BGP full-mesh

From: Bogdan Sass (bogdan.sass@catc.ro)
Date: Wed Jan 28 2009 - 07:23:45 ARST


    A student of mine asked me a question today. One of those questions
that seem simple, but when you think about them you realize you don't
really know the answer. So I decided to come here for some guidance :)

    The question was: "Why do we need a full-mesh between _all_ the
BGP-running routers in an AS?" (we're not talking about confederations
or RRs here - just basic BGP). He proposed the following alternative:
    -we have an AS with edge routers (running both iBGP and eBGP), and
transit routers (iBGP only).
    -we do full-mesh BGP between the edge routers, and only connect each
transit router to each edge router.
    -for 4 edge and 8 transit routers, this takes the number of BGP
connections from 12*11/2=66 to 4*3/2+8*4=38. Quite a significant change.

    Try as I might, I was unable to find a topology in which his
solution would fail. I'm hoping someone more experienced with BGP could
help me...

    Thank you,

-- 
Bogdan Sass
CCAI,CCSP,JNCIA-ER,CCIE #22221 (RS)
Information Systems Security Professional
"Curiosity was framed - ignorance killed the cat"

Blogs and organic groups at http://www.ccie.net



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