[30689] in North American Network Operators' Group
Re: Community NO-EXPORT
daemon@ATHENA.MIT.EDU (Danny McPherson)
Thu Aug 24 11:50:26 2000
Message-Id: <200008242155.PAA11938@tcb.net>
To: nanog@merit.edu
From: Danny McPherson <danny@tcb.net>
Reply-To: danny@tcb.net
Date: Thu, 24 Aug 2000 15:55:12 -0600
Errors-To: owner-nanog-outgoing@merit.edu
No, BGP synchronization does indeed refer to the
requirement that the destination network be available
via the IGP.
If it were just the BGP NEXT_HOP value it wouldn't be
of much use, as intermediate nodes perform forwarding
based on the DA in the packet and [if not synchronized]
won't find a match. As a result, the packet will be
discarded.
Of course, most folks simply have full mesh IBGP
(perhaps via RR or confeds) and so there's no reason
too enable [or not disable] BGP synchronization.
-danny
> Color me confused, but isn't the synchronization waiting on the
> NEXT_HOPs showing up in your IGP, not the actual BGP route?
>
> After all, the issue is this:
>
> BR-A - (your internal network) - BR-B
>
> A route shows up at BR-A with a nexthop of some interface on BR-A
> (or the loopback interface of BR-A). It is then propogated via
> iBGP to BR-B.
>
> It is only unsafe to install said route and propogate it BR-B's peers
> if the route's nexthop is not reachable by BR-B.
>
> This is a far cry from having to inject your BGP into your IGP.
>
> I will note that this isn't how Cisco has it documented, and I don't know
> how they actually treat the sync issue. The documentation actually
> says it does wait for the route to show up in the IGP.
