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US-12627596-B2 - Method and apparatus for designated router seamless switchover

US12627596B2US 12627596 B2US12627596 B2US 12627596B2US-12627596-B2

Abstract

Embodiments of the present disclosure provide method and apparatus for Designated Router (DR) seamless switchover. A method performed by a network device comprises detecting a DR failure event due to a failure DR. The method further comprises detecting that the second edge device is unreachable. The method further comprises holding refresh of router-Link State Advertisements (router-LSA) in a link-state database and flooding procedure, when a Backup Designated Router (BDR) has not declared to be a working DR in an Open Shortest Path First (OSPF) network.

Inventors

  • Wei Xu
  • Shuxia TAI
  • Huajie GUO
  • Lei Zhou

Assignees

  • TELEFONAKTIEBOLAGET LM ERICSSON (PUBL)

Dates

Publication Date
20260512
Application Date
20210915

Claims (20)

  1. 1 . A method performed by a network device comprising: detecting a designated router (DR) failure event; and after detecting the designated router failure event and when a backup designated router (BDR) has not declared to be a working designated router, (i) refraining from refreshing router-Link State Advertisements (LSA) in a link-state database and (ii) refraining from performing a flooding procedure.
  2. 2 . The method of claim 1 , wherein the flooding procedure comprises flooding at least one LSA message to at least one neighbor network device.
  3. 3 . The method of claim 1 , wherein the DR failure event comprises at least one of: Failure event trigged by open shortest path first (OSPF) hello mechanism; Failure event trigged by Bidirectional Forwarding Detection (BFD) session down.
  4. 4 . The method of claim 1 , wherein the network device is in an open shortest path first (OSPF) network, the OSPF network comprising at least one of: OSPF Broadcast network; OSPF Non-Broadcast Multiple Access network.
  5. 5 . The method of claim 1 , further comprising: removing at least one routing entry whose next hop is the failure DR in a routing table.
  6. 6 . The method of claim 1 , further comprising: starting a timer to wait for the BDR declared to be the working DR.
  7. 7 . The method of claim 1 , further comprising: receiving a network-LSA message from a working DR.
  8. 8 . The method of claim 6 , further comprising: stopping the timer when a network-LSA message is received from the working DR.
  9. 9 . The method of claim 1 , further comprising: refraining from performing a route calculation to prevent update of the routing table.
  10. 10 . The method of claim 6 , further comprising: refreshing router-LSA in the link-state database and performing the flooding procedure when the timer is stopped or expired.
  11. 11 . The method of claim 9 , further comprising: performing the route calculation; updating the routing table.
  12. 12 . The method of claim 1 , wherein the network device is a DR-Other router or a server with DR-Other function.
  13. 13 . A method performed by a network device, when a network-Link State Advertisement (LSA) message is received or a timer is expired, the method comprises: refreshing router-LSA in a link-state database; and performing a flooding procedure, wherein the refreshing router-LSA in the link-state database and performing the flooding procedure have been refrained from due to a designated router (DR) failure event.
  14. 14 . The method of claim 13 , wherein the flooding procedure comprises flooding at least one LSA message to at least one neighbor network device.
  15. 15 . The method of claim 13 , wherein the network-LSA message is received from the working DR.
  16. 16 . The method of claim 13 , wherein the network device is in an open shortest path first (OSPF) network, the OSPF network comprising at least one of: OSPF Broadcast network; OSPF Non-Broadcast Multiple Access, NBMA network.
  17. 17 . The method of claim 13 , the method further comprising: performing a route calculation; updating a routing table.
  18. 18 . The method of claim 13 , further comprising: detecting a DR failure event; after detecting the DR failure event and when a backup designated router (BDR) has not been declared to be a working designated router, (i) refraining from refreshing router-Link State Advertisements (LSA) in a link-state database and (ii) refraining from performing a flooding procedure.
  19. 19 . The method of claim 18 , wherein the DR failure event comprises at least one of: Failure event trigged by open shortest path first (OSPF) hello mechanism; Failure event trigged by Bidirectional Forwarding Detection (BFD) session down.
