Abstract:
Embodiments of the present invention disclose apparatuses. The apparatus includes a program instructing hardware and a computer readable storage medium coupled to the hardware and storing programming instructions for execution by the hardware, the programming instructions instruct the hardware to: receive a network device selection message sent by a first network device, where the network device selection message contains a virtual local area network (VLAN) mapping capability identifier of the first network device and a device identifier of the first network device; when determining that both the apparatus and the first network device have VLAN mapping capability according to local VLAN mapping capability and the VLAN mapping capability identifier of the first network device, select a network device for executing VLAN mapping according to sizes or a sequence of a local device identifier and the device identifier of the first network device.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/937,938, filed on Jul. 9, 2013, which is a continuation of International Patent Application No. PCT/CN2011/080809, filed on Oct. 14, 2011, which claims priority to Chinese Patent Application No. 201110004507.0, filed on Jan. 11, 2011. The afore-mentioned patent applications are hereby incorporated by reference in their entireties. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to the field of network communications, and in particular to a method, an apparatus, and a system for selecting a network device. 
       BACKGROUND 
       [0003]    An Ethernet tree (E-Tree) is an Ethernet virtual circuit (EVC) service defined by the metro Ethernet forum (MEF). The E-Tree has the following features: 
         [0004]    A root (Root) node and a leaf (Leaf) node are in a one-to-multiple relationship, and multiple Root nodes may exist; 
         [0005]    a Root node may send an Ethernet frame to any other Root node and any Leaf node, and a Leaf node may send an Ethernet frame to any Root node; and 
         [0006]    a Leaf node cannot directly connect to and must be isolated from another Leaf node. 
         [0007]    A virtual private local area network service (VPLS) is a technology which uses wide area network (WAN) architecture to virtualize an Ethernet local area network. The VPLS is capable of providing a multipoint-to-multipoint connection, similar to that of a local area network (LAN), on a multi-protocol label switching (MPLS) network, which makes it convenient for users to simultaneously access the MPLS network from multiple geographically scattered points and access each other, as if these points were directly connected to a LAN. Because currently core networks mainly use an Internet Protocol (IP)/MPLS technology, requirements of providing a virtual Ethernet service through the VPLS is increasing and it has already been widely deployed. 
         [0008]    An existing technology for providing the E-Tree by using the VPLS is to use different virtual local area networks (VLAN) to identify whether Ethernet frames come from a Root node or a Leaf node: On a provider edge (Provider Edge, PE) device, a corresponding root VLAN identifier or leaf VLAN identifier is added according to whether an E-Tree access port is a root or leaf, and then a packet marked with the root VLAN identifier or leaf VLAN identifier is transferred through a pseudo wire (PW) to a peer PE; and on the peer PE, the VLAN identifier carried in the packet is converted into a local VLAN identifier, and then corresponding forwarding or filtering is performed; for example, a frame from a root VLAN is forwarded on a leaf port, a frame from a leaf VLAN is filtered on the leaf port, and the like. 
         [0009]    For higher network scalability, each PE may generally use an independent VLAN space of its own, and a PE with a unidirectional PW egress performs appropriate VLAN translation. For example, there is a bidirectional PW between a PE  1  and a PE  2 , that is, a PW  1  in a forward direction and a PW  2  in a reverse direction are connected; E-Tree service types on the PE  1  are identified as Root 1  VLAN and Leaf 1  VLAN; and E-Tree service types on the PE  2  are identified as Root 2  VLAN and Leaf 2  VLAN. The value of the Root 1  VLAN may be different from the value of the Root 2  VLAN, and the value of the Leaf 1  VLAN may be different from the value of the Leaf 2  VLAN. Therefore, an E-Tree service packet borne on the PW  1  in the forward direction from the PE  1  to the PE  2  carries Root 1  VLAN or Leaf 1  VLAN, which is converted on the egress PE  2  into Root 2  VLAN or Leaf 2  VLAN, respectively; and an E-Tree service packet borne on the PW  2  in the reverse direction from the PE  2  to the PE  1  carries Root 2  VLAN or Leaf 2  VLAN, which is converted on the egress PE  1  into Root 1  VLAN or Leaf 1  VLAN, respectively. In this way, four different VLAN identifiers appear on the bidirectional PW, bringing difficulties in E-Tree service maintenance and detection. 
       SUMMARY 
       [0010]    Embodiments of the present invention provide a method, an apparatus, and a system for selecting a network device so as to solve the following problem during E-Tree service providing in the prior art: When a PE uses an independent VLAN space, four different VLAN identifiers exist on a bidirectional PW, bringing difficulties in E-Tree service maintenance and detection. 
