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Re: iBGP - Route Reflectors Vs. Confederations posted 08/07/2004
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At 4:57 PM -0700 8/6/04, nikolai wrote:
Any thoughts regarding choosing one versus the other in order to collapse
several ASs into a single one?

Well, it depends on the problem you want to solve. I find that in complex enterprises, where there may be very involved inter-region policies, confederations give a nice degree of control. Of course, this results in multiple AS, admittedly with only one seen by the outside world.


RRs tend to be more useful in a homogeneous service provider environment, although you may run into IGP scalability issues. A key document to read here is http://www.ietf.org/rfc/rfc3345.txt, which examines stability issues with respect to, among other things, hierarchical reflectors and possibly multiple IGP domains.


The single AS consists of about 100 BGP speakers, no possibility for full mesh, of course. IGP is OSPF, and the AS is used as a Transitive area.

I personally do not like multi-tier RRs and lots of Clusters.

They tend to be used by service providers that don't have much internal policy to implement, but need to keep their iBGP peerings at a reasonable number. Again, see RFC 3345. You also may want to look at whether you can improve scalability in the core by using MPLS rather than BGP speakers.


In addition, I
have the feeling that implementing routing policy would be easier with
Confederations, where we can see clearly the sub-AS PATH of the routes.
Having multiple geographical areas looks to me as a good argument in favor
of Confederations, since they all would require some local authority, and
common IGP with the backbone routers is not desired.  And the BGP design
looks much prettier...

Your input would be appreciated,

Nikolai Tsankov
niko@xxxxxxxxx