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One could also presume that BFD should also be considered
dangerous, if enabled.

- - ferg


- -- Pascal Gloor <pascal.gloor@spale.com> wrote:

> Is it likely that BGP times out before underlying IP topology  
> reconvergences
> after a link/node failure? Do service providers ever set such low  
> values of
> BGP timeouts that BGP timeout will occur?
>
> If not, what else may cause a BGP session to time out?

Depending on your hardware, you can trigger your BGP and IGP to shut  
sessions when the peer is gone.

On some cisco, you can have BFD (Bidirectional Forwarding Detection).  
you have to enable this on both sides. If BFD notices the peer is  
down, it will notify OSPF,BGP,... (if configured so).

for example:

!
interface GigabitEthernet0/0
  ip address 10.1.1.1 255.255.255.252
  bfd neighbor 10.1.1.2
  bfd interval 250 min_rx 250 multiplier 3
  ip ospf bfd
!

This will send a BFD packet every 250ms, expect one every 250ms and  
if 3 packets are missed (after 750ms) it will tell OSPF to shut any  
session towards 10.1.1.2 (or routed via 10.1.1.2 for the BGP case).


Pascal

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--
"Fergie", a.k.a. Paul Ferguson
 Engineering Architecture for the Internet
 fergdawg(at)netzero.net
 ferg's tech blog: http://fergdawg.blogspot.com/