         [0011]    To solve the foregoing technical problem, an embodiment of the present invention provides a method for selecting a network device, including: 
         [0012]    receiving, by a second network device, a network device selection message sent by a first network device, where the network device selection message contains a VLAN mapping capability identifier of the first network device; and 
         [0013]    selecting, by the second network device, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. 
         [0014]    An embodiment of the present invention provides an apparatus for selecting a network device, including: 
         [0015]    a receiving module, configured to receive a network device selection message sent by a first network device, where the network device selection message contains a VLAN mapping capability identifier of the first network device; and 
         [0016]    a selecting module, configured to select, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. 
         [0017]    An embodiment of the present invention provides a system for selecting a network device, including: 
         [0018]    a first network device, configured to send a network device selection message to a second network device, where the network device selection message contains a VLAN mapping capability identifier; and 
         [0019]    a second network device, configured to receive the network device selection message, and select, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. 
         [0020]    By using the technical solutions provided in the embodiments of the present invention, it may be ensured that VLAN mapping is executed for a PW in a forward direction and a PW in a reverse direction on a same PE, and there are only two VLAN identifiers on a bidirectional PW, thereby ensuring consistency of VLANs in the bidirectional PW and making it simpler and easier to maintain and detect the PW. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0021]    To describe the technical solutions in the embodiments of the present invention or in the prior art more clearly, the following briefly introduces accompanying drawings required for describing the embodiments or the prior art. Apparently, the accompanying drawings in the following description show merely some embodiments of the present invention, and a person having ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts. 
           [0022]      FIG. 1  is a flowchart of a method for selecting a network device according to a first embodiment of the present invention; 
           [0023]      FIG. 2  is a schematic diagram of a network on which an E-Tree service is provided by using a VPLS technology; 
           [0024]      FIG. 3  is a flowchart of a method for selecting a network device according to a second embodiment of the present invention; 
           [0025]      FIG. 4  is a block diagram of an apparatus for selecting a network device according to a third embodiment of the present invention; and 
           [0026]      FIG. 5  is a schematic diagram of a system for selecting a network device according to a fourth embodiment of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    The following is an exemplary description of a specific implementation process of the present invention by using embodiments. Apparently, the embodiments described in the following are merely a part rather than all of the embodiments of the present invention. All other embodiments obtained by a person having ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention. 
         [0028]    An embodiment of the present invention provides a method for selecting a network device. The method includes: receiving, by a second network device, a network device selection message sent by a first network device, where the network device selection message contains a VLAN mapping capability identifier of the first network device; and selecting, by the second network device, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. By using the technical solution provided in this embodiment of the present invention, it may be ensured that VLAN mapping is executed for a PW in a forward direction and a PW in a reverse direction on a same PE, and there are only two VLAN identifiers on a bidirectional PW, thereby ensuring consistency of VLANs in the bidirectional PW and making it simpler and easier to maintain and detect the PW. 
         [0029]    To make the objectives, features, and advantages of the embodiment of the present invention more obvious and comprehensible, the following further describes this embodiment of the present invention in detail with reference to the accompanying drawings and specific embodiments. 
         [0030]    Refer to  FIG. 1 , which is a flowchart of a method for selecting a network device according to a first embodiment of the present invention. Specific steps are as follows: 
         [0031]    Step  101 : A second network device receives a network device selection message sent by a first network device, where the network device selection message contains a VLAN mapping capability identifier of the first network device. 
         [0032]    The first network device and the second network device may be provider edge PE devices on a VPLS network. The first network device may carry the VLAN mapping capability identifier of the first network device by extending a label distribution protocol (LDP) message or a border gateway protocol (BGP) message. 
         [0033]    Step  102 : The second network device selects, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. 
         [0034]    The selecting a network device for executing VLAN mapping is completed through automatic negotiation according to the VLAN mapping capability identifier. For example, as shown in  FIG. 2 , a bidirectional PW needs to be established between a PE  1  and a PE  2  so as to provide an E-Tree service. The bidirectional PW is formed of a PW  1  in a forward direction and a PW  2  in a reverse direction. During establishment of the PW  1  in the forward direction, the PE  2  at an egress end sends an extended LDP message to the PE  1  at an ingress end, where an E-Tree-related sub-TLV (sub TLV) is added in a PW interface parameter TLV (Type-Length-Value) in the extended LDP message, to carry a VLAN mapping capability identifier V 2  of the PE  2 . After receiving the extended LDP message, the PE  1  establishes the PW  1  in the forward direction and selects, according to local VLAN mapping capability and the V 2  carried in the extended LDP message, a network device for executing VLAN mapping. During establishment of the PW  2  in the reverse direction, the PE  1  at an egress end sends an extended LDP message that carries V 1  to the PE  2  at an ingress end. After receiving the extended LDP message, the PE  2  establishes the PW  2  in the reverse direction and selects, according to local VLAN mapping capability and the V 1  carried in the extended LDP message, a network device for executing VLAN mapping. 
