[c-nsp] ME3600 iBGP to RR

[Adam Vitkovsky]

Hi Mark,

> From: Mark Tinka [mailto:mark.tinka at seacom.mu]
> Sent: 06 March 2015 20:45
> My deployment for the ME3600X where BGP-SD shines is in rings, i.e.,
> east-west topologies. BGP-SD works great here, because iBGP routes
> (including 0/0 and ::/0) installed in the FIB have only one way to go
> anyway. So my BGP-SD route-maps are not that simple, but they are also
> very, very short.

So I imagine you also need to permit customer PIs and PAs into FIB otherwise customers hanging off of MEs in a common ring would not be able to communicate directly but would rather need to follow the default route towards the closest box that holds the full routing information.
So you are indeed using communities to identify what can leak into FIB -otherwise the route-map wold have to be updated on all routers each time a new customer connection is added.

That kind of solves my dispute as to which solution BGP-SD/PW to full-BGP is more "routing efficient"
And indeed BGP-SD allows for more efficient Intra-AS routing.
It's just in my head the PW between CE and speaker with full Inet BGP table guaranties that nothing wrong ever happens, whereas the BGP-SD is like asking for trouble (because what can break will break, eventually, in a long run).  

> north-south topology. In such scenarios, you can't avoid forwarding
> inefficiencies and their associated risks when limiting what enters the
> FIB, be it via BGP-SD, max-prefix or no BGP altogether.

Indeed anytime you are diverging from a "bgp full-mesh" type of routing information in FIB you will introduce inefficiencies. 


adam
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