[c-nsp] I-BGP/IGP question

Wes Smith f287cd76 at opayq.com
Thu Sep 18 17:46:32 EDT 2014

Thanks everyone. This discussion confirms what we thought,  All routers in the transit path between E-BGP edge devices need to be running I-BGP. In our case, we can't do that.  Our internal routers are Cat6509 with standard sup720.  Not enough ram/tcam. 
So the GRE tunnels between our EBGP edge will do the job... Thanks again
From: f287cd76 at opayq.com
To: cisco-nsp at puck.nether.net
Subject: I-BGP/IGP question
Date: Tue, 16 Sep 2014 00:55:40 -0400

I've often wondered how large ISPs handle some basic IGP design issues re routing between I-BGP nodes in the network. 
For example ..  assume two BGP routers connected over a backbone running some kind of IGP I-BGP uses the local IGP to route to other I-BGP nodes within the ASThe I-BGP next-hop address is the Egress I-BGP node (normally) or the IBPG peer loopbackBest practice says to keep the IGP small, for example just the I-BGP loopbacks So a potential routing table entry in router BGP1 would be something like 
Rtr BGP1 can reach ' via, where is router BGP-2s loopback address and BGP-2 is the egress router
So far so good. .. I understand all this part.  But my puzzle is .. for this to work, the IGP would also need to have a route for   so it can route it to my other IBGP router at my IGP doesn't have a route for as I don't redistribute BGP into IGPSo catch-22 . 
I've resolved this internally using tunnels between my I-BGP routers and using next-hop-self. But I'm pretty small scale ..   How do larger organisations do it? 
I'm guessing MPLS TE or other tunnels between the POPs .. but would like to hear from some folks that have done it.Thanks WS
(apologies for any dups..) 

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