OSPF backup interface

• US 20020078232A1
• Filed: 12/20/2000
• Published: 06/20/2002
• Est. Priority Date: 12/20/2000
• Status: Active Grant

• Current Assignee: RPX Clearinghouse LLC (RPX Corporation)
• Original Assignee: Nortel Networks Limited (Nortel Networks Corporation)
• Inventors: Sultan, Nevein T., Simpson, Valerie A., Jamieson, Dwight D.
• Granted Patent: US 7,234,001 B2
• Time in Patent Office: Days
• US Class Current: 709/238
• CPC Class Codes: H04L 45/04 Interdomain routing, e.g. hierarchical routing
• CPC Class Codes: H04L 45/22 Alternate routing
• CPC Class Codes: H04L 45/28 using route fault recovery

Abstract

A method and apparatus provides protection against resource failures in Open Shortest Path First (OSPF) networks, without increasing the complexity of the network topology and/or management. An internal router (IR) automatically maintains a back-up link in a dormant state until a network failure affecting communications with a primary adjacent area border router (ABR) is detected. Upon detection of the network failure, the IR activates the back-up link in order to enable traffic flow to an alternate adjacent ABR, which by-passes the network failure. Upon recovery of communications with the primary adjacent ABR, the IR automatically deactivates the back-up link and resumes traffic flow through the primary adjacent ABR. As a result, traffic is forwarded into the back-up link only when communications with the primary adjacent ABR has failed, thereby maintaining simplicity in the network topology, and minimizing network management and administration requirements.

Claims

1. A method of protecting an Open Shortest Path First (OSPF) network against network failures affecting traffic flow between an interior router (IR) and a predetermined primary area border router (ABR) using a back-up link between the IR and a predetermined alternate ABR, the method comprising steps of:

maintaining the back-up link in a dormant state during normal operations of the network, such that no traffic is forwarded to the back-up link during normal operations of the network; and

activating the back-up link in response to a network failure affecting communications between the IP and the primary ABR, such that traffic can be routed between the IR and the alternate ABR through the back-up link.

2. A method as claimed in claim 1, wherein the step of maintaining the back-up link in a dormant state comprises steps of:

assigning a backup interface type attribute to the back-up link; and

controlling each of the IR and the alternate ABR such that;

information respecting the back-up link is not advertised to adjacent routers; and

the back-up link is not identified as a valid route in respective forwarding tables of each of the IR and the alternate ABR.

3. A method as claimed in claim 1, wherein the step of activating the back-up link comprises steps of:

detecting the network failure affecting communications between the IP and the primary ABR;

promoting the back-up link to an active status; and

advertising the back-up link as a valid route.

4. A method as claimed in claim 3, wherein the network failure is detected by the IR.

5. A method as claimed in claim 4, wherein the step of promoting the back-up link to an active status is initiated by the IR.

6. A method as claimed in claim 3, wherein the step of detecting the network failure comprises steps of:

detecting a loss of communications between the IR and the primary ABR;

monitoring a link between the IR and the primary ABR for a predetermined period, to detect recovery of communications; and

declaring a link failure if recovery of communications between the IR and the primary ABR is not detected within the predetermined period.

7. A method as claimed in claim 3, wherein the step of promoting the back-up link comprises a step of negotiating an adjacency relationship between the IR and the alternate ABR.

8. A method as claimed in claim 1, further comprising a step of deactivating the back-up link in response to a network recovery affecting communications between the IP and the primary ABR, such that traffic flow through the back-up link between the IR and the alternate ABR is terminated.

9. A method as claimed in claim 8, wherein the step of deactivating the back-up link comprises steps of:

detecting the network recovery; and

demoting the back-up link to an inactive status.

10. A method as claimed in claim 9, wherein the network recovery is detected by the IR.

11. A method as claimed in claim 10, wherein the step of deactivating the back-up link to an inactive status is initiated by the IR.

12. A method as claimed in claim 9, wherein the step of detecting the network recovery comprises steps of:

detecting a recovery of communications between the IR and the primary ABR;

monitoring a link between the IR and the primary ABR for a predetermined period, to detect loss of communications; and

declaring a link recovery if loss of communications between the IR and the primary ABR is not detected within the predetermined period.

13. A method as claimed in claim 9, wherein the step of demoting the back-up link comprises a step of terminating an adjacency relationship between the IR and the alternate ABR.

15. A router as claimed in claim 14, wherein the back-up link is provisioned with a back-up interface type attribute.

16. A router as claimed in claim 15, wherein the means for maintaining the back-up link in a dormant state comprises means responsive to the assigned backup interface type attribute for controlling the router such that:

information respecting the back-up link is not advertised to adjacent routers; and

the back-up link is not identified as a valid route in a respective forwarding table of the router.

