Abstract:
Disclosed in the present invention is a method for end station address distribution information (ESADI) protocol fast convergence, comprising: when a change occurs in network topology, TRILL (transparent interconnection over lots of links) calculates a unicast encapsulation table; when a designated forwarder for a remote VLAN of a remote routing bridge (RB) included in the unicast encapsulation table is reachable, and when a local RB receives from said remote RB an LSP enabling ESADI function information, the local RB and the remote RB establish a neighbour relationship within a local VLAN, thus achieving ESADI protocol fast convergence. Also disclosed is a device for ESADI protocol convergence and a storage medium.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure generally relates to routing transmission techniques in the field of communications, and more particularly to a fast convergence method, apparatus, and storage medium of an End Station Address Distribution Information (ESADI) protocol. 
       BACKGROUND 
       [0002]    A Transparent Interconnection over Lots of Links (TRILL) protocol is already an international standard protocol. According to the TRILL protocol, layer 3 routing techniques are applied to layer 2 transmission to achieve a large-scale layer 2 cloud. Therefore, an excellent and effective layer 2 broadcast domain may be constructed so as to meet increasing requirements for converged networks or super data centres. The TRILL protocol uses an ESADI protocol as an optional protocol for implementing study of an Media Access Control (MAC) address corresponding to an end address. 
         [0003]    The ESADI protocol is an end address study protocol evolved from an Intermediate System to Intermediate System (ISIS) protocol. According to the ESADI protocol, an ESADI neighbour is established by interaction and negotiation of Link-State Packets (LSP) of the TRILL protocol. Each Routing Bridge (RB) running the ESADI protocol generates an LSP of the ESADI protocol. The LSP carries an MAC address corresponding to an end address which is reachable by the RB, and transmits an MAC address of the RB to the network. During the transmission, an RB which takes a current RB as its neighbour saves the LSP messages of the ESADI protocol of the current RB to form a Link State Data Base (LSDB). Therefore, the current RB may study an end address of the ESADI neighbour through the LSDB. 
         [0004]    The current ESADI protocol just proposes that, establishment of a Virtual Local Area Network (VLAN) or neighbour deletion are indicated by an ESADI protocol enabled label carried in a sub Type-length-value (TLV) of Interested VLANs and Spanning Tree Roots in the LSP in the TRILL protocol. 
         [0005]    However, following problems may arise in practice. The current ESADI protocol requires that, an operation of keeping a Directive Routing Bridge (DRB) alive is performed through a Complete Sequence Numbers Protocol Data Unit (CSNP) message of the ESADI protocol so as to judge the DRB. Here, keeping the DRB alive means that, when an ESADI-CSNP message transmitted by the DRB is received within an RB aging time (the RB aging time is a transmission period, i.e., 30 s, of three ESADI-CSNPs by default; DRB transmits one ESADI-CSNP in 10 s by default), it is judged that the DRB is valid; when the ESADI-CSNP message is not received within the RB aging time due to network topology breaking, an RB being added or deleted or the like, the RB assumes the DRB to be invalid. 
         [0006]    A delay of re-establishing the network topology by the ESADI protocol due to the DRB being invalid, may be up to 1200 seconds (an effective time for reserving the information of an invalid ESADI neighbour), such that the ESADI protocol cannot converge in time. During this period, the network topology has been changed actually, and the LSP of the TRILL protocol still exists in the RB. That is, the RB still preserves an unreachable invalid MAC table term, and the neighbouring RB of the RB is not deleted in time. Then, the DRB of the ESADI transmits the LSP according to the original network topology, which may cause an error in transmission of the LSP. The error further causes the ESADI protocol to fail to select a new DRB in time, and thus correct synchronization of an LSP in the newly split network cannot be guaranteed. 
       SUMMARY 
       [0007]    In view of this, it is desired to provide a fast convergence method, apparatus, and storage medium of an End Station Address Distribution Information (ESADI) protocol in embodiments of the disclosure, so as to at least solve a defect of the current ESADI protocol being unable to converge in time. 
         [0008]    The solutions of the embodiments of the disclosure may be achieved as follows. 
         [0009]    According a first aspect, an embodiment of the disclosure provides a convergence method of an End Station Address Distribution Information (ESADI) protocol. The method includes the following steps: a unicast encapsulation table is computed through a Transparent Interconnection over Lots of Links (TRILL) protocol, when network topology is changed; and a neighbouring relationship between a local Routing Bridge (RB) and a remote RB is established in a local Virtual Local Area Network (VLAN), to achieve fast convergence of the ESADI protocol, when the unicast encapsulation table includes the remote RB as an appointed remote VLAN forwarder which is reachable, and the local RB has received a Link-State Packet (LSP) for enabling ESADI function information from the remote RB. 
         [0010]    According to an embodiment, the unicast encapsulation table including the remote RB as an appointed remote VLAN forwarder which is reachable may include: when an encapsulation table term of the remote VLAN of the remote RB exists in the local RB, the remote RB as the appointed remote VLAN forwarder is reachable. 
