[c-nsp] BGP fast converge

[Mario Velazquez]

Hi Oli

thanks a lot for your advice, the reason for the eBGP configuration is a 
customer requirement (i have already tried to make him change the 
config, but no luck) y have a 7600/SUP720 as a N-PE and a 3750ME 
(12.2(25).SEG) as U-PE y was looking in the feature navigator and the 
3750 doesn't support  any of the BGP features,
is there any other option? or do you think a topology change would be 
the best idea.

Thanks a lot

Mario

Oliver Boehmer (oboehmer) wrote:
> Mario Velazquez <> wrote on Friday, July 28, 2006 3:27 PM:
>
>   
>> Hi, i am having some problems in my metro network, bgp convergence is
>> really a problem, i was looking arround for some fast convergence
>> features like BGP Fast Peering Session Deactivation and BGP Next-Hop
>> Address Tracking. this is what i have so far:
>>
>>
>> CE1 and CE3 are in the same site, the same for CE2 and CE4, the CE-PE
>> connection is bgp.
>> All CE are running ospf with more or less than 6000 routes each.
>> the problem is between CE1/PE1 and CE3/PE3 because when if one port
>> fails in SW1/SW2 the bgp session will not be dropped until the dead
>> timer expires (180s).
>>
>> i have this configuration in all CE
>>
>> outer bgp 222
>> no synchronization
>> bgp log-neighbor-changes
>> network 20.0.0.0
>> neighbor 1.1.1.1 remote-as 13591
>> neighbor 1.1.1.1 ebgp-multihop 3
>> neighbor 1.1.1.1 fall-over
>> neighbor 3.3.3.3 remote-as 13591
>> neighbor 3.3.3.3 ebgp-multihop 3
>> neighbor 3.3.3.3 fall-over
>> no auto-summary
>>
>> But nothing seems to change, in the case of a port fail in SW1 or SW2
>> bgp stills wait for the peer dead timer.Is there something missing? or
>> am i using the wrong feature? or i have a bad config
>>     
>
> Is there a specific reason why you enabled ebgp multihop between CE and
> PE? Because if you used a direct peering using the link address(es), a
> link-down of the CE interface would trigger session-down without any
> configuration.
>
> But regarding "fall-over": This mechanism relies on the neighbor
> disappering from your RIB (i.e. no more routes towards the neighbor). If
> you connect to the PE using a switch and the remote switch port dies,
> you will still have the route towards this neighbor in your RIB (as your
> side of the link is still up), so FSD will never fire.
>
> To cover these failures in a scalable manner, you need the interaction
> between BFD and BGP, but this is brand new and only available in some
> releases (BFD for BGP, "neighbor fall-over bfd"). Then BFD will track
> your neighbor reachability, and signal BGP when it goes away. 
>
> For the time being: Why not just decrease the hello timer? You do want
> to check with your peer as tuning it too low is not really polite as
> this doesn't scale..
>
> 	oli
>
>