schematic network diagram of incoming-traffic control according to an embodiment of the application; 
         FIG.  3   b    is another schematic network diagram of incoming-traffic control according to an embodiment of the application; 
         FIG.  4   a    shows a coding format of a BGP policy attribute according to an embodiment of the application; 
         FIG.  4   b    shows another coding format of a BGP policy attribute according to an embodiment of the application; 
         FIG.  5    is a simplified schematic diagram of a routing control method on a border router side according to an embodiment of the application; 
         FIG.  6    is a schematic structural diagram of a controller according to an embodiment of the application; 
         FIG.  7    is a schematic structural diagram of a controller according to an embodiment of the application; 
         FIG.  8    is a schematic structural diagram of a border router according to an embodiment of the application; 
         FIG.  9    is a schematic structural diagram of a border router according to an embodiment of the application; 
         FIG.  10    is a simplified schematic diagram of a routing control method on a controller side according to an embodiment of the application; 
         FIG.  11   a    and  FIG.  11   b    are schematic network diagrams of outgoing-traffic control according to an embodiment of the application; 
         FIG.  12    is a schematic diagram of a BGP policy attribute according to an embodiment of the application; 
         FIG.  13    is a simplified schematic diagram of a routing control method on a border router side according to an embodiment of the application; 
         FIG.  14    is a schematic structural diagram of a controller according to an embodiment of the application; 
         FIG.  15    is a schematic structural diagram of a controller according to an embodiment of the application; 
         FIG.  16    is a schematic structural diagram of a border router according to an embodiment of the application; 
         FIG.  17    is a schematic structural diagram of a border router according to an embodiment of the application; 
         FIG.  18    is a schematic diagram of a network system according to an embodiment of the application; and 
         FIG.  19    is a schematic diagram of another network system according to an embodiment of the application. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     To make persons skilled in the art better understand the solutions in the application, the following further describes the embodiments of the application in detail with reference to the accompanying drawings and implementations. 
     Before the technical solutions in the embodiments of the application are described, a specific application scenario of the embodiments of the application is briefly described first. 
     Referring to  FIG.  1   ,  FIG.  1    shows a scenario of a network architecture that is based on control-forwarding separation. A controller manages a network device in a first autonomous system AS 1 . The network device includes a border router and a PE device. Specifically, the controller controls border routers BR 100 - 1 , BR 100 - 2 , and BR 100 - 3 , a PE device  110 - 1 , and a PE device  110 - 2  in the AS 1  by using a control channel protocol. A BR 200 - 1  and a BR 200 - 2  are border routers located in a second autonomous system AS 2 . A BR between the AS 1  and the AS 2  performs routing control by using a routing message defined by the BGP protocol. Specifically, the routing message may be a BGP update update message. For example, the routing message may include at least the following fields: a network prefix, a multi-exit discriminator (MED), a next hop (NH), an autonomous system path (AS PATH), and a local preference. The prefix field is used to carry a destination reachable address that may be an IP address or a network segment address. The MED field is used to carry a MED value. Based on an existing route selection policy, an IGW with a smallest MED value may be selected as an optimal route. The NH field is used to carry an identifier of a next hop in packet forwarding. For example, the identifier of the next hop may be an IP address, a device identity, a device port identifier, or the like. The AS path field is used to carry a number of an AS that is passed through during packet forwarding. Based on the existing route selection policy, a BR with a shortest AS path may be selected as an optimal route. That an AS path is the shortest may be understood as that a quantity of AS numbers included in the AS path is the smallest. The local preference field is used to carry a local preference value. Based on the existing route selection policy, a BR with a largest local preference value may be selected as an optimal route. 
     Outgoing data traffic and incoming data traffic shown in  FIG.  1    are specific to the AS 1 . The outgoing data traffic (simply referred to as outgoing traffic) means traffic flowing out of the AS 1 , and the incoming data traffic (simply referred to as incoming traffic) means traffic flowing into the AS 1 . Both the outgoing traffic and the incoming traffic are service data traffic. 
     It should be noted that, first, the AS 2  in this embodiment represents an AS that is directly connected to the AS 1 . Specifically, the AS 2  may include one or more or all of ASs that are directly connected to the AS 1 . No specific limitation is imposed herein. 
     Secondly, the AS 1  in this embodiment may further include a provider P device. 
     Thirdly, the PE and BR in this embodiment may be collectively referred to as a border network device in one AS, and may be routers, switches, or other network forwarding devices. 
     Lastly, the controller may be an independent device. Alternatively, the controller may be a route reflector (RR), a PE, a BR, or a P device into which a controller function is integrated. Alternatively, a function of the controller may be implemented by multiple different devices together, that is, the function of the controller is divided and distributed to the multiple different devices, so as to implement the function of the controller in a distributed manner. This embodiment of the application does not impose any specific limitation on a form of the controller in a network. 
     The embodiments of the application provide a routing control method, so as to automatically and flexibly adjust and control a forwarding path through which data traffic flows into and out of an AS. The following provides descriptions from two aspects: incoming traffic and outgoing traffic. 
     1. Incoming-Traffic Routing Control Method, Apparatus, and System 
     The incoming-traffic routing control method in the embodiments of the application includes processing on a controller side and a border router side. The following provides descriptions separately. 
       FIG.  2    is a simplified flowchart of a routing control method on a controller side according to an embodiment of the application. If the method is applied to a network scenario similar to that shown in  FIG.  1   , the method includes the operations described below. It should be noted that the method shown in  FIG.  2    not only can be applied to a network structure shown in  FIG.  1   , but also can be applied to another type of network system, for example, a network system constituted by a network device that does not use any replaceable component. 
       201 : A controller receives a first Border Gateway Protocol BGP routing message, where the controller is configured to manage a first autonomous system AS. 
       202 : The controller determines, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control. 
     Optionally, there may be the following several manners in which the controller determines to perform incoming-traffic adjustment and control. 
     Manner 1: The controller performs incoming-traffic adjustment and control if the controller determines that the node that sends the first BGP routing message to the controller is a border network device of the first AS. The border network device of the first AS is a BR device or a provider edge (PE) device. 
     With reference to an example shown in  FIG.  1   , the node that sends the first BGP routing message to the controller may be the PE device  110 - 1 , the PE device  110 - 2 , the border router BR 100 - 3 , the border router BR 100 - 1 , or the border router BR 100 - 2 . All these devices are border network devices of the AS 1 . When receiving the first BGP routing message sent from these border network devices of the AS 1 , the controller  130  determines to perform incoming-traffic adjustment and control. This is a random adjustment and control manner. 
     Manner 2: The controller searches a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller is the PE device  110 - 1 , the controller  130  searches, by using an identifier of the PE device  110 - 1  as a match item, a configuration information table shown in Table 1, to obtain an operation manner that is incoming-traffic adjustment and control. This is a type of coarse-grained traffic adjustment and control for a node. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
               
            
               
                   
                 Match item 
                 Operation manner 
               
               
                   
                   
               
               
                   
                 Identifier of the 
                 Incoming-traffic 
               
               
                   
                 PE device 110-1 
                 adjustment and control 
               
               
                   
                 Identifier of the 
                 Incoming-traffic 
               
               
                   
                 PE device 110-2 
                 adjustment and control 
               
               
                   
                 Identifier of the 
                 Incoming-traffic 
               
               
                   
                 border router BR100-3 
                 adjustment and control 
               
               
                   
                   
               
            
           
         
       
     
     Manner 3: The controller obtains a first destination prefix according to the first BGP routing message. 
     The controller searches a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller  130  is the PE device  110 - 1 , and a destination prefix obtained by the controller  130  from the first BGP routing message is a prefix 1 (for example, an IP address prefix 10.1.0.0/16 or an IP address 10.1.1.1/32, the prefix 1 is a routing destination prefix in a network, and is further used to identify a virtual node  120 - 1  in this embodiment of the application), the controller  130  searches, by using an identifier (which may be, for example, an IP address) of the PE device  110 - 1  and the prefix 1 as a match item, a configuration information table shown in Table 2, to obtain an operation manner that is incoming-traffic adjustment and control. This is a type of fine-grained traffic adjustment and control for a node and a prefix. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
            