         [0011]    According to an embodiment, reception of the LSP having information for enabling an ESADI function from the remote RB by the local RB may include the following step: the local RB receives the LSP from the remote RB. The LSP carries a sub Type-length-value (TLV) of Interested VLANs and Spanning Tree Roots, and fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots indicate that the remote VLAN of the remote RB enables the ESADI function information. 
         [0012]    According to an embodiment, the step of establishing, in a local VLAN, a neighbouring relationship between a local RB and a remote RB, may include the following steps: when the local RB has received the LSP from the remote RB, and the unicast encapsulation table includes the encapsulation table term of the remote VLAN of the remote RB, the local VLAN adds the remote RB to be an ESADI neighbouring RB and issue a MAC table term indicating the remote RB is reachable; otherwise, the local VLAN does not add the remote RB to be an ESADI neighbouring RB or issue a MAC table term indicating the remote RB is reachable. 
         [0013]    According to an embodiment, the step of establishing, in the remote VLAN, a neighbouring relationship between a local RB and a remote RB, may include the following step: when the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried by the LSP indicate that the remote VLAN enabled ESADI function information exists, in case that the remote RB as the appointed remote VLAN forwarder is still reachable, no processing is performed; and in case that the remote RB as the appointed remote VLAN forwarder is not reachable, the remote RB as the ESADI neighbouring RB is deleted from the local VLAN and the reachable MAC table term corresponding to the remote RB is deleted. 
         [0014]    According to an embodiment, the step of establishing, in the remote VLAN, a neighbouring relationship between a local RB and a remote RB, may include the following steps: the local RB deletes the remote RB as the ESADI neighbouring RB, when the local RB founds that the remote VLAN enabled ESADI function information indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots of the LSP of the TRILL protocol is withdrawn, aged or deleted. 
         [0015]    According a second aspect, an embodiment of the disclosure provides a convergence apparatus of an ESADI protocol. The apparatus includes a unicast encapsulation table computing unit and an ESADI protocol convergence unit. 
         [0016]    The unicast encapsulation table computing unit is arranged to compute an unicast encapsulation table through a Transparent Interconnection over Lots of Links (TRILL) protocol, when network topology is changed. 
         [0017]    The ESADI protocol convergence unit is arranged to establish, in a local Virtual Local Area Network (VLAN), a neighbouring relationship between a local Routing Bridge (RB) and a remote RB to achieve fast convergence of the ESADI protocol, when the unicast encapsulation table includes the remote RB as an appointed remote VLAN forwarder which is reachable, and the local RB has received a Link-State Packet (LSP) for enabling ESADI function information from the remote RB. 
         [0018]    According to an embodiment, the ESADI protocol convergence unit may include a first sensing module, a second sensing module, a neighbour module and a routing convergence module. 
         [0019]    The first sensing module is arranged to acquire and sense reachability of the remote RB as the appointed remote VLAN forwarder in the TRILL protocol. 
         [0020]    The second sensing module is arranged to acquire and sense whether the remote RB enables the ESADI function information in the VLAN, wherein, the ESADI function information is obtained from the VLAN indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the LSP from the remote RB. 
         [0021]    The neighbour module is arranged to obtain a condition for establishing an ESADI neighbouring relationship from the first sensing module and the second sensing module, and compute and determine the neighbouring relationship. 
         [0022]    The routing convergence module is arranged to add or delete the MAC table term indicating the remote RB is reachable corresponding to the neighbouring relationship through establishing or deleting the neighbouring relationship in the neighbour module, so as to achieve fast convergence of the ESADI protocol. 
         [0023]    According to an embodiment, the first sensing module may include a first sensing device. 
         [0024]    The first sensing device is arranged to sense that the remote RB as the appointed remote VLAN forwarder is reachable, when an encapsulation table term of the remote VLAN of the remote RB exists in the local RB. 
         [0025]    According to an embodiment, the second sensing module may include a second sensing device. 
         [0026]    The second sensing device is arranged to sense that the local RB receives the LSP from the remote RB, wherein the LSP carries the sub Type-length-value (TLV) of Interested VLANs and Spanning Tree Roots, and fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots indicate that the remote VLAN of the remote RB enables the ESADI function information. 
         [0027]    According to an embodiment, the neighbour module may include a neighbour device. 
         [0028]    The neighbour device is arranged to: when fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the LSP received, by the local RB, from the remote RB indicate that the remote VLAN of the remote RB enables the ESADI function information, add the remote RB to be the ESADI neighbouring RB and issues a MAC table term indicating the remote RB is reachable; otherwise, the local VLAN does not add the remote RB to be an ESADI neighbouring RB or issue an MAC table term indicating the remote RB is reachable. 
         [0029]    According to an embodiment, the routing convergence module may include a first routing convergence device and a second routing convergence device. 