  20. 20 . A network device, comprising: one or more processors; and one or more memories comprising computer program codes, the one or more memories and the computer program codes configured to, with the one or more processors, cause the network device at least to perform: detecting a designated router (DR) failure event; and after detecting the designated router failure event and when a backup designated router (BDR) has not been declared to be a working designated router, (i) refraining from refreshing router-Link State Advertisements (LSA) in a link-state database and (ii) refraining from performing a flooding procedure.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is a 35 U.S.C. § 371 National Stage of International Patent Application No. PCT/CN2021/118512, filed 2021 Sep. 15. TECHNICAL FIELD The non-limiting and exemplary embodiments of the present disclosure generally relate to the technical field of communications, and specifically to methods and apparatuses for designated router seamless switchover. BACKGROUND This section introduces aspects that may facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art. Request For Comments (RFC) 2328, STD 54, April 1998, describes the specification of the Open Shortest Path First (OSPF) internet routing protocol. OSPF is classified as an Interior Gateway Protocol (IGP). This means that it distributes routing information between routers belonging to a single Autonomous System. The OSPF protocol is based on link-state or Shortest Path First (SPF) technology. Each OSPF broadcast network or OSPF Non-Broadcast Multiple Access (NBMA) network have a Designated Router (DR). DR becomes adjacent to all other routers on the network. Since the link state databases are synchronized across adjacencies, the DR plays a central part in the synchronization process. Sometimes, DR failure happens in the network. In order to make the transition to a new DR smoother, there is a Backup Designated Router (BDR) for each broadcast and NBMA network. The BDR is also adjacent to all routers on the network, and becomes Designated Router when the previous DR fails. SUMMARY This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. In OSPF network, network device proceeds DR and BDR election process. This process is used to calculate DR and BDR of a network. The calculation result is as follows. If the network device is chosen as DR, then its new interface state is DR. If the network device is chosen as BDR, then its new interface state is Backup. Otherwise, its new interface state is DR Other. If the interface state of a network device is DR Other, we call the network device DR-Other device. The detailed election process could reference section 9.4 Electing the Designated Router in the RFC 2328. When DR failure happens in the network, all DR-Other devices can't compute routes successfully in time before BDR declared to be the working DR. The traffic drop consequently happens during the period of DR switchover. The switchover time may take seconds or even longer in large scale networks to complete topology convergency. To overcome the above mentioned problem, the embodiments of the present disclosure proposes a DR seamless switchover method. In a first aspect of the disclosure, there is provided a method performed by a network device. The method comprises detecting a DR failure event due to a failure DR. The method further comprises holding refresh of router-Link State Advertisements (router-LSA) in a link-state database and flooding procedure, when a BDR has not declared to be a working DR in an OSPF network. In an embodiment, the flooding procedure comprises flooding at least one LSA message to at least one neighbor network device. In an embodiment, the DR failure event comprises at least one of: Failure event trigged by OSPF hello mechanism, and Failure event trigged by Bidirectional Forwarding Detection (BFD) session down. In an embodiment, the method further comprises removing at least one routing entry whose next hop is the failure DR in a routing table. In an embodiment, the method further comprises starting a timer to wait for the BDR declared to be the working DR. In an embodiment, the method further comprises receiving a network-LSA message from a working DR. In an embodiment, the method further comprises stopping the timer when a network-LSA message is received from the working DR. In an embodiment, the method further comprises holding route calculation to prevent update of the routing table. In an embodiment, the method further comprises refreshing router-LSA in the link-state database and proceeding with the flooding procedure when the timer is stopped or expired. In an embodiment, the method further comprises proceeding with route calculation. The method further comprises updating the routing table. In an embodiment, the network device is a DR-Other router or a server with DR-Other function. In a second aspect of the disclosure, there is provided a method performed by a network device, when a network-Link State Advertisement (network-LSA) message is received or a timer is expired. The method comprises refreshing router-LSA in a link-state database