consistent policy != consistent announcements
jyy at ans.net
Fri Mar 14 21:53:34 UTC 1997
Excuse me for responding myself here. Just like to clarify my previous
message a bit.
The note below does not intend to solve Randy's problem for his chosen
policy. It rather intends to describe a different policy used by many
ISPs which won't run into the same problem.
IMO, ISPs who are engaging in the 'hot potato' routing practice have the
obligation to announce consistent routes to its peers at different peering
points. It may require an ISP to change it's internal policy to achive
this with reasonable maintance work (like the one described below) or to
excercise whatever internal policy it decide but do more work (configuration
management,etc) to fulfill the obligation.
speaking for myself.
Date: Fri, 14 Mar 1997 12:48:49 EST
To: jgs at ieng.com
cc: vaf at valinor.barrnet.net, Sean Donelan <SEAN at sdg.dra.com>, nanog at merit.
From: Jessica Yu <jyy at ans.net>
Subject: Re: consistent policy != consistent announcements
Return-Path: owner-nanog at merit.edu
Sender: owner-nanog at merit.edu
If a provider/AS does not have the policy of dumping hot potatos to other
peers for the traffic to its customers who happen to multihome to those peers.
Then there is a simple way to do it. They can have policy of always favor
its own customer routes over the routes learned from other peers. This will
avoid the inconsistent announcement by eliminating the cases that some part
of the AS favors routes M from it's customer and other part favors M from
another peer, thus announce consistent routes to other peers.
It's very easy to manage this policy. Just assign lower (less favored)
local_pref to routes learned from peers than those learned from customers.
It's AS based. By using the default local_pref value, one only need to
assign a lower than default local_pref value to the peer AS at border routers.
A good side effect of this policy is that your customers routes will be
protected from being blackingholed from careless ISPs leaking/advertising your
customers routes but have no way to reach them.
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