         [0030]    The first routing convergence device is arranged to: when the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried by the LSP in the TRILL protocol indicate that the remote VLAN enabled ESADI function information exists, perform no processing, in case that the remote RB as the appointed remote VLAN forwarder is still reachable; and delete the remote RB as the ESADI neighbouring RB from the local VLAN, and delete the reachable MAC table term corresponding to the remote RB, in case that the remote RB as the appointed remote VLAN forwarder is not reachable. 
         [0031]    The second routing convergence device is arranged to delete, by the local RB, the remote RB as the ESADI neighbouring RB, when the local RB founds that the remote VLAN enabled ESADI function information indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots of the LSP of the TRILL protocol is withdrawn, aged or deleted. 
         [0032]    According to a third aspect, an embodiment of the disclosure provides a readable storage medium storing executable instructions. The executable instructions are adapted to perform the convergence method of the ESADI protocol according to the embodiment of the first aspect. 
         [0033]    According to the convergence method, apparatus and storage medium of the ESADI protocol of the embodiments, when the network topology is changed, the unicast encapsulation table is computed through the TRILL protocol. When the unicast encapsulation table includes the remote RB as the appointed remote VLAN forwarder which is reachable, and the local RB has received the LSP, from the remote RB, for enabling the ESADI function information, the neighbouring relationship between the local RB and the remote RB is established in the local VLAN, so as to achieve fast convergence of the ESADI protocol and update the network topology in time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]      FIG. 1  is a schematic flowchart for implementing a convergence method of an ESADI protocol according to a first embodiment of the present disclosure; 
           [0035]      FIG. 2  is a block diagram of a convergence apparatus of the ESADI protocol according to a second embodiment of the disclosure; 
           [0036]      FIG. 3  is a block diagram of an ESADI protocol convergence unit according to a third embodiment of the disclosure; 
           [0037]      FIG. 4  is a schematic flowchart of the third embodiment of the disclosure; 
           [0038]      FIG. 5  is a schematic diagram of a format of a sub TLV of a current ESADI parameter in the third embodiment of the disclosure; 
           [0039]      FIG. 6  is a schematic diagram of a format of a sub TLV of a modified ESADI parameter according to the third embodiment of the disclosure; 
           [0040]      FIG. 7  is a diagram of a normal network topology according to the third embodiment of the disclosure; and 
           [0041]      FIG. 8  is a diagram of an interrupted network topology according to the third embodiment of the disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0042]    The technical solutions of the present disclosure will be further described in detail, in conjunction with the appended drawings and embodiments. 
       First Embodiment 
       [0043]    In order to solve a defect of the current ESADI protocol being unable to converge in time, the embodiment of the disclosure provides a convergence method of the ESADI protocol. The method is applicable to an RB of which a neighbouring relationship may be changed due to a change in network topology. As shown in  FIG. 1 , the method includes the following steps. 
         [0044]    In step S 101 , a unicast encapsulation table is computed through an TRILL protocol, when the network topology is changed. 
         [0045]    When a network topology is interrupted, an RB is added or is deleted or the like, the unicast encapsulation table is computed through the TRILL protocol, so as to determine reachability of all RBs as appointed remote VLAN forwarders. 
         [0046]    In step S 102 , when the unicast encapsulation table includes a remote RB as an appointed remote VLAN forwarder which is reachable, and the local RB has received an LSP for enabling ESADI function information from the remote RB, a neighbouring relationship between the local RB and the remote RB is established in a local VLAN to achieve fast convergence of the ESADI protocol. 
         [0047]    According to the fast convergence method of the ESADI protocol, when the network topology is changed, a unicast encapsulation table is computed through the TRILL protocol. When the unicast encapsulation table includes the remote RB as the appointed remote VLAN forwarder which is reachable, and the local RB has received the LSP for enabling ESADI function from the remote RB, the neighbouring relationship between the local RB and the remote RB is established in the local VLAN to achieve fast convergence of the ESADI protocol, so as to update the network topology in time. 
         [0048]    Specially, step S 102  of establishing, in a local Virtual Local Area Network (VLAN), a neighbouring relationship between a local Routing Bridge (RB) and a remote RB to achieve fast convergence of the ESADI protocol, when the unicast encapsulation table includes the remote RB as an appointed remote VLAN forwarder is reachable, and the local RB has received a Link-State Packet (LSP) for enabling ESADI function information from the remote RB, may include the following steps. 
         [0049]    In step S 1021 , when an encapsulation table term of the remote VLAN of the remote RB exists in the local RB, the remote RB as the appointed remote VLAN forwarder is reachable. 
         [0050]    In step S 1022 , the local RB receives the LSP from the remote RB. The LSP carries a sub TLV of Interested VLANs and Spanning Tree Roots, and fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots indicate that the remote VLAN of the remote RB enables the ESADI function information. 