               
                 Match item 
                   
               
            
           
           
               
               
               
            
               
                 Device identifier 
                 Destination prefix 
                 Operation manner 
               
               
                   
               
               
                 Identifier of the 
                 Prefix 1 
                 Incoming-traffic 
               
               
                 PE device 110-1 
                   
                 adjustment and control 
               
               
                 Identifier of the 
                 Prefix 2 
                 Incoming-traffic 
               
               
                 PE device 110-2 
                   
                 adjustment and control 
               
               
                 Identifier of the 
                 Prefix 3 
                 Incoming-traffic 
               
               
                 border router BR100-3 
                   
                 adjustment and control 
               
               
                   
               
            
           
         
       
     
       203 : If determining to perform incoming-traffic adjustment and control, the controller determines a destination node according to the first BGP routing message, and allocates a source node from a second AS, where the destination node belongs to the first AS, and the second AS is at least one AS that is directly connected to the first AS. 
     Optionally, there may be the following several manners in which the controller determines the destination node. 
     Manner 1: The controller determines whether at least two first BGP routing messages are received. 
     If determining that at least two first BGP routing messages are received, the controller sets a virtual node in the first AS, and determines the virtual node as the destination node. 
     Correspondingly, an intra-domain topology further includes a link between the node that sends the first BGP routing message to the controller and the destination node. 
     With reference to the example in  FIG.  1   , if the controller  130  determines that two first BGP routing messages are received from the PE device  110 - 1  and the PE device  110 - 2  respectively, the controller sets the virtual node  120 - 1  (for example, the prefix 1 may be used to identify the node) in the AS 1 , adds a virtual link between the virtual node  120 - 1  and the PE device  110 - 1 , and adds a virtual link between the virtual node  120 - 1  and the PE device  110 - 2 . 
     Manner 2: The controller sets a virtual node in the first AS, and determines the virtual node as the destination node. 
     Correspondingly, an intra-domain topology further includes a virtual link between a border network device of the first AS and the destination node, and obtaining, by the controller, a preferred path between the source node and the destination node by using a network topology includes: obtaining, by the controller, a first affinity attribute constraint condition according to a link between the node that sends the first BGP routing message to the controller and the destination node, and obtaining, by the controller, the preferred path by using the network topology and the first affinity attribute constraint condition. 
     With reference to an example in  FIG.  3   a   , the controller  130  sets the virtual node  120 - 1  as the destination node, and the intra-domain topology further includes a virtual link between the BR 100 - 3  of the AS 1  and the virtual node  120 - 1 . For example, the node that sends the first BGP routing message to the controller is the BR 100 - 3 . The controller  130  adds, for the incoming traffic, a first affinity attribute to the virtual link between the BR 100 - 3  and the virtual node  120 - 1 . The controller  130  obtains the preferred path between the source node (the BR 200 - 2 ) and the destination node (the virtual node  120 - 1 ) by using the network topology and the first affinity attribute constraint condition. 
     Manner 3: The controller may alternatively determine the node that sends the first BGP routing message to the controller, as the destination node. 
     With reference to the example in  FIG.  1   , the controller  130  is likely to determine, according to different service traffic, the destination node from the following nodes: the PE device  110 - 1 , the PE device  110 - 2 , the border router BR 100 - 3 , the border router BR 100 - 1 , and the border router BR 100 - 2 . 
     Optionally, there may be the following several manners in which the controller allocates the source node. 
     Manner 1: The controller selects one node from a border router or a virtual node in the second AS, as the source node. It should be noted that the controller may alternatively select one node from a P device or a PE device in the second AS, as the source node. 
     With reference to the example in  FIG.  1   , the controller  130  selects one BR from the border routers BRs in the AS 2 , as the source node. For example, the BR 200 - 2  is selected as the source node. 
     Manner 2: The controller searches a third configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller is the PE device  110 - 1 , the controller  130  searches, by using the identifier of the PE device  110 - 1  as a match item, a configuration information table shown in Table 3, to obtain a source node that is the BR 200 - 2 . 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
               
            
               
                   
                 Match item 
                 Source node 
               
               
                   
                   
               
               
                   
                 Identifier of the 
                 Identifier of the 
               
               
                   
                 PE device 110-1 
                 border router BR200-2 
               
               
                   
                 Identifier of the 
                 Identifier of the 
               
               
                   
                 PE device 110-2 
                 border router BR200-1 
               
               
                   
                 Identifier of the 
                 Identifier of the 
               
               
                   
                 border router BR100-3 
                 border router BR200-2 
               
               
                   
                   
               
            
           
         
       
     
     Manner 3: The controller obtains a first destination prefix according to the first BGP routing message. 
     The controller searches a fourth configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller  130  is the PE device  110 - 1 , and a destination prefix obtained by the controller  130  from the first BGP routing message is the prefix 1 (for example, the IP address prefix 10.1.0.0/16 or the IP address 10.1.1.1/32, the prefix 1 is a routing destination prefix in a network, and is further used to identify the virtual node  120 - 1  in this embodiment of the application), the controller  130  searches, by using the identifier (which may be, for example, the IP address) of the PE device  110 - 1  and the prefix 1 as a match item, a configuration information table shown in Table 4, to obtain a source node that is the BR 200 - 2 . 
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
            
               
                 Match item 
                   
               
            
           
           
               
               
               
            
               
                 Device identifier 
                 Destination prefix 
                 Source node 
               
               
                   
               
               
                 Identifier of the 
                 Prefix 1 
                 Identifier of the 
               
               
                 PE device 110-1 
                   
                 border router BR200-2 
               
               
                 Identifier of the 
                 Prefix 2 
                 Identifier of the 
               
               
                 PE device 110-2 
                   
                 border router BR200-1 
               
               
                 Identifier of the 
                 Prefix 3 
                 Identifier of the 
               
               
                 border router BR100-3 
                   
                 border router BR200-2 
               
               
                   
               
            
           
         
       
     
