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DES-7200 Configuration Guide Chapter 6 BGP
Configuration
6-30
Initially, the BGP protocol establishes the neighbor relationship and negotiates
respective GR capability with the GR Capability field of the OPEN message. At a
point, the device reboots and the BGP session is disconnected. The neighbor
detects disconnection. With GR supported, the BGP neighbor keeps the route of
the GR Restarter valid but identifies it Stale. The GR Restarter reboots and
reestablish connection with the GR Helper and waits the route update message
and EOR label from the GR Helper. After receiving the EOR label from all
neighbors, the BGP Restarter calculates routes and update the routing table, and
begins to send update routes to the GR Restarter. Upon the receipt of these
routes, the GR Helper removes the Stale tag from these routes. Then it deletes
the routes tagged with Stale after receiving the EOR label from the BGP Restarter,
calculates routes and updates the routing table.
Some key timers are defined to assist the implemetation of BGP GR:
Restart-Timer: The GR Restarter notifies the GR Helper of restart time that the
GR Helper needs to wait before reestablishing the BGP connection. You can
modify this value by the bgp graceful-restart restart-time command.
Wait-For-EOR Timer: Time the GR Restarter needs to wait for the EOR label of
all GR Helpers. After receiving the EOR label of all GR Helpers or the timer times
out, the GR Restarter calculates optimal routes and updates the routing table.