Help with Confederation-RR-MPBGP

George, Wes at
Wed Jun 18 19:42:01 UTC 2014

On 6/18/14, 12:31 PM, "Philip Lavine" <source_route at> wrote:

>I guess my question is, is it best practice to confederate or use a route
>Basically I want to know what an ISP would do, not a test in a LAB.

One data point that you may find useful: If you find out later that you’ve
chosen incorrectly the first time around, it is FAR easier to change
*from* RRs *to* Confeds than it is to do the opposite. The AS migration
tools that you’d normally use to handle moving routers from one ASN to
another don’t work to migrate routers from a confed ASN to a normal iBGP
ASN setup, probably because the BGP machinery doesn’t know what to do with
the union of the changes those things make to BGP’s default behavior, so
you’re stuck with trying to find the least bad flag day way to handle
renumbering ASNs out of a confed. Doing it without major traffic impact is
pretty difficult since most of the options involve nuking BGP and
rebuilding it to punt routers from one ASN to another, and doing this on
multiple routers simultaneously in order to minimize the time when BGP is
offline on multiple devices due to ASN mismatches. Size of network of
course matters when considering whether this is really a potential issue
for you, but since you’re asking in terms of what an ISP would do vs what
works in a lab, considering large scale rather than today’s scale when
determining the exit strategy is pretty important.

Wes George

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