         [0035]    When it is determined according to the V 1  and the V 2  that only one PE out of the PE  1  and the PE  2  has VLAN mapping capability, the PE is selected as the network device for executing VLAN mapping. 
         [0036]    Refer to  FIG. 3 , which is a flowchart of a method for selecting a network device according to a second embodiment of the present invention. Specific steps are as follows: 
         [0037]    Step  201 : A second network device receives a network device selection message sent by a first network device, where the network device selection message contains a VLAN mapping capability identifier and a device identifier of the first network device. 
         [0038]    The first network device and the second network device may be provider edge PE devices on a VPLS network; the first network device may carry the VLAN mapping capability identifier and the device identifier of the first network device by extending a LDP message or a BGP message; and when the device identifier of the first network device is an IP address, the device identifier may be obtained from an IP packet header of the network device selection message, and a specific field does not need to be extended in the network device selection message. 
         [0039]    Step  202 : The second network device selects, according to the VLAN mapping capability identifier, the device identifier, local VLAN mapping capability, and a local device identifier, a network device for executing VLAN mapping. 
         [0040]    The selecting a network device for executing VLAN mapping is completed through automatic negotiation according to the VLAN mapping capability identifier and the device identifiers. For example, as shown in  FIG. 2 , a bidirectional PW needs to be established between a PE  1  and a PE  2  so as to provide an E-Tree service. The bidirectional PW is formed of a PW  1  in a forward direction and a PW  2  in a reverse direction. During establishment of the PW  1  in the forward direction, the PE  2  at an egress end sends an extended LDP message to the PE  1  at an ingress end, where an E-Tree-related sub-TLV (sub TLV) is added in a PW interface parameter TLV (Type-Length-Value) in the extended LDP message, to carry a VLAN mapping capability identifier V 2  and a device identifier Node ID 2  of the PE  2 . After receiving the extended LDP message, the PE  1  establishes the PW  1  in the forward direction and selects, according to local VLAN mapping capability and a local device identifier Node ID 1  as well as the V 2  and Node ID 2  carried in the extended LDP message, a network device for executing VLAN mapping. During establishment of the PW  2  in the reverse direction, the PE  1  at an egress end sends an extended LDP message that carries V 1  and the Node ID 1  to the PE  2  at an ingress end. After receiving the extended LDP message, the PE  2  establishes the PW  2  in the reverse direction and selects, according to local VLAN mapping capability and the Node ID 2  as well as the V 1  and Node ID 1  carried in the extended LDP message, a network device for executing VLAN mapping. 
         [0041]    When it is determined according to the V 1  and the V 2  that both the PE  1  and the PE  2  have VLAN mapping capability, one PE is selected, according to the device identifiers Node ID 1  and Node ID 2 , as the network device for executing VLAN mapping. For example, a selection policy is to select a PE with a smallest device identifier as the network device for executing VLAN mapping; for example, if the NodeID 1  is smaller than the NodeID 2 , the PE  1  is selected to execute VLAN mapping whereas the PE  2  disables a local VLAN mapping function. If Node IDs are not in a numerical form, the Node IDs may be sorted so that a network device, such as a network device corresponding to a front-most Node ID after the sorting, is selected according to a sequence of the device identifiers. 
         [0042]    According to the technical solution provided in the embodiments of the present invention, the bidirectional PW executes VLAN mapping on the same PE device, for example, on the PE  1 . When the PE  1  wants to send an Ethernet frame of the E-Tree service to the PE  2  through the PW  1 , the PE  1  first executes VLAN mapping to map local VLAN identifiers Root 1  and Leaf 1  to VLAN identifiers Root 2  and Leaf 2  of the peer PE  2  respectively, and then sends a packet marked with a VLAN identifier Root 2  or Leaf 2  to the PE  2  through the PW  1 . After receiving the packet, the PE  2  directly forwards the packet to a corresponding Root or Leaf port according to the VLAN identifier Root 2  or Leaf 2 . On the contrary, when the PE  2  sends an Ethernet frame of the E-Tree service to the PE  1  through a PW  2 , the PE  2  directly sends a packet marked with the VLAN identifier Root 2  or Leaf 2  to the PE  1  through the PW  2 . After receiving the packet, the PE  1  first executes VLAN mapping to map the Root 2  or Leaf 2  to the local Root 1  or Leaf 1 , and then forwards the packet to a corresponding Root or Leaf port. Therefore, packets borne on the PW  1  and the PW  2  all carry the Root 2  or Leaf 2 , thereby solving the following problem in the prior art: When PEs separately perform VLAN mapping, four different VLAN identifiers exist on a bidirectional PW, bringing difficulties in service maintenance and detection. 