       204 : The controller obtains the preferred path between the source node and the destination node by using the network topology, where the network topology includes the intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS. 
     The intra-domain topology of the first AS may include the following several cases. 
     Case 1: The intra-domain topology of the first AS includes at least one BR of the first AS and/or a link that connects BRs of the first AS. 
     Case 2: The intra-domain topology of the first AS includes at least one BR of the first AS, at least one provider edge PE device, and a link that connects these devices. 
     Case 3: The intra-domain topology of the first AS includes at least one BR of the first AS, at least one provider edge PE device, at least one P device, and a link that connects these devices. 
     Case 4: The intra-domain topology of the first AS includes at least one BR of the first AS, at least one provider P device, and a link that connects these devices. 
     The inter-domain topology between the BRs of the first AS and the second AS may include two cases. 
     Case 1: When the source node is a BR that is in the second AS and that is directly connected to the first AS, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     With reference to the example in  FIG.  1   , the inter-domain topology includes the BR 200 - 1 , the BR 200 - 2 , the BR 100 - 1 , the BR 100 - 2 , and a link that connects these nodes. 
     Case 2: When the source node is a virtual node that is set in the second AS, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the source node and the BR of the second AS. 
     With reference to the example in  FIG.  1   , the inter-domain topology includes the BR 200 - 1 , the BR 200 - 2 , the BR 100 - 1 , the BR 100 - 2 , and a link that connects these nodes. The inter-domain topology further includes a virtual node  210 - 1 , a virtual link between the virtual node  210 - 1  and the BR 200 - 1 , and a virtual link between the virtual node  210 - 1  and the BR 200 - 2 . 
     Optionally, a manner in which the controller obtains the inter-domain topology is obtaining, by the controller, a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message, determining, by the controller, whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table, and if determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, establishing, by the controller according to the link identifier, the inter-domain topology between the first AS and an AS that is directly connected to the first AS. 
     With reference to the example in  FIG.  1   , the preferred path is a preferred path of incoming data traffic from the BR 200 - 2 , through the BR 100 - 1  and the PE device  110 - 1 , to the virtual node  120 - 1 . 
     It should be noted that there may also be a P device in an AS 1  domain. In a possible scenario, the P device in the AS 1  domain may also be included on the preferred path. 
     With reference to an example in  FIG.  3   b   , the preferred path is a preferred path of incoming data traffic in an inter-domain topology from the BR 200 - 2  to the BR 100 - 1 . In this case, the BR 100 - 1  may be used as a border router of the AS 1 , or may be a network device that has both a border router function and a PE function. 
       205 : The controller determines a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS. 
     With reference to the example in  FIG.  1   , the first BR is the BR 100 - 1 , and the second BR is the BR 200 - 1 . 
       206 : The controller sends a routing control message to a specified BR, where the specified BR belongs to the first AS, and the routing control message is used to instruct the specified BR to use, when advertising a second BGP routing message to the second AS, the first BR as a next hop for packet forwarding of the second BR. 
     Optionally, the controller sends the routing control message to at least one border router of the first AS. Optionally, this includes sending the routing control message to all border routers of the first AS. 
     Optionally, the routing control message may have multiple specific forms, and may be an extended BGP update message. Specifically, the routing control message may alternatively be a BGP flow specification (FLOWSPEC) message, or may be an extended OpenFlow OpenFlow protocol of software-defined networking (SDN). The routing control message has two control manners. 
     Manner 1: The routing control message includes a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and an operation manner. The operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and the neighbor pair, and if the matching succeeds, not to perform an operation of increasing an AS quantity in an AS-path attribute value carried in the second BGP routing message, or if the matching fails, to perform an operation of increasing an AS quantity in an AS-path attribute value. The destination BR is a BR in the second AS. 
     Taking the extended BGP update message for example, the function may be implemented by extending a new BGP policy attribute. For definitions about the BGP update message and a related attribute, refer to the Request for Comments (RFC) 4271 standard defined by the Internet Engineering Task Force (IETF). For a definition about the BGP FLOWSPEC message, refer to the RFC5575. Details are not described herein. As shown in  FIG.  4   a   , a newly extended BGP policy attribute in this embodiment includes a match field and an action field. 
     The match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field. A possible value of the match type field is 0 (indicating permission) or 1 (indicating rejection). With reference to the example of incoming-traffic adjustment and control in  FIG.  1   , a value of the match type field is 1, indicating rejection. 
     The sub-type length value sub-TLV quantity field indicates a quantity of sub-TLVs carried in the match field, and a value of the sub-type length value sub-TLV quantity field may be a positive integer greater than or equal to 0. With reference to the example of incoming-traffic adjustment and control in  FIG.  1   , the value of the sub-TLV quantity field is 1. 
     The sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field. The sub-type sub-type field is used to identify a type of a neighbor pair, and may be an Internet Protocol version 4 (IPv4) address or an IPv6 address. A possible value of the sub-type field is as follows: sub-type=1, instructing to match an IPv4 neighbor pair, that is, a neighbor pair in which each device identifier is identified by using an IPv4 address, or sub-type=2, instructing to match an IPv6 neighbor pair, that is, a neighbor pair in which each device identifier is identified by using an IPv6 address. 
     The sub-length field indicates a length of the sub-TLV or a length of the sub-value field. The sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field. For example, a length of the neighbor local device identifier field may be 4 bytes or 16 bytes, and a length of the neighbor peer device identifier field may be 4 bytes or 16 bytes. With reference to the example of incoming-traffic adjustment and control in  FIG.  1   , the neighbor local device identifier field carries the identifier of the first BR, and the neighbor peer device identifier field carries the identifier of the second BR. 
     The action field includes an action type field, an action length field, and an action value field. A possible value of the action type (Action Type) field includes but is not limited to the following, including action type=1, instructing to perform a preferred-routing operation, where a length of the action type field may be 2 bytes, or action type=2, instructing to perform an operation of increasing an AS-path (AS-path) length, where a length of the action type field may be 2 bytes. 
     With reference to the example of incoming-traffic adjustment and control in  FIG.  1   , action type=2, instructing to perform the operation of increasing the AS quantity in the AS-path. 
     The action length field indicates a length of the action field or a length of the action value field. The action value field carries the AS quantity. 
     Manner 2: The routing control message includes at least one neighbor pair and an operation manner. The at least one neighbor pair does not include a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR. The operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and each of the at least one neighbor pair, and if the matching succeeds, to perform an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not to perform an operation of increasing an AS quantity in an AS-path attribute value. The destination BR is a BR in the second AS. 
     Taking the extended BGP update message for example, the function may be implemented by extending a new BGP policy attribute. A format of a newly added BGP policy attribute herein may be the same as a format shown in  FIG.  4   a   , except that field values are different in different usage scenarios. The format description is not described again. 
     As shown in  FIG.  4   b   , with reference to the example of incoming-traffic adjustment and control in  FIG.  1   , a value of the match type field is 0, indicating permission. A value of the sub-type length value sub-TLV quantity field is a positive integer greater than or equal to 1. This indicates that one or more sub-TLVs are included, and also means that one or more neighbor pairs are included. 
     A sub-value field in each sub-TLV includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field. The neighbor local device identifier field carries an identifier of a BR in the first AS, other than the identifier of the first BR. The neighbor peer device identifier field carries an identifier of a BR in the second AS, other than the identifier of the second BR. 
     Incoming-traffic adjustment and control in  FIG.  1    is used as an example. A neighbor pair included in a sub-TLV  1  is (BR 100 - 1 , BR 200 - 1 ), a neighbor pair included in a sub-TLV  2  is (BR 100 - 1 , BR 200 - 2 ), a neighbor pair included in a sub-TLV  3  is (BR 100 - 2 , BR 200 - 1 ), and a neighbor pair included in a sub-TLV  4  is (BR 100 - 2 , BR 200 - 2 ). 
     It should be noted that multiple formats may be used for a control packet in the embodiment shown in  FIG.  2   .  FIG.  4   a    and  FIG.  4   b    are two specific examples of the formats, and a value and a length of each field in the formats are also merely examples. 
     It should be noted that Table 1 to Table 4 in the embodiment shown in  FIG.  2    are merely examples. A specific implementation may alternatively be Table 1 and Table 3 are combined into one table for implementation, and Table 2 and Table 4 are combined into one table for implementation. An application described herein is not limited to a disclosed specific form. Instead, this disclosure covers all modifications, equivalents, and replacements falling within the scope of the accompanying claims. 
