Reference Guide

210 | Border Gateway Protocol IPv4 (BGPv4)
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Enable 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.
The default role for BGP on 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 FIB and CAM entries on the stack unit and continue forwarding traffic while the stack standby
unit 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 stack standby online as the master unit 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.
Enable graceful restart using the
configure router bgp graceful-restart command. The table below shows
the command and its available options:
Note: By default, BGP graceful restart is disabled.
Command Syntax Command Mode Usage
bgp graceful-restart
CONFIG-ROUTER-
BGP
Enable graceful restart for the BGP node.
bgp graceful-restart [restart-time
time-in-seconds]
CONFIG-ROUTER-
BGP
Set maximum restart time for all peers. Default is
120 seconds.
bgp graceful-restart [stale-path-time
time-in-seconds]
CONFIG-ROUTER-
BGP
Set maximum time to retain the restarting peer’s stale
paths. Default is 360 seconds.
bgp graceful-restart [role
receiver-only
]
CONFIG-ROUTER-
BGP
Local router supports graceful restart as a receiver
only.