Dell PowerConnect B-RX Configuration Manual page 922

26
Displaying BGP4 information
significantly and limit the availability of network resources. BGP graceful restart dampens the
network topology changes and limits route flapping by allowing routes to remain available between
routers during a restart. BGP Graceful restart operates between a router and its peers and must be
configured on both the router and its peers.
A BGP router with graceful restart enabled advertises its graceful restart capability and restart
timer to establish peering relationships with other routers. Once the restarting router is restarted, it
begins to reestablish BGP connections and receive routing updates from its peers. When the
restarting router receives all end-of-RIB markers from its helper neighbors, all of the routes are
recomputed, and newly computed routes replace the stale routes in the routing table. An
end-of-RIB marker indicates that it has received all of the BGP route updates.
During the restarting process, the helper neighbors will continue to use all of the routes learned
from the restarting router and mark them as stale for the length of the learned restart timer. If the
restarting router doesn't come back up within the restart timer, the routes marked stale will be
removed.
Configuring BGP graceful restart
To configure BGP Graceful Restart, you must enable it on all BGP peers where you want it to
operate and set the following timers:
•
•
NOTE
After configuring BGP Graceful Restart, you need to reset neighbor session whether or not the
neighbor session is up to enable BGP graceful restart. Use the clear ip bgp neighbor command to
clear and re-establish neighbor sessions.
Configuring BGP graceful restart on a router
Use the following command to enable the BGP graceful restart feature on a BigIron RX Switch.
BigIron RX(config)#router bgp
BigIron RX(config-bgp)#graceful-restart
Configuring BGP graceful restart timer
Use the following command to specify the maximum amount of time a router will maintain routes
from a restarting router and forward traffic to a restarting router.
BigIron RX(config)#router bgp
BigIron RX(config-bgp)#graceful-restart
BigIron RX(config-bgp)#graceful-restart restart-time 60
Syntax: graceful-restart restart-time <seconds>
The <seconds> variable sets the maximum number of seconds the restarting router will take to
restart. Also, the peer routers waits this number of seconds to re-establish BGP connection and to
keep using the learned routes from the restarting router. Enter 10 – 3600 seconds. The default
value is 120 seconds.
Configuring BGP graceful restart stale routes timer
Use the following command to specify the maximum amount of time a helper router will wait for an
end-of-RIB message from a restarting router before deleting stale routes learned from that
restarting router.
850
Restart Timer
Stale Routes Timer
BigIron RX Series Configuration Guide
53-1001810-01