     It can be learned from the foregoing embodiment that, according to the solution in this embodiment, the controller receives the first BGP routing message, then automatically determines to perform incoming-traffic control, calculates the preferred path from the source node to the destination node, obtains the first BR and the second BR on the preferred path, sends the routing control message to the BR in the AS 1  controlled by the controller, and instructs the BR to use, when advertising the second BGP routing message to the second AS, the first BR as the next hop for packet forwarding of the second BR. Therefore, compared with a prior-art method in which configuration is manually performed one by one, this method facilitates automatic and flexible adjustment and control of data traffic flowing into an AS, simplifies configuration, and saves human power. 
       FIG.  5    is a simplified flowchart of a routing control method on a border router side according to an embodiment of the application. If the method is applied to a network scenario similar to that shown in  FIG.  1   , the method includes the operations described below. It should be noted that the method shown in  FIG.  5    not only can be applied to a network structure shown in  FIG.  1   , but also can be applied to another type of network system, for example, a network system constituted by a network device that does not use any replaceable component. 
       501 : A specified border router BR in a first AS receives a routing control message from a controller, where the routing control message is used to instruct the specified BR to use, when advertising a second BGP routing message to a second AS, a first BR as a next hop for packet forwarding of a second BR, the first BR belongs to the first AS, the second BR belongs to the second AS, and the controller is configured to manage the first autonomous system AS. 
       502 : The specified BR processes, according to the routing control message, the second BGP routing message advertised to the second AS. 
     It should be noted that the embodiment shown in  FIG.  5    is corresponding to the routing control method on the controller side. Descriptions of related content such as the routing control message are the same as those in the embodiment shown in  FIG.  2   , and details are not described herein again. 
     Optionally, the routing control message has two possible control manners. 
     Manner 1: The routing control message includes a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR, and an operation manner. The operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and the neighbor pair, and if the matching succeeds, not to perform an operation of increasing an AS quantity in an AS-path attribute value carried in the second BGP routing message, or if the matching fails, to perform an operation of increasing an AS quantity in an AS-path attribute value. The destination BR is a BR in the second AS. 
     Correspondingly, the processing, by the specified BR according to the routing control message, the BGP routing message advertised to the second AS includes performing matching, by the specified BR, between the identifier of the specified BR and the identifier of the destination BR and the neighbor pair when the specified BR advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, not performing the operation of increasing the AS quantity in the AS-path attribute value carried in the BGP routing message, or if the matching fails, performing the operation of increasing the AS quantity in the AS-path attribute value. 
     Optionally, the routing control message is an extended BGP update update message, and the extended BGP update message includes a BGP policy attribute. The BGP policy attribute is the same as that in  FIG.  4   a    and the embodiment shown in  FIG.  2   , and details are not described herein again. 
     Manner 2: The routing control message includes at least one neighbor pair and an operation manner. The at least one neighbor pair does not include a neighbor pair constituted by an identifier of the first BR and an identifier of the second BR. The operation manner instructs the specified BR to perform matching, when advertising the second BGP routing message to a destination BR in the second AS, between an identifier of the specified BR and an identifier of the destination BR and each of the at least one neighbor pair, and if the matching succeeds, to perform an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not to perform an operation of increasing an AS quantity in an AS-path attribute value. The destination BR is a BR in the second AS. 
     Correspondingly, the processing, by the specified BR according to the routing control message, the BGP routing message advertised to the second AS includes performing matching, by the specified BR, between the identifier of the specified BR and the identifier of the destination BR and each of the at least one neighbor pair when the specified BR advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, performing the operation of increasing the AS quantity in the AS-path attribute value, or if the matching fails, not performing the operation of increasing the AS quantity in the AS-path attribute value. 
     Optionally, the routing control message is an extended BGP update update message, and the extended BGP update message includes a BGP policy attribute. The BGP policy attribute is the same as that in  FIG.  4   b    and the embodiment shown in  FIG.  2   , and details are not described herein again. 
     It should be noted that the “processing” in the processing the BGP routing message advertised to the second AS in this embodiment may include performing a matching-related operation and performing an operation of sending the BGP routing message to the destination BR. 
     It should be noted that the when the specified BR advertises the BGP routing message to the destination BR in the second AS may be understood as before the specified BR advertises the BGP routing message to the destination BR in the second AS. 
     It can be learned from the foregoing embodiment that, according to the solution in this embodiment, the specified border router BR in the first AS receives the routing control message from the controller, and processes, according to the routing control message, the second BGP routing message advertised to the second AS. Therefore, compared with a prior-art method in which configuration is manually performed one by one, this method facilitates automatic and flexible adjustment and control of data traffic flowing into the first AS, simplifies configuration, and saves human power. 
     Corresponding to the method shown in  FIG.  2   ,  FIG.  6    is a schematic structural diagram of a controller  600  according to an embodiment of the application. The controller  600  includes a communications unit  602 , configured to receive a first Border Gateway Protocol BGP routing message, and a processing unit  604 , configured to determine, according to a node that sends the first BGP routing message to the controller, whether to perform incoming-traffic adjustment and control. 
     If determining to perform incoming-traffic adjustment and control, the processing unit  604  is further configured to determine a destination node according to the first BGP routing message, and allocate a source node from a second AS, where the destination node belongs to a first AS, and the second AS is at least one AS that is directly connected to the first AS. 
     The processing unit  604  further obtains a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS. 
     The processing unit  604  is further configured to determine a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS. 
     The communications unit  602  is further configured to send a routing control message to a specified BR, where the specified BR belongs to the first AS, and the routing control message is used to instruct the specified BR to use, when advertising a second BGP routing message to the second AS, the first BR as a next hop for packet forwarding of the second BR. 
     Optionally, a possible manner in which the processing unit  604  determines whether to perform incoming-traffic adjustment and control is as follows. 
     Manner 1: The processing unit  604  performs incoming-traffic adjustment and control if the processing unit  604  determines that the node that sends the first BGP routing message to the controller is a border network device of the first AS, where the border network device of the first AS is a BR device or a provider edge PE device. 
     Manner 2: The processing unit  604  searches a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     Manner 3: The processing unit  604  obtains a first destination prefix according to the first BGP routing message. 
     The processing unit  604  searches a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing incoming-traffic adjustment and control. 
     Further, optionally, a possible manner in which the processing unit  604  determines the destination node according to the first BGP routing message is as follows. 
     Manner 1: The processing unit  604  determines whether at least two first BGP routing messages are received. 
     If determining that at least two first BGP routing messages are received, the processing unit  604  sets a virtual node in the first AS, and determines the virtual node as the destination node. 
     Correspondingly, the intra-domain topology further includes a link between the node that sends the first BGP routing message to the controller and the destination node. 
     Manner 2: The processing unit  604  sets a virtual node in the first AS, and determines the virtual node as the destination node. 
     Correspondingly, the intra-domain topology further includes a link between the border network device of the first AS and the destination node. 
     The obtaining, by the processing unit  604 , a preferred path between the source node and the destination node by using a network topology includes obtaining, by the processing unit  604 , a first affinity attribute constraint condition according to a link between the node that sends the first BGP routing message to the controller and the destination node, and obtaining, by the controller, the preferred path by using the network topology and the first affinity attribute constraint condition. 
     Manner 3: The processing unit  604  may alternatively determine the node that sends the first BGP routing message to the controller, as the destination node. 
     Further, optionally, a possible manner of allocating the source node from the second AS is as follows. 
     Manner 1: The processing unit  604  selects one node from a border router or a virtual node in the second AS, as the source node. 
     Manner 2: The processing unit  604  searches a third configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node. 
     Manner 3: The processing unit  604  obtains a first destination prefix according to the first BGP routing message. 
     The processing unit  604  searches a fourth configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     Further, optionally, the inter-domain topology between the BRs of the first AS and the second AS has two possible cases. 
     Case 1: When the source node is a BR that is in the second AS and that is directly connected to the first AS, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     Case 2: When the source node is a virtual node that is set in the second AS, the topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the source node and the BR of the second AS. 
