Administrator Guide

Enabling Graceful Restart
Use this feature to lessen the negative effects of a BGP restart.
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
traffic 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 the peer
has been updated with all routes in the local RIB.
If you configure 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 traffic 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 traffic.
● 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 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.
With the graceful restart feature, Dell Networking OS enables the receiving/restarting mode by default. In Receiver-Only mode,
graceful restart saves the advertised routes of peers that support this capability when they restart. This option provides support
for remote peers for their graceful restart without supporting the feature itself.
You can implement BGP graceful restart either by neighbor or by BGP peer-group. For more information, refer to the Dell
Networking OS Command Line Interface Reference Guide.
● Add graceful restart to a BGP neighbor or peer-group.
CONFIG-ROUTER-BGP mode
neighbor {ip-address | peer-group-name} graceful-restart
● Set the maximum restart time for the neighbor or peer-group.
Border Gateway Protocol IPv4 (BGPv4)
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