17. A router as claimed in claim 14, wherein the means for activating the back-up link comprises:

means for detecting the network failure affecting communications with the primary adjacent router;

means for promoting the back-up link to an active status; and

means for advertising the back-up link as a valid route.

18. A router as claimed in claim 17, wherein the means for detecting the network failure comprises:

means for detecting a loss of communications with the primary adjacent router;

means for monitoring a link to the primary adjacent router for a predetermined period, to detect recovery of communications; and

means for declaring a link failure if recovery of communications with the primary adjacent router is not detected within the predetermined period.

19. A router as claimed in claim 17, wherein the means for promoting the back-up link comprises means for negotiating an adjacency relationship with the alternate router.

20. A router as claimed in claim 14, further comprising means for deactivating the back-up link in response to a network recovery affecting communications with the primary adjacent router, such that traffic flow with the alternate router through the back-up link is terminated.

21. A router as claimed in claim 20, wherein the means for deactivating the back-up link comprises:

means for detecting the network recovery; and

means for demoting the back-up link to an inactive status.

22. A router as claimed in claim 21, wherein the means for detecting the network recovery comprises:

means for detecting a recovery of communications with the primary adjacent router;

means for monitoring a link to the primary adjacent router for a predetermined period, to detect loss of communications; and

means for declaring a link recovery if loss of communications with the primary adjacent router is not detected within the predetermined period.

23. A router as claimed in claim 21, wherein the means for demoting the back-up link comprises means for terminating an adjacency relationship with the alternate adjacent router.

25. A software program as claimed in claim 24, wherein the back-up link is provisioned with a back-up interface type attribute.

26. A software program as claimed in claim 25, wherein the software adapted to control the router to maintain the back-up link in a dormant state comprises software responsive to the assigned backup interface type attribute for controlling the router such that:

information respecting the back-up link is not advertised to adjacent routers; and

the back-up link is not identified as a valid route in a respective forwarding table of the router.

27. A software program as claimed in claim 24, wherein the software adapted to control the router to activate the back-up link comprises:

software adapted to control the router to detect the network failure affecting communications with the primary adjacent router;

software adapted to control the router to promote the back-up link to an active status; and

software adapted to control the router to advertise the back-up link as a valid route.

28. A software program as claimed in claim 27, wherein the software adapted to control the router to detect the network failure comprises:

software adapted to control the router to detect a loss of communications with the primary adjacent router;

software adapted to control the router to monitor a link to the primary adjacent router for a predetermined period, to detect recovery of communications; and

software adapted to control the router to declare a link failure if recovery of communications with the primary adjacent router is not detected within the predetermined period.

29. A software program as claimed in claim 27, wherein the software adapted to control the router to promote the back-up link comprises:

software adapted to control the router to negotiate an adjacency relationship with the alternate router; and

software adapted to control the router to update a respective forwarding table of the router to identify the back-up link as a valid route.

30. A software program as claimed in claim 24, further comprising software adapted to control the router to deactivate the back-up link in response to a network recovery affecting communications with the primary adjacent router, such that traffic flow with the alternate router through the back-up link is terminated.

31. A software program as claimed in claim 30, wherein the software adapted to control the router to deactivate the back-up link comprises:

software adapted to control the router to detect the network recovery; and

software adapted to control the router to demote the back-up link to an inactive status.

32. A software program as claimed in claim 31, wherein the software adapted to control the router to detect the network recovery comprises:

software adapted to control the router to detect a recovery of communications with the primary adjacent router;

software adapted to control the router to monitor a link to the primary adjacent router for a predetermined period, to detect loss of communications; and

software adapted to control the router to declare a link recovery if loss of communications with the primary adjacent router is not detected within the predetermined period.

33. A software program as claimed in claim 31, wherein the software adapted to control the router to demote the back-up link comprises:

software adapted to control the router to terminate an adjacency relationship with the alternate adjacent router; and

software adapted to control the router to update a respective forwarding table of the router to reflect an inactive status the back-up link.

14. A router adapted for protecting an Open Shortest Path First (OSPF) network against network failures affecting communications with a predetermined adjacent router using a back-up link to a predetermined alternate router, the router comprising:

means for maintaining the back-up link in a dormant state during normal operations of the network, such that no traffic is forwarded to the back-up link during normal operations of the network; and

means for activating the back-up link in response to a network failure affecting communications with the primary router, such that traffic can be routed through the back-up link.

24. A software program adapted to control a router of an Open Shortest Path First (OSPF) network to protect against network failures affecting communications with a predetermined primary adjacent router using a back-up link to a predetermined alternate router, the software program comprising:

software adapted to control the router to maintain the back-up link in a dormant state during normal operations of the network, such that no traffic is forwarded to the back-up link during normal operations of the network; and

software adapted to control the router to activate the back-up link in response to a network failure affecting communications with the primary router, such that traffic can be routed through the backup link.