[c-nsp] I-BGP/IGP question

Shawn Zandi szmetal at gmail.com
Tue Sep 16 02:48:02 EDT 2014

In case you have a router in the middle that doesnt speak BGP, then traffic
will be blackholed (unless you redistibute that BGP route into your IGP,
check the traditional cisco bgp synchronization rule)

The answer is simple, enable bgp on every hop, or create a bgp-free core
using MPLS or tunneling mechanism that route lookup would not be necessary
in transit nodes.


On Mon, Sep 15, 2014 at 9:55 PM, Wes Smith <f287cd76 at opayq.com> wrote:

> 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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