IBGP Question --- Router Reflector or iBGP Mesh

Philip Smith pfs at cisco.com
Tue Jan 11 11:51:36 UTC 2005

Hi Eric,

Eric Kagan said the following on 11/01/2005 11:03:
>>Correct, route reflector's main advantage is scalability and 
>>if you're thinking to evolve into a larger network with 
>>dedicated access and core routers, route reflectors are a far 
>>better option than full mesh, though perhaps not from the start. 
> Does anyone have any input on when this does make sense ?  We have 3 Main IP
> pops with upstream BGP at each and 4 internal BGP sessions.  I am looking to
> add 2 new routers so there will be about 7 sessions on each border router.
> They are 7206VXR all 256MB RAM just acting as border.  No customer circuits,
> etc.  Is it time to look at route reflectors at this point ?  Any input or
> guidelines for making a smooth transition from Full mesh ?

Well, my preference is to start with route reflectors pretty much from 
day one. Let's face it, one day you will have to migrate that full mesh 
iBGP to route reflector. Why do the work of migration when you can start 
off at the beginning using route reflectors. One less job to do, one 
less potential network disruption, happy customers,...

Many of the ISPs I've worked with around the world have followed this 
path - and they are quite happy. I really think there is absolutely no 
need to consider full mesh iBGP any more. I wouldn't go as far as saying 
it's history, but I find it very hard to make an operational case for 
deploying full mesh iBGP any more.

As for guidelines for transition, check out the BGP tutorials which have 
been given at the recent NANOGs. It's really very simple to do, and you 
are lucky as you have relatively few routers to migrate.

Hope this helps,


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