Netgear XCM8806 Chassis User Manual - Page 676

NETGEAR 8800 User Manual Normally, support for opaque LSAs is autonegotiated between OSPF neighbors. In the event that you experience interoperability problems, you can disable opaque LSAs across the entire system using the following command: disable ospf capability opaque-lsa To re-enable opaque LSAs across the entire system, use the following command: enable ospf capability opaque-lsa If your network uses opaque LSAs, NETGEAR recommends that all routers on your OSPF network support opaque LSAs. Routers that do not support opaque LSAs do not store or flood them. At minimum a well interconnected subsection of your OSPF network must support opaque LSAs to maintain reliability of their transmission. Graceful OSPF Restart RFC 3623 describes a way for OSPF control functions to restart without disrupting traffic forwarding. Without graceful restart, adjacent routers will assume that information previously received from the restarting router is stale and will not be used to forward traffic to that router. However, in many cases, two conditions exist that allow the router restarting OSPF to continue to forward traffic correctly. The first condition is that forwarding can continue while the control function is restarted. Most modern router system designs separate the forwarding function from the control function so that traffic can still be forwarded independent of the state of the OSPF function. Routes learned through OSPF remain in the routing table and packets continue to be forwarded. The second condition required for graceful restart is that the network remain stable during the restart period. If the network topology is not changing, the current routing table remains correct. Often, networks can remain stable during the time for restarting OSPF. Restarting and Helper Mode Routers involved with graceful restart fill one of two roles: the restarting router or the helper router. With graceful restart, the router that is restarting sends out Grace-LSAs informing its neighbors that it is in graceful restart mode, how long the helper router should assist with the restart (the grace period), and why the restart occurred. If the neighboring routers are configured to help with the graceful restart (helper-mode), they will continue to advertise the restarting router as if it was fully adjacent. Traffic continues to be routed as though the restarting router is fully functional. If the network topology changes, the helper routers will stop advertising the restarting router. The helper router will continue in helper mode until the restarting router indicates successful termination of graceful restart, the Grace-LSAs expire, or the network topology changes. A router can be configured for graceful restart, and for helper-mode separately. A router can be a helper when its neighbor restarts, and can in turn be helped by a neighbor if it restarts. Planned and Unplanned Restarts Two types of graceful restarts are defined: planned and unplanned. A planned restart would occur if the software module for OSPF was upgraded, or if the router operator decided to restart the OSPF control function for some reason. The router has advance warning, and is 676 | Chapter 24. OSPF