         [0051]    In step S 1023 , after the local RB receives the LSP from the remote RB, the local VLAN of the local RB may wait for the remote RB to complete computation of the unicast encapsulation table, instead of adding the remote RB to be an ESADI neighbouring RB immediately. When the unicast encapsulation table includes the encapsulation table term of the remote VLAN of the remote RB, the local VLAN adds the remote RB to be the ESADI neighbouring RB and issues a MAC table term indicating the remote RB is reachable. Otherwise, the local VLAN does not add the remote RB to be an ESADI neighbouring RB or issue an MAC table term indicating the remote RB is reachable. 
         [0052]    In step S 1024 , when the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried by the LSP of the TRILL protocol indicate that the remote VLAN enabled ESADI function information exists, in case that the remote RB as the appointed remote VLAN forwarder is still reachable no processing is performed; and in case that the remote RB as the appointed remote VLAN forwarder is not reachable, the remote RB as the ESADI neighbouring RB is deleted from the local VLAN, and the reachable MAC table term corresponding to the remote RB is deleted. 
         [0053]    In step S 1025 , when the local RB founds that the remote VLAN enabled ESADI function information indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots of the LSP of the TRILL protocol is withdrawn, aged or deleted, the local RB deletes the remote RB as the ESADI neighbouring RB. 
       Second Embodiment 
       [0054]    The second embodiment and the first embodiment are based on a same inventive concept. The second embodiment provides a convergence apparatus of the ESADI protocol. As shown in  FIG. 2 , the apparatus includes a unicast encapsulation table computing unit  201  and an ESADI protocol convergence unit  202 . 
         [0055]    The unicast encapsulation table computing unit  201  is arranged to compute the unicast encapsulation table through the TRILL protocol, when the network topology is changed. 
         [0056]    The ESADI protocol convergence unit  202  is arranged to establish, in a local Virtual Local Area Network (VLAN), a neighbouring relationship between a local Routing Bridge (RB) and a remote RB to achieve fast convergence of the ESADI protocol, when the unicast encapsulation table includes the remote RB as an appointed remote VLAN forwarder which is reachable, and the local RB has received a Link-State Packet (LSP) for enabling ESADI function information from the remote RB. 
         [0057]    Specially, as shown in  FIG. 3 , the ESADI protocol convergence unit  202  may include a first sensing module  2021 , a second sensing module  2022 , a neighbour module  2023 , and a routing convergence module  2024 . 
         [0058]    The first sensing module  2021  is a sensing module for sensing the reachability of the remote appointed forwarder, and is arranged to acquire and sense the reachability of the remote RB as the appointed remote VLAN forwarder in the TRILL protocol. The first sensing module  2021  may include a first sensing device. The first sensing device is arranged to sense that the remote RB as the appointed remote VLAN forwarder is reachable, when an encapsulation table term of the remote VLAN of the remote RB exists in the local RB. 
         [0059]    The second sensing module  2022  is arranged to acquire and sense whether the remote RB enables the ESADI function information in the VLAN. The ESADI function information is acquired from the VLAN indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the LSP of the TRILL protocol from the remote RB. The second sensing module  2022  includes a second sensing device arranged to sense that the local RB receives the LSP from the remote RB. The LSP carries the sub Type-length-value (TLV) of Interested VLANs and Spanning Tree Roots, and fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots indicate that the remote VLAN of the remote RB enables the ESADI function information. 
         [0060]    The neighbour module  2023  is arranged to obtain two conditions for establishing an ESADI neighbouring relationship from the first sensing module and the second sensing module respectively, and decide to establish or delete the neighbouring relationship. The neighbour module  2023  includes a neighbour device. The neighbour device is arranged to perform the following steps. When fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the LSP received, by the local RB, from the remote RB indicate that the remote VLAN of the remote RB enables the ESADI function information, the neighbour device waits for the remote RB to complete computation of the unicast encapsulation table, instead of adding the remote RB to be an ESADI neighbouring RB immediately. When the unicast encapsulation table includes the encapsulation table term of the remote VLAN of the remote RB, the local VLAN adds the remote RB to be the ESADI neighbouring RB and issues a MAC table term indicating the remote RB is reachable. Otherwise, the local VLAN does not add the remote RB to be an ESADI neighbouring RB or issue an MAC table term indicating the remote RB is reachable. 
         [0061]    The routing convergence module  2024  is arranged to add or delete the MAC table term indicating the remote RB is reachable corresponding to a neighbouring relationship through establishing or deleting the neighbouring relationship in the neighbour module, so as to achieve fast convergence of the ESADI protocol. The routing convergence module  2024  may include a first routing convergence device and a second routing convergence device. 
         [0062]    The first routing convergence device is arranged to, when the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried by the LSP in the TRILL protocol indicate that the remote VLAN enabled ESADI function information exists, perform no processing in case that the remote RB as the appointed remote VLAN forwarder is still reachable, and delete the remote RB as the ESADI neighbouring RB from the local VLAN and delete the reachable MAC table term corresponding to the remote RB in case that the remote RB as the appointed remote VLAN forwarder is not reachable. 
