102 Chapter 4: Intradomain IP Control Plane: Restarting OSPF Gracefully
Scenario 3: R1 Is Restart Signaling- and NSF-Capable, but R4 Is
Restart Signaling- and NSF-Incapable
In this case, OSPF restart in either R1 or R4 does not reduce the negative effects on other
routers. So to achieve any meaningful benefit from an OSPF restart signaling-capable router, its
neighbors must at least be capable of supporting the OSPF restart signaling mechanism.
Scenario 4: R1 Is Restart Signaling- and NSF-Capable, and R5 Is
Graceful Restart- and NSF-Capable
The OSPF restart signaling and graceful restart mechanisms are not interoperable. Therefore,
this configuration reduces to the previous scenario. That is, OSPF restart in either R1 or R5
would not lessen the negative effects on other routers. In other words, for deriving any benefit
from an OSPF restart signaling- or graceful restart-capable router, its neighbor must at least be
able to support the same OSPF restart mechanism.
Summary
This chapter described the undesirable effects OSPF restart can have on IP control and
forwarding planes. Two approaches that address these problems were described: OSPF restart
signaling and OSPF graceful restart. The operation of each approach was illustrated through
examples. A comparative analysis of the two approaches was presented. In addition, several
practical deployment scenarios for OSPF restart mechanisms were described.
References
1
RFC 2328, “OSPF Version 2,” J. Moy, April 1998.
2
Moy, J., OSPF Anatomy of an Internet Routing Protocol. Boston: Addison-Wesley, 1998.
3
Zinin, A., A. Roy, and L. Nguyen, “OSPF Restart Signaling,” Internet Draft, Work in progress.
4
Friedman, B., et al., “OSPF Link-Local Signaling,” Internet Draft, Work in progress.
5
Nguyen, L., A. Roy, and A. Zinin, “OSPF Out-of-Band LSDB Resynchronization,” Internet
Draft, Work in progress.
6
RFC 3623, “Graceful OSPF Restart,” J. Moy, P. Pillay-Esnault, and A. Lindem, November
2003.
This page intentionally left blank

Get Fault-Tolerant IP and MPLS Networks now with the O’Reilly learning platform.

O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.