     Further, optionally, a manner in which the processing unit  604  obtains the inter-domain topology is obtaining, by the processor, a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message, determining, by the processor, whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table, and if determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, establishing, by the processor according to the link identifier, the inter-domain topology between the first AS and an AS that is directly connected to the first AS. 
     It should be noted that descriptions of related content such as the routing control message in this embodiment are the same as those in the method embodiment shown in  FIG.  2   , and details are not described herein again. 
     Corresponding to the method shown in  FIG.  2   ,  FIG.  7    is a schematic structural diagram of a controller  700  according to an embodiment of the application. 
     The controller  700  may be a micro processing computer. For example, the controller  700  may be one of a general-purpose computer, a customized machine, a mobile phone terminal, a tablet, or other portable devices. The controller  700  includes a processor  704 , a memory  706 , a communications interface  702 , and a bus  708 . The processor  704 , the memory  706 , and the communications interface  702  are connected and communicate with each other by using the bus  708 . 
     The bus  708  may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended Industry Standard Architecture (EISA) bus, or the like. The bus may be classified into one or more of an address bus, a data bus, a control bus, or the like. For convenience of denotation, the bus  708  is represented by using only one bold line in  FIG.  7   . However, this does not indicate that there is only one bus or only one type of bus. 
     The memory  706  is a non-transitory computer readable medium configured to store executable program code, where the program code includes a computer operation instruction. When the controller  700  executes the program code, the controller  700  may complete steps  201  to  206  in the embodiment in  FIG.  2   , or may implement all functions of the controller  600  in the embodiment in  FIG.  6   . The memory  706  may include a high speed RAM (Random Access Memory) memory. Optionally, the memory  706  may further include a non-volatile memory (non-volatile memory). For example, the memory  706  may include a magnetic disk storage. 
     The processor  704  may be a central processing unit (CPU), or the processor  704  may be an application-specific integrated circuit (ASIC), or the processor  704  may be configured as one or more integrated circuits implementing an embodiment of the application. 
     The processor  704  is configured to perform all operations performed by the processing unit  604  of the controller  600  shown in  FIG.  6   , and details are not described herein again. 
     The communications interface  702  is configured to perform all operations performed by the communications unit  602  of the controller  600  shown in  FIG.  6   , and details are not described herein again. 
     Corresponding to the method shown in  FIG.  5   ,  FIG.  8    is a schematic structural diagram of a border router  800  according to an embodiment of the application. The border router  800  is used as a specified border router BR, and the specified border router  800  includes a communications unit  802 , configured to receive a routing control message from a controller, where the routing control message is used to instruct the specified BR to use, when advertising a BGP routing message to a second AS, a first BR as a next hop for packet forwarding of a second BR, the first BR belongs to a first AS, the second BR belongs to the second AS, and the controller is configured to manage the first AS, and a processing unit  804 , configured to process, according to the routing control message, the BGP routing message advertised to the second AS. 
     Optionally, the routing control message may have multiple specific forms, and the routing control message has multiple possible control manners. This is the same as the embodiment shown in  FIG.  5   . For details, refer to a related part in  FIG.  5   . Details are not described herein again. Corresponding to the embodiment shown in  FIG.  5   , the following describes specific operations performed by the processing unit  804  in two possible control manners of the routing control message. 
     When the control manner in Manner 1 in the embodiment shown in  FIG.  5    is used, the processing, by the processing unit  804  according to the routing control message, the BGP routing message advertised to the second AS specifically includes matching, by the processing unit  804 , an identifier of the specified BR and an identifier of a destination BR with a neighbor pair when the communications unit  802  advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, not performing an operation of increasing an AS quantity in an AS-path attribute value carried in the BGP routing message, or if the matching fails, performing an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS. 
     Further, optionally, the communications unit  802  is further configured to send the BGP routing message to the destination BR. 
     When the control manner in Manner 2 in the embodiment shown in  FIG.  5    is used, the processing, by the processing unit  804  according to the routing control message, the BGP routing message advertised to the second AS specifically includes matching, by the processing unit  804 , an identifier of the specified BR and an identifier of a destination BR with each of at least one neighbor pair when the communications unit  802  advertises the BGP routing message to the destination BR in the second AS, and if the matching succeeds, performing an operation of increasing an AS quantity in an AS-path attribute value, or if the matching fails, not performing an operation of increasing an AS quantity in an AS-path attribute value, where the destination BR is a BR in the second AS. 
     Further, optionally, the communications unit  802  is further configured to send the BGP routing message to the destination BR. 
     Corresponding to the method shown in  FIG.  5   ,  FIG.  9    is a schematic structural diagram of a border router  900  according to an embodiment of the application. 
     The border router  900  may be a micro processing computer. For example, the border router  900  may be one of a general-purpose computer, a customized machine, a mobile phone terminal, a tablet, or other portable devices. The border router  900  includes a processor  904 , a memory  906 , a communications interface  902 , and a bus  908 . The processor  904 , the memory  906 , and the communications interface  902  are connected and communicate with each other by using the bus  908 . 
     The bus  908  may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended Industry Standard Architecture (EISA) bus, or the like. The bus may be classified into one or more of an address bus, a data bus, a control bus, or the like. For convenience of denotation, the bus  908  is represented by using only one bold line in  FIG.  9   . However, this does not indicate that there is only one bus or only one type of bus. 
     The memory  906  is configured to store executable program code, where the program code includes a computer operation instruction. When the border router  900  executes the program code, the border router  900  may complete step  501  and step  502  in the embodiment in  FIG.  5   , or may implement all functions of the border router  800  in the embodiment in  FIG.  8   . The memory  906  may include a high speed RAM (Random Access Memory) memory. Optionally, the memory  906  may further include a non-volatile memory (non-volatile memory). For example, the memory  906  may include a magnetic disk storage. 
     The processor  904  may be a central processing unit (CPU), or the processor  904  may be an application-specific integrated circuit (ASIC), or the processor  904  may be configured as one or more integrated circuits implementing an embodiment of the application. 
     The processor  904  is configured to perform all operations performed by the processing unit  804  of the controller  800  shown in  FIG.  8   , and details are not described herein again. 
     The communications interface  902  is configured to perform all operations performed by the communications unit  802  of the controller  800  shown in  FIG.  8   , and details are not described herein again. 
       FIG.  18    shows a network system  1800  provided in an embodiment of the application. The network system  1800  includes the controller  600  provided in the embodiment shown in  FIG.  6    and the border router  800  provided in the embodiment shown in  FIG.  8   . 
     Alternatively, the network system  1800  includes the controller  700  provided in the embodiment shown in  FIG.  7    and the border router  900  provided in the embodiment shown in  FIG.  9   . 
     2. Outgoing-Traffic Routing Control Method, Apparatus, and System 
     The outgoing-traffic routing control method in the embodiments of the application includes processing on a controller side and a border router side. The following provides descriptions separately. 
       FIG.  10    is a simplified flowchart of a routing control method on a controller side according to an embodiment of the application. If the method is applied to a network scenario similar to that shown in  FIG.  1   , the method includes the operations described below. It should be noted that the method shown in  FIG.  10    not only can be applied to a network structure shown in  FIG.  1    but also can be applied to another type of network system, for example, a network system constituted by a network device that does not use any replaceable component. 
       1001 : A controller receives a Border Gateway Protocol BGP routing message, where the controller is configured to manage a first autonomous system AS. 
       1002 : The controller determines, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control. 
     Optionally, there are the following several possible manners in which the controller determines to perform outgoing-traffic adjustment and control. 
     Manner 1: The controller performs outgoing-traffic adjustment and control if the controller determines that the node that sends the BGP routing message to the controller is a BR of the first AS. 
     With reference to the example in  FIG.  1   , the node that sends the first BGP routing message to the controller may be the border router BR 100 - 1 , the border router BR 100 - 2 , or the border router BR 100 - 3 . All these devices are border routers of the AS 1 . When receiving the first BGP routing message sent from these border routers of the AS 1 , the controller  130  determines to perform outgoing-traffic adjustment and control. This is a manner of random adjustment and control performed according to a node role. 
     Manner 2: The controller searches a first configuration information table by using the node that sends the BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller is the border router BR 100 - 1 , the controller  130  searches, by using an identifier of the border router BR 100 - 1  as a match item, a configuration information table shown in Table 5, to obtain an operation manner that is outgoing-traffic adjustment and control. This is a type of coarse-grained traffic adjustment and control for a node. 
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
               
