[j-nsp] Sending iBGP prefixes to another iBGP neighbour

[Justin Seabrook-Rocha]

On May 5, 2016, at 09:37, Mike Williams <mike.williams at comodo.com> wrote:
> 
> Hey all,
> 
> I could very well either be doing this completely wrong, or attempting to do 
> the impossible, but...
> 
> We have BIRD on Linux using BGP to send prefixes to the MX104 over a direct 
> connection, I need to send those prefixes to an MX80 directly connected to the 
> 104.
> 
> At the 104 end of the 104<->80 peering there is just an export policy, that 
> simply matches on "from protocol bgp" and the BGP community assigned the 
> prefixes I want, then accept and next-hop self.
> 
> In isolation, the policy works.
> 
>> test policy blah <prefix>/32
> ...
> ...
> 
> Policy blah: 1 prefix accepted, 0 prefix rejected
> 
> 
> The MX104 never actually advertises any prefixes to the MX80 though.
> 
>> show route advertising-protocol bgp <mx80>
> ... zilch ...
> 
> 
> Is there some inbuilt protection preventing iBGP prefixes from being sent to 
> another iBGP neighbour?
> Or am I just doing it wrong?
> 
> advertise-peer-as and as-override have no impact.
> 
> 
> Thanks
> 
> -- 
> Mike Williams
> _______________________________________________
> juniper-nsp mailing list juniper-nsp at puck.nether.net
> https://puck.nether.net/mailman/listinfo/juniper-nsp

Yes, BGP will refuse to readvertise iBGP learned routes to other iBGP neighbors. This is part of the basic loop prevention mechanisms of BGP. I don’t think it can be disabled.

There are really only three solutions to your problem. A full mesh of iBGP neighbor relationships, route reflection, or BGP confederation. You probably just want to set up an iBGP session between BIRD and the MX80. Or you could configure the MX104 as a route reflector.

Justin Seabrook-Rocha
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