         [0063]    The second routing convergence device is arranged to delete, by the local RB, the remote RB as the ESADI neighbouring RB, when the local RB founds that the remote VLAN enabled ESADI function information indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots of the LSP of the TRILL protocol is withdrawn, aged or deleted. 
       Third Embodiment 
       [0064]    According to the third embodiment, the unicast encapsulation table is computed based on the appointed remote forwarder indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried by the LSP in the TRILL protocol, and the neighbouring relationship is maintained based on dynamic reachability of unicast encapsulation information included in the unicast encapsulation table. Therefore, an ESADI neighbour may be established or deleted rapidly in response to a change in the network topology, an invalidity of an DRB may be detected rapidly, a unified and new DRB may be selected and LSP synchronization of ESADI may be accelerated, so as to improve the convergence performance of the ESADI protocol. 
         [0065]    As shown in  FIG. 4 , the flowchart of the embodiment includes the following steps. 
         [0066]    In Step S 401 , whether the remote RB enables the ESADI function information in the VLAN is acquired and sensed, from the remote VLAN enabled ESADI information indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the LSP of the TRILL protocol. 
         [0067]    In step S 402 , the reachability of the RB as the appointed remote VLAN forwarder in the TRILL protocol is acquired and sensed. 
         [0068]    In step S 403 , a neighbour is added or deleted. In case that both step S 101  and step S 102  are completed successfully, the neighbour is added; otherwise, the neighbour is deleted. 
         [0069]    In step S 404 , an ESADI routing converges. When the neighbouring RB is added, an MAC table term indicating the neighbouring RB is reachable is added. When the neighbouring RB is deleted, an MAC table term indicating the neighbouring RB is reachable is deleted. 
         [0070]    Here, The ESADI protocol is mainly responsible for studying a reachable MAC address of the remote RB to form an TRILL MAC table in the local RB, after establishing a ESADI neighbouring relationship between the local RB and remote RB. The TRILL MAC table is used to judge which remote RB an Ethernet frame can be unicasted to, based on MAC and VLAN information of the Ethernet frame. 
         [0071]    Conventionally, the unicast encapsulation table is used to encapsulate a normal Ethernet frame into an unicast TRILL data message and provides information required for head information for encapsulating the TRILL message. Specially, when an Ethernet frame is received, the TRILL MAC table of the local RB formed by the ESADI protocol is searched for based on the MAC and VLAN information of the Ethernet frame. When the Ethernet frame is to be unicasted to a certain remote RB, the Ethernet frame is encapsulated into an TRILL data message through head information for encapsulating the TRILL message based on the unicast encapsulation table, and the TRILL data message is transmitted to the remote RB finally. 
         [0072]    Here, unicast encapsulation table computation includes TRILL network unicast topology computation, and unicast encapsulation table filling. 
         [0073]    1) TRILL Network Unicast Topology Computation 
         [0074]    An SPF algorithm is performed by taking the local RB as a root. The SPF algorithm assumes each router to be a root and computes a distance between the router and each remote RB. Each RB may compute a topology graph of a routing domain based on a unified data base. The topology graph is similar to a tree called a shortest path tree, i.e., an STP tree. When it is found that a remote RB exists in the STP tree, topology reachability from the local RB to the remote RB is asserted. 
         [0075]    2) Unicast Encapsulation Table Filling 
         [0076]    In case that the remote RB is reachable topologically, a unicast encapsulation table of a corresponding VLAN is filled in, based on the appointed remote VLAN forwarder notified by the remote RB in the sub TLV of the Interested VLANs and Spanning Tree Roots. 
         [0077]    The ESADI protocol serves for unicasting in the TRILL network. A data message is unicasted in the TRILL network based on the unicast encapsulation table. The fact that the unicast encapsulation table of the VLAN is not formed, means there is no remote RB as a receiver of the VLAN. Therefore, the ESADI neighbouring RB should be formed under the condition that the unicast encapsulation table of the VLAN is formed, i.e., the TRILL network has unicast reachability to the remote RB. In contrast, in a case that the unicast encapsulation table of the VLAN is not formed while the ESADI neighbouring RB of the VLAN is created, study of MAC reachability information of the ESADI becomes useless. 
         [0078]    In practice, the third embodiment may include the following aspects. 
         [0079]    I Modification of the ESADI Protocol 
         [0080]    1. Modification of DRB Failure Process 
         [0081]    According to the original protocol, it is proposed that an DRB is kept alive based on an CSNP message of the ESADI. When a RB receives an ESADI-CSNP message from the DRB within one RB aging time period, the DRB is assumed to be valid and the aging time period is refreshed to be 30 seconds. When the RB fails to receive the ESADI-CSNP message from the DRB within the RB aging time period, the DRB is assumed to be invalid, and the RB may transmit, as a proxy of the DRB function, the CSNP message. 
