[c-nsp] [Query] Bgp Session timers

[Christoph Loibl]

Hi!

On Jun 1, 2007, at 12:21 AM, Simon Leinen wrote:

> Arie Vayner \(avayner\) writes:
>> Danny,
>> With iBGP the timers for BGP are not really important... You
>> actually need to worry about the IGP convergence.
>> The reason for that is that usually when a link fails, you don't
>> really expect the BGP session to the RR to go down, but just use the
>> redundant IGP path.
>
> Yes, but what about when a router fails, in particular a border
> (eBGP+iBGP) router?
>
> In such a case, iBGP timers (or the configuration of a mechanism such
> as BFD) will determine how long it takes for other routers that the
> eBGP routes from the dead router have to be dropped.  This can be very
> important, because using the dead router's eBGP routes can mean
> blackholing traffic.

No need to adjust the iBGP timers in that case. Your bgp-next-hop  
(which is ideally a loopback-ip of the crashed router) will simply  
disapear from your internal routing-table, and all iBGP neighbors  
(also the RRs) will remove all routes that are unreachable (because  
of the unreachable next-hop) from their tables. You only rely on the  
convergence-time of your igp (ospf? isis? ...?) to remove the "dead"  
loopback-ip from its table and the calculation of BGP that is  
triggered when the loopback-ip disappears.

Stoffi

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