[144194] in North American Network Operators' Group
Preferring peers over customers [was: Do Not Complicate Routing
daemon@ATHENA.MIT.EDU (Patrick W. Gilmore)
Sun Sep 4 21:19:12 2011
In-Reply-To: <m2mxekyt05.wl%randy@psg.com>
From: "Patrick W. Gilmore" <patrick@ianai.net>
Date: Mon, 5 Sep 2011 09:18:33 +0800
To: North American Operators' Group <nanog@nanog.org>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Sep 5, 2011, at 4:03, Randy Bush <randy@psg.com> wrote:
>> Because routing to peers as a policy instead of customer as a matter
>> of policy, outside of corner cases make logical sence.
>=20
> welcome to the internet, it does not always make logical sense at first
> glance.
>=20
> the myth in academia that customers are always preferred over peers
> comes from about '96 when vaf complained to asp and me (and we moved it
> to nanog for general discussion) that we were not announcing an
> identical prefix list to him at east and west. the reason turned out to
> be that, on one of the routers, a peer path was shorter in some cases,
> so we had chosen it. we were perfectly happy with that but vaf was not,
> and he ran the larger network so won the discussion.
The "myth" comes from engineers at large networks saying it is so.
We could also have a small miscommunication here. For example, if a custome=
r were multi-homed to a peer, and the customer and peer were on the same rou=
ter, and the customer had prepended a single time (making the AS path equal)=
, by your original statement you would have sent traffic to the peer. Most p=
eople would find that silly. (And please do not point out customers and pee=
rs do not connect to the same router, this is a simple example for illustrat=
ive purposes.)
However, the statement you make above says that you preferred the peer becau=
se "the path was shorter". You do not specify if that is IGP distance, AS p=
ath length, or some other metric, but it implies if the path were equal, you=
would prefer the customer - especially since the customer was preferred on t=
he other coast. So there may be assumptions on one side or the other that a=
re not clear which are causing confusion.
Either way, this seems operationally relevant.
I would like the large networks of the world to state whether they prefer th=
eir customer routes over peer routes, and how. For instance, does $NETWORK p=
refer customers only when the AS path is the same, or all the time no matter=
what?
Let's leave out corner cases - e.g. If a customer asks you, via communities o=
r otherwise, to do something different. This is a poll of default, vanilla c=
onfigurations.
Please send them to me, or the list, with this subject line. I shall compil=
e the results and post them somewhere public. If you cannot speak for your c=
ompany, I will keep your name private.
Thanx.
--=20
TTFN
patrick