         [0082]    The embodiment eliminates the above process. According to the processing method provided by the embodiment, a change in the network topology may be responded rapidly and the failure of the DRB may be detected rapidly. Then, a new DRB is selected from valid neighbouring RBs and implements the DRB function to transmit the CSNP message. 
         [0083]    2. Modification of the Sub TLV of a ESADI Parameter 
         [0084]    As shown in  FIG. 5 , a sub TLV of a current ESADI parameter includes: a DRB selection priority level, a CSNP timeout period, a flag bit (currently, the flag bit merely includes a bit indicating whether unicast is supported), an extension field and the like. 
         [0085]    As shown in  FIG. 6 , a field of ‘CSNP Time’ corresponding to the CSNP timeout period in the sub TLV of the ESADI parameter required in the protocol (or draft) is deleted, and the modified sub TLV includes the DRB selection priority, a flag bit (currently, the flag bit includes a bit indicating whether unicast is supported), and an extension field. 
         [0086]    2) Processing Method 
         [0087]    1. When the local RB has received the appointed remote forwarder indicated in the fields of ‘nickname’ and ‘VLAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the TRILL-LSP message from the remote RB, the local RB may perform computation of the unicast encapsulation table on the sub TLV of the remote RB, instead of immediately adding the VLAN of the remote RB to make the remote RB to be a ESADI neighbouring RB. When the remote RB as the appointed remote VLAN forwarder is reachable, that is, there is an encapsulation table term of the VLAN of the remote RB, the remote RB is added to be an ESADI neighbouring RB and a MAC table term indicating the remote RB is reachable is issued. Otherwise, the remote RB will not be added to be an ESADI neighbouring RB and a MAC table term indicating the remote RB is reachable will not be issued. 
         [0088]    2. In case that there is the appointed remote forwarder indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the TRILL-LSP message, when the TRILL protocol founds that the network topology is changed, the computation of the unicast encapsulation table is performed on the sub TLV. In case that the remote RB as the appointed VLAN forwarder is still reachable, no processing is performed. Otherwise, the ESADI neighbouring RB is deleted and the MAC table term indicating the remote RB is reachable is deleted. 
         [0089]    3. When the appointed remote forwarder information indicated in the fields of ‘nickname’ and ‘A/LAN’ in the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the TRILL-LSP message from the remote RB is deleted, withdrawn or aging, the remote RB as the neighbouring RB is deleted. 
         [0090]    4. The ESADI neighbouring RB may added or deleted directly through the methods of the above ‘1’, ‘2’, and ‘3’. In this case, DRB selection in the ESADI protocol may be triggered immediately. The selection is performed among current ESADI neighbouring RBs. Therefore, a new DRB may replace an old DRB immediately, to transmit the CSNP message periodically. In this way, the failure of the DRB may be responded more rapidly, and the synchronization of the LSP data base may be accelerated after the DRB fails, so as to improve convergence performance of the network. 
         [0091]    In order to make the object, technical methods and advantages of the disclosure to be clearer, the method of the disclosure will be described in detail, and the disclosure will be described in detail in conjunction with the appended drawings. 
         [0092]    First Sub-Instance 
         [0093]    As shown in  FIG. 7 , an RB 1 , an RB 2 , an RB 3  and an RB 4  form a linear network topology. Each of the RB 1 , the RB 2 , the RB 3  and the RB 4  is a boundary RB of an TRILL network. Each RB has a physical interface which is within a VLAN 1  and connected to a local host. Therefore, each RB becomes an appointed VLAN 1  forwarder, and enables the ESADI protocol. Priority levels of the RB 1 , the RB 2 , the RB 3  and the RB 4  are 126, 64, 64 and 127 respectively. 
         [0094]    It is assumed that only the RB 1 , the RB 2  and the RB 3  exist in the original network topology, and each of them establishes an ESADI neighbour within the VLAN 1 . At this time, the RB 4  accesses the TRILL network newly. Since the RB 4  has a local interface for accessing the VLAN 1 , the RB 4  becomes one appointed VLAN 1  forwarder with this interface and enables the ESADI protocol. Then, the RB 4  issues, by the LSP of the TRILL protocol, that the RB 4  supports the ESADI protocol in the VLAN 1 . That is, the RB 4  fills a sub TLV of the Interested VLANs and Spanning Tree Roots into the LSP of the TRILL protocol, so as to notify the VLAN 1  that it supports the ESADI protocol and the RB 4  is an appointed VLAN 1  forwarder. 
         [0095]    After flooding of the LSP by the RB 4 , the RB 1 , the RB 2  and the RB 3  may receive the LSP of the TRILL protocol generated in the RB 4 . Meanwhile, the RB 4  may receive LSPs of the TRILL protocols generated by the RB 1 , the RB 2  and the RB 3  respectively, so as to reach a synchronization state of the LSPs. 