         [0043]    Refer to  FIG. 4 , which is a block diagram of an apparatus for selecting a network device according to a third embodiment of the present invention. The apparatus specifically includes a receiving module  301  and a selecting module  302 , where: 
         [0044]    the receiving module  301  is configured to receive a network device selection message sent by a first network device, and the network device selection message contains a VLAN mapping capability identifier; and 
         [0045]    the selecting module  302  is configured to select, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. 
         [0046]    The network device selection message may further contain a device identifier of the first network device; and 
         [0047]    accordingly, the selecting module  302  is configured to select, according to the VLAN mapping capability identifier, the device identifier, the local VLAN mapping capability, and a local device identifier, the network device for executing VLAN mapping. 
         [0048]    When it is determined, according to the VLAN mapping capability identifier and the local VLAN mapping capability, that both a local network device and the first network device have VLAN mapping capability, the selecting module is specifically configured to select, according to sizes or a sequence of the device identifier and the local device identifier, a network device for executing VLAN mapping. 
         [0049]    Refer to  FIG. 5 , which is a schematic diagram of a system for selecting a network device according to a fourth embodiment of the present invention. The system includes: 
         [0050]    a first network device  401 , configured to send a network device selection message to a second network device  402 , where the network device selection message contains a VLAN mapping capability identifier of the first network device  401 ; and 
         [0051]    the second network device  402 , configured to receive the network device selection message, and select, according to the VLAN mapping capability identifier and local VLAN mapping capability, a network device for executing VLAN mapping. 
         [0052]    The network device selection message may further contain a device identifier of the first network device; and 
         [0053]    accordingly, the second network device  402  is configured to receive the network device selection message, and select, according to the VLAN mapping capability identifier, the device identifier, the local VLAN mapping capability, and a local device identifier, the network device for executing VLAN mapping. 
         [0054]    The first network device and the second network device may be provider edge PE devices on a VPLS network. The first network device may use an extended LDP message or a BGP message to send the network device selection message to the second network device. 
         [0055]    By using the technical solutions provided in the embodiments of the present invention, because a network device for executing VLAN mapping is selected by using a device selection message, it may be ensured that VLAN mapping is executed for a PW in a forward direction and a PW in a reverse direction on the same PE, thereby solving the following problem in the prior art: When PEs separately perform VLAN mapping, four different VLAN identifiers exist on a bidirectional PW, bringing difficulties in service maintenance and detection. 
         [0056]    Although all the embodiments of the present invention describe negotiation between only two PEs for selecting a network device for executing VLAN mapping, for an E-Tree composed of more PEs, a process of negotiation and selection between any two PEs may still use the technical solutions provided in embodiments of the present invention. 
         [0057]    It should be noted that the relational terms herein such as first and second are used only to differentiate an entity or operation from another entity or operation, and do not require or imply any actual relationship or sequence between these entities or operations. Moreover, the terms “include”, “contain”, and any variation thereof are intended to cover a non-exclusive inclusion. Therefore, a process, method, object, or device that includes a series of elements not only includes these elements, but also includes other elements not specified expressly, or may include inherent elements of the process, method, object, or device. If no more limitations are made, an element limited by “include a/an . . . ” does not exclude other same elements existing in the process, the method, the article, or the device which includes the element. 
         [0058]    A person having ordinary skill in the art should understand that all or a part of the steps in the method embodiments may be implemented by a program instructing relevant hardware. The program may be stored in a computer readable storage medium. When the program is run, the steps in the method embodiments are performed. The storage medium may be any medium capable of storing program codes, such as a ROM, a RAM, a magnetic disk, or an optical disk. 
         [0059]    The foregoing descriptions are merely specific exemplary embodiments of the present invention, but are not intended to limit the protection scope of the present invention. Any variation or replacement readily figured out by the skilled person within the technical scope disclosed in the present invention shall fall within the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.