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I am trying to determine exactly why GR timers are recommended to be less than HOLDTIME timers Per RFC4724:

A suggested default for the Restart Time is a value less than or equal to the HOLDTIME carried in the OPEN.

and

When the Receiving Speaker detects termination of the TCP session for a BGP session with a peer that has advertised the Graceful Restart Capability, it MUST retain the routes received from the peer for all the address families that were previously received in the Graceful Restart Capability and MUST mark them as stale routing information.

It seems that GR being longer than HOLDTIME (ex: GR = 20s, HOLDTIME = 10s) would mean, even if HOLDTIME expires, the routes previously marked stale would still be retained in FIB by the receiving speaker, and the behavior of GR would be the same. Is this accurate?

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That specific recommendation does not make any sense to be honest.

The GR timer is started by the GR-helper node upon BGP HOLDTIME expiry, assuming no other factors cause the BGP session to be terminated (eg link down event for eBGP, BFD down etc).

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