[153143] in North American Network Operators' Group
Re: HE.net BGP origin attribute rewriting
daemon@ATHENA.MIT.EDU (David Barak)
Thu May 31 07:56:44 2012
In-Reply-To: <4FC75565.4000404@foobar.org>
From: David Barak <thegameiam@yahoo.com>
Date: Thu, 31 May 2012 07:55:28 -0400
To: Nick Hilliard <nick@foobar.org>
Cc: "nanog@nanog.org" <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On May 31, 2012, at 7:26 AM, Nick Hilliard <nick@foobar.org> wrote:
> There are many useful ways to build a
> multi-exit discrimination policy. Using origin is not one of them, in my
> opinion.
>=20
> The problem is that origin is ranked one place higher than MED. So if you=
> don't rewrite it, you are automatically giving your upstreams an inherent
> means of strongly influencing the tie-breaking policy. If this were an
> attribute which actually meant something, then maybe there would be some
> point in paying attention to it, but it conveys no useful information thes=
e
> days. IOW, it is completely pointless these days and you almost certainly=
> want to work the possibility of any upstream tweaking it.
>=20
> Nick
>=20
I disagree. Origin is tremendously useful as a multi-AS weighting tool, and=
isn't the blunt hammer that AS_PATH is. The place where I've gotten the mo=
st benefit is large internal networks, where there may be multiple MPLS clou=
ds along with sites cascaded off of them - it provides a way of sending "sof=
t" preferences down the transitive chain. Also useful is "set origin egp XX=
" - on a route injector, that can post-pend an ASN and limit the spread of a=
route while still allowing the same transitive properties.
David Barak
Sent from a mobile device, please forgive autocorrection.
