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Dell EMC Configuration Guide for the S4048T–ON System 9.14.2.4

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Enabling Graceful Restart

Use this feature to lessen the negative effects of a BGP restart.

Dell EMC 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 EMC 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 EMC 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 following command.

bgp graceful-restart [restart-time seconds] [stale-path-time seconds] [role receiver-only]

To return to the default, use the no bgp graceful-restart command.

  • Enable graceful restart for the BGP node.
    CONFIG-ROUTER-BGP mode
    bgp graceful-restart
  • Set maximum restart time, in seconds, to restart and bring-up all the peers.
    CONFIG-ROUTER-BGP mode
    bgp graceful-restart [restart-time time-in-seconds]
    The default is 120 seconds.
  • Set maximum time, in seconds, 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.
  • Enable the local router to support graceful restart as a receiver only.
    CONFIG-ROUTER-BGP mode
    bgp graceful-restart [role receiver-only]

Example configuration for enabling graceful restart

The below example configuration shows how to enable the BGP graceful restart.

DellEMC# configure terminal
DellEMC(conf)# router bgp 400
DellEMC(conf-router_bgp)# bgp graceful-restart
DellEMC(conf-router_bgp)# exit

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