Symmetrical Routing with a single router and two providers.....

Photon - NOL Staff <photon@nolsun1.nol.net> Tue, 27 June 1995 01:51 UTC

Message-Id: <199506270136.AA10319@interlock.ans.net>
Date: Mon, 26 Jun 1995 20:38:51 -0500 (CDT)
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From: Photon - NOL Staff <photon@nolsun1.nol.net>
To: bgp@ans.net
Subject: Symmetrical Routing with a single router and two providers.....
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Please excuse my ignorance while you read on.....


I've been keeping up as best as I can with BGP4, but I have obviously missed
a few concepts here and there.  I see how the DPA helps in all of the listed
configurations in draft-ietf-dpa-01.txt, but could someone explain to me how
and if it could help this situation (which I face in about 3 weeks when our new
router comes in):

                             AS4
                            /  \
                           /    \
                          / (NAP)\
                        AS1------AS2
                          \      /
                           \    /
                            \  /
                             AS3


In this diagram, AS3 is the end customer, and has a linkup to both AS1 and
AS2.  AS1 and AS2 are both major "backbone" AS's with anywhere from 8-20k of
customer routes.  Both of the (T1) links are coming from the same physical
router in AS3, and AS3 has one flat, simple route internally, on one local
ethernet.  Therefore AS3 has no need, desire or ability to split internally as
far as routing is concerned.  AS3 would like to (optimally, but seeming 
impossible) use the best/fastest path for each connection based on intelligent
metrics, and not lose routing symmetry.  While both AS1 and AS2 will be used
in a load balanced situation for AS3's normal traffic, AS3 also wants a BGP
setup that will allow all traffic to go through one of its providers, should
the other provider go down temporarily.  Since the two providers going down
simultaneously is a rare occurance, this should provide for high availability.

What kind of BGP setup could offer a decent method of good load balancing
between AS1 and AS2 for customer AS3?

Would this be a situation in which AS3 would benenfit from taking on full
routing, or would AS3 be better off taking the customer routes of AS1 and
AS2, and using DPA and weighted default routes to acheive symmetry?


Silently Going Insane,

	Brandon
	photon@nol.net

Symmetrical Routing with a single router and two … Photon - NOL Staff
Re: Symmetrical Routing with a single router and … Enke Chen