         [0096]    When the RB 1  receives the LSP from the RB 4 , the RB 1  may extract the ‘nickname’ and ‘A/LAN’ of the RB 4  from the sub TLV of the Interested VLANs and Spanning Tree Roots carried in the LSP of the RB 4 , to compute the unicast encapsulation table. It is found that the ‘nickname’ and ‘VLAN 1 ’ of the RB 4  is reachable, that is, there is an encapsulation table term of the VLAN of the RB 4 , and thus the RB 4  is added to be an ESADI neighbour in an ESADI neighbour list. 
         [0097]    The addition of the new neighbour triggers the selection of DRB of the ESADI. At this time, the RB 1 , the RB 2  and the RB 3  have not received the ESADI-LSP from the RB 4  yet. The RB 1 , the RB 2  and the RB 3  assume the DRB selection priority level of the RB 4  to be 64 by default. Assuming that the RB 1  has the highest priority level of 126, the RB 1  is assumed to be the DRB and transmit the ESADI-CSNP periodically. It should be noted that, since flooding path of the ESADI-LSP generated by the RB 4  is RB 3 -RB 2 -RB 1 , a neighbouring relationship will be established between the RB 3  and the RB 4  firstly, and thereafter, a neighbouring relationship will be established between the RB 2  and the RB 4 . After the neighbouring relationship is established between the RB 3  and the RB 4  firstly, the RB 3  may receive the ESADI-LSP from the RB 4  firstly, and find the DRB selection priority level of the RB 4  is 127. Therefore, the RB 4  is selected to be the DRB of the ESADI. At this time, there is inconsistence with respect to the LSP on the network topology. That is, the RB 1  and the RB 2  assume the DRB to be RB 1  and the RB 3  and RB 4  assume the DRB to be RB 4 . However, this will not affect the synchronization of the ESADI-LSP. The ESADI protocol requires that an ESADI-CNSP should be normally processed even if the ESADI-CNSP is not generated from the DRB, so as to facilitate the synchronization of the ESADI-LSP. Finally, each of the RB 1 , the RB 2  and the RB 3  will receive the ESADI-LSP generated from the RB 4 . 
         [0098]    Second Sub-Instance 
         [0099]    As shown in  FIG. 8 , the RB 1 , the RB 2 , the RB 3  and the RB 4  form a linear network topology. Each of the RB 1 , the RB 2 , the RB 3  and the RB 4  is an edge RB, and has a physical interface which is within the VLAN 1  and connected to a local host. Therefore, each RB becomes an appointed VLAN 1  forwarder and enables the ESADI protocol. The priority levels of the RB 1 , the RB 2 , the RB 3  and the RB 4  are 126, 64, 64 and 127 respectively. It is assumed that a link between the RB 2  and the RB 3  is interrupted. The second sub-instance will be described by taking the RB 1  and RB 4  as description objects. 
         [0100]    In case that the link between the RB 2  and the RB 3  is interrupted, the RB 1  may find this fault occurs through the LSP of the TRILL protocol. Thereby, an unicast topology from the RB 1  to the RB 4  is interrupted. By means of the computation of the unicast encapsulation table, it is found that the ‘nickname’ and ‘VLAN 1 ’ of the RB 4  are not reachable any longer. That is, the RB 4  as appointed VLAN 1  forwarder is unicast unreachable. Although the TRILL-LSP of the RB 4  still exists in the RB 1 , which indicates that the RB 4  enables the ESADI in the VLAN 1 , the ESADI neighbouring relationship between the RB 1  and the RB 4  may be deleted immediately in the RB 1 , without the need of deleting the neighbouring relationship after the aging time period (1200 seconds) of the TRILL-LSP of the RB 4 . 
         [0101]    Since the RB 4  as an ESADI neighbour is deleted from the RB 1 , the DRB selection is triggered. At this time, the RB 1  has only one ESADI neighbour, i.e., the RB 2 , and the DRB will be selected from the RB 2  and the RB 1 . At this time, the RB 1  has a higher priority level, and thus will be selected to be the DRB of the ESADI and transmit the ESADI-CSNP periodically. 
         [0102]    Meanwhile, Since the RB 4  as the ESADI neighbour is deleted from the RB 1 , the reachable MAC address of the RB 4  as the ESADI neighbour in the RB 1  may be deleted immediately, and the RB 1  does not have an invalid MAC address no longer. Therefore, the problem that a local message in the TRILL of the MAC address on the RB 4  cannot be transmitted after the local message is subjected to unicast encapsulation, will not arise. In addition, discarding the local message due to the above problem finally may cause a waste of forwarding resources. According to this embodiment, the local message with an unknown unicast reachability is encapsulated into a TRILL broadcast within the VLAN 1 . Then, the local message attempts to reach an MAC address of the RB 4 . Although the broadcast message cannot reach the MAC address, an opportunity to reattempt and study is provided. Therefore, other unicast forwarding ways may be studied once there are other reachable paths. 