            
               
                   
                 Match item 
                 Operation manner 
               
               
                   
                   
               
               
                   
                 Identifier of the 
                 Outgoing-traffic 
               
               
                   
                 border router BR100-1 
                 adjustment and control 
               
               
                   
                 Identifier of the 
                 Outgoing-traffic 
               
               
                   
                 border router BR100-2 
                 adjustment and control 
               
               
                   
                 Identifier of the 
                 Outgoing-traffic 
               
               
                   
                 border router BR100-3 
                 adjustment and control 
               
               
                   
                   
               
            
           
         
       
     
     Manner 3: The controller obtains a first destination prefix according to the BGP routing message. 
     The controller searches a second configuration information table by using the node that sends the BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller  130  is the border router BR 100 - 1 , and a destination prefix obtained by the controller  130  from the first BGP routing message is the prefix 2 (for example, an IP address prefix 20.1.0.0/16 or an IP address 20.1.1.1/32, the prefix 2 is a prefix of a routing destination in a network, and is further used to identify the virtual node  210 - 1  in this embodiment of the application), the controller  130  searches, by using an identifier (which may be, for example, an IP address) of the border router BR 100 - 1  and the prefix 2 as a match item, a configuration information table shown in Table 6, to obtain an operation manner that is outgoing-traffic adjustment and control. This is a fine-grained traffic adjustment and control manner for a node and a prefix. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
            
               
                 Match item 
                   
               
            
           
           
               
               
               
            
               
                 Device identifier 
                 Destination prefix 
                 Operation manner 
               
               
                   
               
               
                 Identifier of the 
                 Prefix 2 
                 Incoming-traffic 
               
               
                 border router BR100-1 
                   
                 adjustment and control 
               
               
                 Identifier of the 
                 Prefix 2 
                 Incoming-traffic 
               
               
                 border router BR100-2 
                   
                 adjustment and control 
               
               
                 Identifier of the 
                 Prefix 3 
                 Incoming-traffic 
               
               
                 border router BR100-3 
                   
                 adjustment and control 
               
               
                   
               
            
           
         
       
     
       1003 : If determining to perform outgoing-traffic adjustment and control, the controller determines a destination node according to the BGP routing message, and allocates a source node from the first AS, where the destination node belongs to a second AS, and the second AS is at least one AS that is directly connected to the first AS. 
     Optionally, a manner of allocating the source node from the first AS may be as follows. 
     Manner 1: The controller determines the node that sends the BGP routing message to the controller, as the source node, or the controller determines a border network device of the first AS as the source node, where the border network device is a BR device or a provider edge PE device. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller  130  is the border router BR 100 - 1 , the BR 100 - 1  is determined as the source node, or with reference to the example in  FIG.  1   , the border network device of the first AS includes the border router BR 100 - 1 , the border router BR 100 - 2 , the border router BR 100 - 3 , the PE device  110 - 1 , and the PE device  110 - 2 , and the source node is selected from these border network devices. 
     It should be noted that the source node may alternatively be selected from a P device in a domain of the first AS. This is not limited herein. 
     Manner 2: The controller searches a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller is the border router BR 100 - 1 , the controller  130  searches, by using the identifier of the border router BR 100 - 1  as a match item, a configuration information table shown in Table 7, to obtain a source node that is the border router BR 100 - 1 . 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
               
            
               
                   
                 Match item 
                 Source node 
               
               
                   
                   
               
               
                   
                 Identifier of the 
                 Identifier of the 
               
               
                   
                 border router BR100-1 
                 border router BR100-1 
               
               
                   
                 Identifier of the 
                 Identifier of the 
               
               
                   
                 border router BR100-2 
                 border router BR100-1 
               
               
                   
                 Identifier of the 
                 Identifier of the 
               
               
                   
                 border router BR100-3 
                 border router BR100-2 
               
               
                   
                   
               
            
           
         
       
     
     Manner 3: The controller obtains a first destination prefix according to the first BGP routing message. 
     The controller searches a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     With reference to the example in  FIG.  1   , for example, if the node that sends the first BGP routing message to the controller  130  is the border router BR 100 - 1 , and a destination prefix obtained by the controller  130  from the first BGP routing message is the prefix 2 (for example, the IP address prefix 20.1.0.0/16 or the IP address 20.1.1.1/32, the prefix 2 is a prefix of a routing destination in a network, and is further used to identify the virtual node  210 - 1  in this embodiment of the application), the controller  130  searches, by using the identifier (which may be, for example, the IP address) of the border router BR 100 - 1  and the prefix 2 as a match item, a configuration information table shown in Table 8, to obtain a source node that is the border router BR 100 - 1 . 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Configuration information table 
               
            
           
           
               
               
            
               
                 Match item 
                   
               
            
           
           
               
               
               
            
               
                 Device identifier 
                 Destination prefix 
                 Source node 
               
               
                   
               
               
                 Identifier of the 
                 Prefix 2 
                 Identifier of the 
               
               
                 border router BR100-1 
                   
                 border router BR100-1 
               
               
                 Identifier of the 
                 Prefix 2 
                 Identifier of the 
               
               
                 border router BR100-2 
                   
                 border router BR100-1 
               
               
                 Identifier of the 
                 Prefix 3 
                 Identifier of the 
               
               
                 border router BR100-3 
                   
                 border router BR100-3 
               
               
                   
               
            
           
         
       
     
