[107646] in North American Network Operators' Group
RE: why not AS number based prefixes aggregation
daemon@ATHENA.MIT.EDU (Paul Francis)
Tue Sep 9 14:03:07 2008
Date: Tue, 9 Sep 2008 14:02:57 -0400
In-Reply-To: <48C5DDA4.30307@vaxination.ca>
From: Paul Francis <francis@cs.cornell.edu>
To: =?iso-8859-1?Q?Jean-Fran=E7ois_Mezei?= <jfmezei@vaxination.ca>,
<nanog@nanog.org>
Errors-To: nanog-bounces@nanog.org
Sorry, my question was not clear. By "entries" I meant "routes" or
"prefixes". For instance, some ISPs today deaggregate in order to
load-balance, so they advertise multiple prefixes or routes instead of =
one.
Of course, the "right" number would vary from ISP to ISP (as someone =
already
pointed out to me), but I'm not even sure what the criteria would be for =
how
many routes one needs to load balance...i.e. depends on the number of AS
neighbors?, depends on the number of depends on the number of BGP =
neighbors?,
depends on your load balancing mechanism (MEDs versus path prepending =
versus
....???)?
The point is this...BGP seems to give use two tools...a machete (AS =
numbers)
and a scalpel (prefixes). If I want to cut a steak (load balance), the
machete is too coarse, the scalpel is too fine. What's the right =
tool???
PF
> -----Original Message-----
> From: Jean-Fran=E7ois Mezei [mailto:jfmezei@vaxination.ca]
> Sent: Monday, September 08, 2008 10:21 PM
> To: nanog@nanog.org
> Subject: Re: why not AS number based prefixes aggregation
>=20
> Paul Francis wrote:
>=20
> > AS, or even dozens. So I'm curious...if we could wave a magic wand
> and
> > control the exact number of entries any AS needs to advertise, what
> would
> > folks consider to be roughly the right number of entries?
>=20
> Wouldn't this greatly depend on the span/breath of your network ? If
> you
> are a large nationwide (or even international) ISP/network, then you
> want to be able to distribute your network so that someone on west
> coast
> trying to reach one of your west coast IP addresses will have a pretty
> direct route into your west coast infrastructure instead of funnelling
> all traffic into one central location.
>=20
> But a smaller ISP based in only one city would not need to distribute
> traffic through different entry points since traffic from each transit
> provider would end up on the same router.
>=20
> So I am not sure one could draw any "right number of entries".
>=20
>=20