         [0103]    According to the fast convergence method of the ESADI protocol provided by the embodiment, the LSP is generated through the TRILL protocol, when an ESADI neighbouring relationship with respect to the local RB is changed. The RB performs the unicast encapsulation computation after the RB receives the LSP, to obtain a remote RB relationship list of the local RB. The local RB transmits the remote RB relationship list of the local RB to a next-level ESADI neighbouring RB, and updates remote RB relationship list of the local RB based on a remote RB relationship list of the next-level ESADI neighbouring RB. Therefore, the problem caused by the method in which the current ESADI protocol detects a change in the network topology through a keep-alive time period of the DRB, can be avoided. The delay of 1200 seconds due to the aging time period of the TRILL-LSP is omitted, so as to achieve the fast convergence of the ESADI protocol. 
         [0104]    Based on the fast convergence method of the ESADI protocol provided by the above embodiments, this embodiment provides a switch applied in the TRILL network. The switch includes a memory and a processor connected to the memory. 
         [0105]    The memory is adapted to store instructions, which, when executed by the processor, cause the processor to perform the following steps: when the network topology is changed, the unicast encapsulation table is computed through the TRILL protocol; when the unicast encapsulation table includes a remote RB as an appointed VLAN forwarder which is reachable, and the local RB has received an LSP, from the remote RB, for enabling the ESADI function information, a neighbouring relationship between the local RB and the remote RB is established in the local VLAN, to achieve fast convergence of the ESADI protocol. 
         [0106]    The unicast encapsulation table computing unit and the ESADI protocol convergence unit included in the convergence apparatus of the ESADI protocol provided by the embodiment of the disclosure, and the first sensing module, the second sensing module, the neighbour module, and the routing convergence module included in the ESADI protocol convergence unit, may be implemented in the processor of the switch, or may be implemented in a specific logic circuit. In practice, the processor may be a Central Processing Unit (CPU), a microprocessor (MPU), a digital signal processor (DSP), a field programmable gate array (FPGA) or the like. 
         [0107]    According to the embodiment of the disclosure, the convergence method of the ESADI protocol, when implemented in a form of a software function module and sold or used as a standalone product, may be stored in a readable storage medium. In view of this, essence or the contribution to the related art of the technical solutions of the embodiments of the disclosure may be embodied in a software product. The software product is stored in a storage medium and includes several instructions which cause a computer device (may be a personal computer, a server, a network device or the like) to perform some or all of the method according to an embodiment of the disclosure. The storage medium may include an USB driver, a removable hard disk, a Read-Only Memory (ROM), a magnetic disk or an optical disk or other mediums which can store program codes. Therefore, the embodiment of the disclosure is not limited to any specific combination of software and hardware. 
         [0108]    Correspondingly, the embodiment of the disclosure may further provide a readable storage medium storing executable instructions for performing any one of the convergence methods of the ESADI protocol according to the embodiments of the disclosure. 
         [0109]    It should be understood that, in the embodiments of the disclosure, the disclosed method and apparatus may be implemented in other ways. The apparatus described above is merely exemplary. For example, the division of the units is merely a logic division, and in practice, may have other divisions. For example, multiple units or assemblies may be combined or integrated into another system, and some features may be omitted or not implemented. In additional, coupling, direct coupling or communication connection between the shown or discussed components may be implemented via some interfaces, apparatus or units, and may be electrical, mechanical or other forms. 
         [0110]    The units explained as separate components may be physically separated from each other or not. A component shown as a unit may be a physical unit or not, that is, may be located at one place or may be distributed over multiple network units. Some or all of the units may be selected as required to achieve the object of the technical solution of the embodiment. 
         [0111]    In additional, the functional units of the embodiments of the disclosure may be integrated in a single processing unit, or may be each implemented as a single unit. Two or more of the functional units may be integrated in a single processing unit. The integrated unit may be implemented in hardware or may be implemented in hardware and software. 
         [0112]    The skilled in the art should understand that, some or all of steps for implementing the embodiment of the method may be performed via hardware related to a program which may be stored in a computer-readable storage medium. The program, when executed, performs the steps of the embodiment of the method. The storage medium may include a removable storage device, a Read-Only Memory (ROM), a magnetic disk or an optical disk or other mediums which can store program codes. 
         [0113]    The described above are merely embodiments of the disclosure, and the disclosure is not limited thereto. Modifications or replacements without departing from the scope of the disclosure, easily envisaged by the skilled in the art, may fall within the protection scope of the disclosure. 
       INDUSTRIAL APPLICABILITY 
       [0114]    According to the embodiment of the disclosure, when network topology is changed, the unicast encapsulation table is computed through the TRILL protocol. When the unicast encapsulation table includes the remote RB as an appointed remote VLAN forwarder which is reachable, and the local RB has received an LSP for enabling ESADI function information from the remote RB, a neighbouring relationship between the local RB and the remote RB is established in the local VLAN, to achieve fast convergence of the ESADI protocol. Therefore, correct synchronization of an LSP in the newly split network can be guaranteed.