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

[Nick Hilliard]

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