       1004 : The controller obtains a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS. 
     Optionally, the intra-domain topology of the first AS may include multiple cases. This is the same as related descriptions in the embodiment shown in  FIG.  2   , and details are not described herein again. 
     Optionally, a manner of determining the destination node and determining the inter-domain topology between the BRs of the first AS and the second AS may be as follows. 
     Manner 1: If a BR in the second AS is determined as the destination node, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     With reference to the example in  FIG.  1   , the inter-domain topology includes the BR 200 - 1 , the BR 200 - 2 , the BR 100 - 1 , the BR 100 - 2 , and a link that connects these nodes. 
     Manner 2: If the destination node is a virtual node that is set in the second AS, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the destination node and the BR of the second AS. 
     With reference to the example in  FIG.  1   , the inter-domain topology includes the BR 200 - 1 , the BR 200 - 2 , the BR 100 - 1 , the BR 100 - 2 , and a link that connects these nodes. The inter-domain topology further includes the virtual node  210 - 1 , a virtual link between the virtual node  210 - 1  and the BR 200 - 1 , and a virtual link between the virtual node  210 - 1  and the BR 200 - 2 . 
     Optionally, a manner in which the controller obtains the inter-domain topology may be as follows. 
     Manner 1: The controller establishes a link between a BR that is identified by a next-hop field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the next-hop field belongs to the second AS, or the controller establishes a link between a BR that is identified by a community attribute field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the community attribute field belongs to the second AS. 
     Manner 2: The controller obtains a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message. The controller determines whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table. If determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, the controller establishes the inter-domain topology between the first AS and the second AS according to the link identifier. 
     Correspondingly, the obtaining, by the controller, a preferred path between the source node and the destination node by using a network topology includes obtaining, by the controller, an affinity attribute constraint condition according to a link between the node that sends the BGP routing message to the controller and the BR of the second AS, and obtaining, by the controller, the preferred path by using the network topology and the affinity attribute constraint condition. 
     With reference to the example in  FIG.  1   , the preferred path is a path of outgoing data traffic from the BR 100 - 1 , through the BR 200 - 1 , to the virtual node  210 - 1 . 
     It should be noted that, as shown in  FIG.  11   a   , the source node may alternatively be the BR 100 - 3  in the AS 1 , and the preferred path is a path of outgoing data traffic from the BR 100 - 3 , through the BR 100 - 1  and the BR 200 - 1 , to the virtual node  210 - 1 . 
     As shown in  FIG.  11   b   , the source node may alternatively be the PE device  110 - 1  in the AS 1 , and the preferred path is a path of outgoing data traffic from the PE device  110 - 1 , through the BR 100 - 1  and the BR 200 - 1 , to the virtual node  210 - 1 . 
     It should be noted that there may also be a P device in an AS 1  domain. In a possible scenario, the P device in the AS 1  domain may also be included on the preferred path. 
       1005 : The controller determines a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS. 
     With reference to the example in  FIG.  1   , the first BR is the BR 100 - 1 , and the second BR is the BR 200 - 1 . 
       1006 : The controller sends a routing control message to the first BR, where the routing control message is used to instruct the first BR to use the second BR as a next hop for packet forwarding. 
     Optionally, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from the BGP routing message. 
     The routing control message may have multiple specific forms, and may be an extended BGP update update message. Specifically, the routing control message may alternatively be a BGP FLOWSPEC message, or may be an extended OpenFlow OpenFlow protocol of software-defined networking SDN. 
     The following uses the extended BGP update message as an example for description. The function may be implemented by adding a new BGP policy attribute. As shown in  FIG.  12   , the newly added BGP policy attribute includes a match field and an action field. 
     The match field includes a match type field, a sub-type length value sub-TLV quantity field, and a sub-TLV field. A possible value of the match type field is 0 (indicating permission) or 1 (indicating rejection). With reference to the example of outgoing-traffic adjustment and control in  FIG.  1   , a value of the match type field is 0, indicating permission. 
     The sub-type length value sub-TLV quantity field indicates a quantity of sub-TLVs carried in the match field, and a value of the sub-type length value sub-TLV quantity field may be a positive integer greater than or equal to 0. With reference to the example of outgoing-traffic adjustment and control in  FIG.  1   , the value of the sub-TLV quantity field is 1. 
     The sub-TLV field includes a sub-type sub-type field, a sub-length sub-length field, and a sub-value sub-value field. A possible value of the sub-type sub-type field is as follows. Sub-type=1, instructing to match an IPv4 neighbor pair, that is, a neighbor pair in which each device identifier is identified by using an IPv4 address, or sub-type=2, instructing to match an IPv6 neighbor pair, that is, a neighbor pair in which each device identifier is identified by using an IPv6 address. 
     The sub-length field indicates a length of the sub-TLV or a length of the sub-value field. The sub-value field includes a neighbor pair constituted by a neighbor local device identifier field and a neighbor peer device identifier field. With reference to the example of outgoing-traffic adjustment and control in  FIG.  1   , the neighbor local device identifier field carries an identifier (BR 100 - 1 ) of the first BR, and the neighbor peer device identifier field carries an identifier (BR 200 - 2 ) of the second BR. 
     The action field includes an action type field, an action length field, and an action value field. A possible value of the action type (Action Type) field includes but is not limited to the following. Action type=1, instructing to perform a preferred-routing operation, or action type=2, instructing to perform an operation of increasing an AS-path (AS-Path) length. 
     With reference to the example of outgoing-traffic adjustment and control in  FIG.  1   , action type=1, instructing to perform the preferred-routing operation. 
     The action length field indicates a length of the action field or a length of the action value field. In this case, the action value field has no meaning, and specifically, may be empty, or carry an invalid value, or not exist. 
     The BGP policy attribute instructs the first BR to perform matching between the identifier of the first BR and the neighbor local device identifier field in the neighbor pair field, and if the matching succeeds, to perform an operation of using the second BR as the next hop for routing to the destination prefix. 
     It should be noted that multiple formats may be used for the routing control message. The format shown in  FIG.  12    is merely a specific example. However, an application and a message format that are described herein are not limited to disclosed specific forms. Instead, this disclosure covers all modifications, equivalents, and replacements falling within the scope of the accompanying claims. 
     It can be learned from the foregoing embodiment that, according to the solution in this embodiment, the controller receives the first BGP routing message, then automatically determines to perform outgoing-traffic control, calculates the preferred path from the source node to the destination node, obtains the first BR and the second BR on the preferred path, sends the routing control message to the first BR in the first AS controlled by the controller, and instructs the first BR to use the second BR as the next hop for packet forwarding. Therefore, compared with a prior-art method in which configuration is manually performed one by one, this method facilitates automatic and flexible adjustment and control of data traffic flowing out of the first AS, simplifies configuration, and saves human power. 
       FIG.  13    is a simplified flowchart of a routing control method on a border router side according to an embodiment of the application. If the method is applied to a network scenario similar to that shown in  FIG.  1   , the method includes the operations described below. It should be noted that the method shown in  FIG.  13    not only can be applied to a network structure shown in  FIG.  1   , but also can be applied to another type of network system, for example, a network system constituted by a network device that does not use any replaceable component. 
       1301 : A first border router BR in a first AS receives a routing control message from a controller, where the routing control message is used to instruct the first BR to use a second BR as a next hop for packet forwarding, and the second BR belongs to a second AS. 
       1302 : The first BR determines, according to the routing control message, the second BR as the next hop for packet forwarding. 
     It should be noted that the embodiment shown in  FIG.  13    is corresponding to the routing control method on the controller side. Descriptions of the routing control message are the same as those in the embodiment shown in  FIG.  10   , and details are not described herein again. 
     It can be learned from the foregoing embodiment that, according to the solution in this embodiment, the first BR in the first AS receives the routing control message from the controller, and determines, according to the routing control message, the second BR as the next hop for packet forwarding of the first BR. Therefore, compared with a prior-art method in which BR configuration is manually performed one by one, this method facilitates automatic and flexible adjustment and control of data traffic flowing out of the first AS, simplifies configuration, and saves human power. 
     Corresponding to the method shown in  FIG.  10   ,  FIG.  14    is a schematic structural diagram of a controller  1400  according to an embodiment of the application. The controller  1400  is configured to manage a first autonomous system AS, and the controller  1400  includes a communications unit  1402 , configured to receive a Border Gateway Protocol BGP routing message, and a processing unit  1404 , configured to determine, according to a node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control. 
     If determining to perform outgoing-traffic adjustment and control, the processing unit  1404  is further configured to determine a destination node according to the BGP routing message, and allocate a source node from the first AS, where the destination node belongs to a second AS, and the second AS is at least one AS that is directly connected to the first AS. 
     The processing unit  1404  is further configured to obtain a preferred path between the source node and the destination node by using a network topology, where the network topology includes an intra-domain topology of the first AS and an inter-domain topology between BRs of the first AS and the second AS. 
     The processing unit  1404  is further configured to determine a first BR and a second BR on the preferred path according to the preferred path, where the first BR belongs to the first AS, and the second BR belongs to the second AS. 
     The processing unit  1404  is further configured to send a routing control message to the first BR, where the routing control message is used to instruct the first BR to use the second BR as a next hop for packet forwarding. 
