[c-nsp] bgp keepalive/hold timers on ethernet links

[Bruce Pinsky]

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Simon Leinen wrote:
> matthew zeier writes:
> 
>>BGP's default 60/180 timers are too long
> 
> 
> Note that 60/180 is *Cisco's* default for BGP.  RFC 1771 (BGP-4)
> suggests 30/90.  This is still long, but already way better for your
> situation.
> 
> 
>>to go before dropping the peer.  The PHB wanted 1 second keepalives
>>and a 3 second hold timer.  However, as soon as I started pulling in
>>traffic (and only 50Mbps), I began frequently dropping the the peer.
> 
> 
> Interesting.  Maybe BGP is sometimes busy for >2 seconds
> sending/receiving or processing BGP updates (from other peers?), so
> that the hold timer expires.
> 
> We use 10/30 on some important peerings, in particular all iBGP
> peerings.  That seems to work nicely for us so far (note that we don't
> take full routes; we only have about 30'000 IPv4 BGP routes).
> 
> 
>>I'm guessing that these timers are too aggressive - anyone have any
>>practical suggestions on how to fix this?
> 
> 
> The obvious one is: use a longer hold time.  The other was mentioned
> too: try BFD when BGP support comes out on your platform (same as
> ours).  I would be curious how well this works.  I'd assume that BFD
> will be handled on the MSFC at least for the time being, so it would
> still compete with other processing there.  Hopefully BFD will at
> least be handled in an interrupt handler.


Still another option, if the routers are loopback peered instead of
interface peered, would be to leave the BGP timers alone and instead
utilize BGP Next Hop Tracking to cause quick withdrawl of the routes when
the IGP detects that the loopback interface is no longer reachable.  Then
it would not matter how long it took the actual BGP session to come down.

Alas, as with BFD, the feature has yet to find its way into a release for
the 6500/7600, but is available for platforms that are supported by 12.0S
and 12.3T.

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bep

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