[30688] in North American Network Operators' Group
Re: Community NO-EXPORT
daemon@ATHENA.MIT.EDU (Jeff Haas)
Thu Aug 24 11:19:24 2000
Date: Thu, 24 Aug 2000 11:17:34 -0400
From: Jeff Haas <jeffhaas@merit.edu>
To: Bradley Dunn <bradley@dunn.org>
Cc: nanog@merit.edu
Message-ID: <20000824111734.E17236@outtolunch.merit.edu>
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In-Reply-To: <20000823095559.A21106@kookreport.com>; from bradley@dunn.org on Wed, Aug 23, 2000 at 09:55:59AM -0700
Errors-To: owner-nanog-outgoing@merit.edu
On Wed, Aug 23, 2000 at 09:55:59AM -0700, Bradley Dunn wrote:
> On Wed, Aug 23, 2000 at 10:03:21AM -0400, Kai Schlichting wrote:
> > Correct me if I'm wrong, but isn't there a synchronization issue here
> > as well? E.g.: AS2 is transit provider, probably has bgp synchronization
> > on (default), and will only propagate routes to other AS's that have
> > made it into their IGP. The question then is: have all 3 routes made
> > it into AS2's IGP successfully? Only if the answer is yes, will it
> > actually propagate that /16.
>
> Synchronization is almost universally disabled in the real world.
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.
> None of the IGPs in use today would cope well with a full BGP
> table redistributed into them. Redistribution of BGP->IGP is
> rarely needed or advisable.
However, its a wonderful way to see the failure states of your router's
IGPs. :-)
--
Jeffrey Haas - Merit RSng project - jeffhaas@merit.edu
