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

[Tassos Chatzithomaoglou]

Having a BGP session with multisession capability enabled between 7200s (SRE6), brought up automatically another BGP session when the new address family got configured.

BGP neighbor is x.x.x.x,  vrf TEST-VRF,  remote AS 65121, external link
  BGP version 4, remote router ID x.x.x.x
  Session state = Established, up for 30w3d
  Last read 00:00:39, last write 00:00:02, hold time is 180, keepalive interval is 60 seconds
  BGP multisession with 2 sessions (2 established), first up for 30w3d
  Neighbor sessions:
    2 active, is multisession capable
  Neighbor capabilities:
    Route refresh: advertised and received(new) on session 1, 2
    Four-octets ASN Capability: advertised and received on session 1, 2
    Address family IPv4 Unicast: advertised and received
    Address family IPv6 Unicast: advertised and received
    Multisession Capability: advertised and received
...
 For address family: VPNv4 Unicast
  Translates address family IPv4 Unicast for VRF TEST-VRF
  Session: x.x.x.x session 1
....
 For address family: VPNv6 Unicast
  Translates address family IPv6 Unicast for VRF TEST-VRF
  Session: x.x.x.x session 2


Interesting...but also a little bit confusing....

--
Tassos

Adam Vitkovsky wrote on 08/08/2013 17:14:
> 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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