     Optionally, there may be the following manners of determining, according to the node that sends the BGP routing message to the controller, whether to perform outgoing-traffic adjustment and control. 
     Manner 1: The processing unit  1404  is further configured to perform outgoing-traffic adjustment and control if determining that the node that sends the BGP routing message to the controller is a BR of the first AS. 
     Manner 2: The processing unit  1404  is further configured to search a first configuration information table by using the node that sends the BGP routing message to the controller, as a first match item, to obtain an operation corresponding to the first match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     Manner 3: The processing unit  1404  is further configured to obtain a first destination prefix according to the BGP routing message. 
     The processing unit  1404  is further configured to search a second configuration information table by using the node that sends the BGP routing message to the controller and the first destination prefix as a second match item, to obtain an operation corresponding to the second match item, where the obtained operation is performing outgoing-traffic adjustment and control. 
     Further, optionally, a manner of allocating the source node from the first AS may be as follows the processing unit  1404  is further configured to search a first configuration information table by using the node that sends the first BGP routing message to the controller, as a first match item, to obtain a source node corresponding to the first match item, as the source node, or obtaining, by the processing unit  1404 , a first destination prefix according to the first BGP routing message, and searching, by the processing unit  1404 , a second configuration information table by using the node that sends the first BGP routing message to the controller and the first destination prefix as a second match item, to obtain a source node corresponding to the second match item, as the source node. 
     Further, optionally, a manner of determining the destination node and determining the inter-domain topology between the BRs of the first AS and the second AS may be as follows. 
     If the destination node is a BR in the second AS, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS. 
     If the destination node is a virtual node that is set in the second AS, the inter-domain topology between the BRs of the first AS and the second AS includes an inter-domain topology between a BR of the first AS and a BR of the second AS, and a topology between the destination node and the BR of the second AS. 
     Further, optionally, a manner in which the controller obtains the inter-domain topology is the following. 
     Manner 1: The processing unit  1404  is further configured to establish a link between a BR that is identified by a next-hop field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the next-hop field belongs to the second AS, or the processing unit  1404  is further configured to establish a link between a BR that is identified by a community attribute field included in the BGP routing message and the node that sends the BGP routing message to the controller, to obtain the inter-domain topology, where the BR identified by the community attribute field belongs to the second AS. 
     Manner 2: The processing unit  1404  is further configured to obtain a direct route of the BR of the first AS by using an Interior Gateway Protocol IGP routing message. 
     The processing unit  1404  is further configured to determine whether the obtained direct route and a link identifier are stored in a match item of a link information configuration table. 
     If determining that the obtained direct route and the link identifier are stored in the match item of the link information configuration table, the processing unit  1404  is further configured to establish the inter-domain topology between the first AS and the second AS according to the link identifier. 
     Correspondingly, that the processing unit  1404  is further configured to obtain a preferred path between the source node and the destination node by using a network topology includes obtaining, by the processing unit, an affinity attribute constraint condition according to a link between the node that sends the BGP routing message to the controller and the BR of the second AS, and obtaining, by the processing unit, the preferred path by using the network topology and the affinity attribute constraint condition. 
     Further, optionally, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from the BGP routing message. 
     It should be noted that descriptions of the routing control message in this embodiment are the same as those in the method embodiment shown in  FIG.  10   , and details are not described herein again. 
     Corresponding to the method shown in  FIG.  10   ,  FIG.  15    is a schematic structural diagram of a controller  1500  according to an embodiment of the application. 
     The controller  1500  may be a micro processing computer. For example, the controller  1500  may be one of a general-purpose computer, a customized machine, a mobile phone terminal, a tablet, or other portable devices. The controller  1500  includes a processor  1504 , a memory  1506 , a communications interface  1502 , and a bus  1508 . The processor  1504 , the memory  1506 , and the communications interface  1502  are connected and communicate with each other by using the bus  1508 . 
     The bus  1508  may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended Industry Standard Architecture (EISA) bus, or the like. The bus may be classified into one or more of an address bus, a data bus, a control bus, or the like. For convenience of denotation, the bus  1508  is represented by using only one bold line in  FIG.  15   . However, this does not indicate that there is only one bus or only one type of bus. 
     The memory  1506  is configured to store executable program code, where the program code includes a computer operation instruction. When the controller  1500  executes the program code, the controller  1500  may complete steps  1001  to  1006  in the embodiment in  FIG.  10   , or may implement all functions of the controller  1400  in the embodiment in  FIG.  14   . The memory  1506  may include a high speed RAM (Random Access Memory) memory. Optionally, the memory  1506  may further include a non-volatile memory (non-volatile memory). For example, the memory  1506  may include a magnetic disk storage. 
     The processor  1504  may be a central processing unit (CPU), or the processor  1504  may be an application-specific integrated circuit (ASIC), or the processor  1504  may be configured as one or more integrated circuits implementing an embodiment of the application. 
     The processor  1504  is configured to perform all operations performed by the processing unit  1404  of the controller  1400  shown in  FIG.  14   , and details are not described herein again. 
     The communications interface  1502  is configured to perform all operations performed by the communications unit  1402  of the controller  1400  shown in  FIG.  14   , and details are not described herein again. 
     Corresponding to the method shown in  FIG.  13   ,  FIG.  16    is a schematic structural diagram of a network device  1600  according to an embodiment of the application. The network device  1600  is used as a first border router BR, and the first border router  1600  includes a communications unit  1602 , configured to receive a routing control message from a controller, where the routing control message is used to instruct the first BR to use a second BR as a next hop for packet forwarding, and the second BR belongs to a second AS, and a processing unit  1604 , configured to determine, according to the routing control message, the second BR as the next hop for packet forwarding. 
     Optionally, the routing control message includes a destination prefix, an identifier of the second BR, and an operation manner, the operation manner instructs the first BR to use the second BR as a next hop for routing to the destination prefix, and the destination prefix is obtained from a BGP routing message. 
     Correspondingly, the processing unit  1604  sets the next hop for routing to the destination prefix to the second BR. 
     It should be noted that the routing control message may have multiple specific forms. Descriptions of the routing control message are the same as those in the embodiments shown in  FIG.  13    and  FIG.  10   . For details, refer to related parts in  FIG.  13    and  FIG.  10   . Details are not described herein again. 
     Corresponding to the method shown in  FIG.  13   ,  FIG.  17    is a schematic structural diagram of a border router  1700  according to an embodiment of the application. 
     The border router  1700  may be a micro processing computer. For example, the border router  1700  may be one of a general-purpose computer, a customized machine, a mobile phone terminal, a tablet, or other portable devices. The border router  1700  includes a processor  1704 , a memory  1706 , a communications interface  1702 , and a bus  1708 . The processor  1704 , the memory  1706 , and the communications interface  1702  are connected and communicate with each other by using the bus  1708 . 
     The bus  1708  may be an Industry Standard Architecture (ISA) bus, a Peripheral Component Interconnect (PCI) bus, an Extended Industry Standard Architecture (EISA) bus, or the like. The bus may be classified into one or more of an address bus, a data bus, a control bus, or the like. For convenience of denotation, the bus  1708  is represented by using only one bold line in  FIG.  17   . However, this does not indicate that there is only one bus or only one type of bus. 
     The memory  1706  is configured to store executable program code, where the program code includes a computer operation instruction. When the border router  1700  executes the program code, the border router  1700  may complete step  1301  and step  1302  in the embodiment in  FIG.  13   , or may implement all functions of the border router  1600  in the embodiment in  FIG.  16   . The memory  1706  may include a high speed RAM (Random Access Memory) memory. Optionally, the memory  1706  may further include a non-volatile memory (non-volatile memory). For example, the memory  1706  may include a magnetic disk storage. 
     The processor  1704  may be a central processing unit (CPU), or the processor  1704  may be an application-specific integrated circuit (ASIC), or the processor  1704  may be configured as one or more integrated circuits implementing an embodiment of the application. 
     The processor  1704  is configured to perform all operations performed by the processing unit  1604  of the controller  1600  shown in  FIG.  16   , and details are not described herein again. 
       FIG.  19    shows a network system  1900  provided in an embodiment of the application. The network system  1900  includes the controller  1400  provided in the embodiment shown in  FIG.  14    and the border router  1600  provided in the embodiment shown in  FIG.  16   . 
     Alternatively, the network system  1800  includes the controller  1500  provided in the embodiment shown in  FIG.  15    and the border router  1700  provided in the embodiment shown in  FIG.  17   . 
     Finally, it should be noted that the foregoing embodiments are used merely as examples for describing the technical solutions of the application, but are not intended to limit the application. Each feature disclosed in the specification and, in a proper situation, in the claims and the accompanying drawings may be provided independently or be provided in any proper combination. A feature described as being implemented by hardware may alternatively be implemented by software, and vice versa. Although the application is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some or all technical features thereof, without departing from the scope of the technical solutions in the embodiments of the application.