Users Guide

Enabling Graceful Restart
To lessen the negative eects of a BGP restart, use the graceful restart feature.
Dell Networking OS advertises support for this feature to BGP neighbors through a capability advertisement. You can enable
graceful restart by router and/or by peer or peer group.
NOTE: By default, BGP graceful restart is disabled.
The default role for BGP is as a receiving or restarting peer. If you enable BGP, when a peer that supports graceful restart resumes
operating, Dell Networking OS performs the following tasks:
• Continues saving routes received from the peer if the peer advertised it had graceful restart capability. Continues forwarding
trac to the peer.
• Flags routes from the peer as Stale and sets a timer to delete them if the peer does not perform a graceful restart.
• Deletes all routes from the peer if forwarding state information is not saved.
• Speeds convergence by advertising a special update packet known as an end-of-RIB marker. This marker indicates that the peer
has been updated with all routes in the local RIB.
If you congure your system to do so, Dell Networking OS can perform the following actions during a hot failover:
• Save all forwarding information base (FIB) and content addressable memory (CAM) entries on the line card and continue
forwarding trac while the secondary route processor module (RPM) is coming online.
• Advertise to all BGP neighbors and peer-groups that the forwarding state of all routes has been saved. This prompts all peers to
continue saving the routes they receive and to continue forwarding trac.
• Bring the secondary RPM online as the primary and re-open sessions with all peers operating in No Shutdown mode.
• Defer best path selection for a certain amount of time. This helps optimize path selection and results in fewer updates being sent
out.
To enable graceful restart, use the configure router bgp graceful-restart command.
• Enable graceful restart for the BGP node.
CONFIG-ROUTER-BGP mode
bgp graceful-restart
• Set a maximum restart time for all peers.
CONFIG-ROUTER-BGP mode
bgp graceful-restart [restart-time time-in-seconds]
The default is 120 seconds.
• Set maximum time to retain the restarting peer’s stale paths.
CONFIG-ROUTER-BGP mode
bgp graceful-restart [stale-path-time time-in-seconds]
The default is 360 seconds.
• Local router supports graceful restart as a receiver only.
CONFIG-ROUTER-BGP mode
bgp graceful-restart [role receiver-only]
Enabling Neighbor Graceful Restart
BGP graceful restart is active only when the neighbor becomes established. Otherwise, it is disabled.
Graceful-restart applies to all neighbors with established adjacency.
192
Border Gateway Protocol IPv4 (BGPv4)