[c-nsp] behavior of BGP when new address families are enabled (BGP dynamic capability)

[Jason Lixfeld]

I went through this a few months back.

XR has had something called multi-instance BGP since 4.2. I'm not sure if it's enabled by default or in conjunction with nsr and/or graceful-restart.  It seems to works just like multi-session BGP in IOS, but it's not the same.  The two do not interoperate.  If one enables multi-session in IOS and multi-instance in XR, the session will never establish.  It won't even try to fall back to single session.

With multi-instance, you can add AFs with no adverse effects to existing sessions in any other AF.

On 2013-08-08, at 10:14 AM, Adam Vitkovsky <adam.vitkovsky at swan.sk> wrote:

> There's a 'suppress capability' knob in XR, but unfortunately only for
> 4-byte-asn. 
> You can try 'transport multi-session' in IOS, but I can't find it in XR. 
> 
> adam
> -----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of
> Tassos Chatzithomaoglou
> Sent: Thursday, August 08, 2013 3:07 PM
> To: Nick Hilliard
> Cc: cisco-nsp
> Subject: Re: [c-nsp] behavior of BGP when new address families are enabled
> (BGP dynamic capability)
> 
> Nick, that's what also i'm doing in case of dual RRs. But, as you say, it's
> pain in the a**.
> I was hoping for at least a simple knob like "activate-on-reset" which would
> enable this and similar capabilities only after the BGP session was reset
> (for whatever reason).
> Then i could pre-configure all sessions with the new address families and
> just do a bgp reset on the RRs to activate them.
> 
> Nick Hilliard wrote on 08/08/2013 15:49:
>> On 08/08/2013 13:36, Tassos Chatzithomaoglou wrote:
>>> Can anyone provide any inside info what we should expect in this area?
>> broadly speaking, you need to plan on lots of bgp session resets.  As 
>> you note there is no option in the bgp protocol at the moment to 
>> renegotiate capabilities after session startup.  So each side would 
>> need to be aware of all future AFIs that you would want to run on each
> session.
>> 
>> In practice, I've been handling this recently having a preexisting 
>> configuration which uses multiple RRs for each client bgp speaker.  
>> This means that you can upgrade one RR to supporting the new afi / 
>> capability, then upgrade each session, one by one, then when 
>> everything is configured up on the migrated RR, you can shift the 
>> other side over.  This is very messy though.  It means that you need 
>> to disentangle the peer-group configurations for each RR session, and 
>> then reconfigure them once the work is done.  So while it can be done 
>> hitlessly (and in many cases scriptably) with some planning, it's still a
> pain.
>> 
>> Nick
>> 
>> 
>> 
> 
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