Netgear XCM8806 Chassis User Manual - Page 719

NETGEAR 8800 User Manual Note: When entering an AS number in a policy file, you must enter a unique 2-byte or 4-byte AS number. The transition AS number, AS 23456, is not supported in policy files. To delete a static BGP network, use the following command: configure bgp delete network {address-family [ipv4-unicast | ipv4-multicast]} [all | ] Graceful BGP Restart It is possible for BGP 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 won't be used to forward traffic to that router. However, in many cases, two conditions exist that allow the router restarting BGP 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 BGP function. Routes learned through BGP 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 BGP. With graceful BGP restart, routes received from a restarting router are marked as stale, but traffic continues to be forwarded over these routes during the restart process. Restarting and Receiver Mode Routers involved with graceful restart fill one of two roles: the restarting router or the receiving router. When a receiving router detects that the TCP connection with its peer is reset, it assumes that the peer has entered graceful restart. If the neighboring routers are configured to help with the graceful restart (receiver-mode), they will continue to advertise the restarting router as if it was fully functional. Traffic continues to be routed as though the restarting router is fully functional. The receiver router will continue in receiver mode until the restarting router re-establishes the TCP session, indicating successful termination of graceful restart, the restart timers expire. A router can be configured for graceful restart, and for receiver-mode separately. A router can be a receiver when its neighbor restarts, and can in turn be helped by a neighbor receiver-mode router if it restarts. Planned and Unplanned Restarts Two types of graceful restarts are defined: planned and unplanned. A planned restart occurs when the software module for BGP is upgraded, or if the router operator decides to restart the BGP control function for some reason. An unplanned restart occurs when there is some kind of system failure that causes a remote reboot or a crash of BGP, or when an MSM/MM failover occurs. You can decide to configure a router to enter graceful restart for only planned Chapter 26. BGP | 719