So what about iBGP itself? So how do you scale iBGP? We've made good use of communities under the customer requirements. To scale iBGP most of the time you're going to have a route reflector and this will scale your iBGP mesh. So in transit networks your core routers, the route reflectors will carry the full BGP tables but the edge and aggregation routers will only carry domestic prefixes and customers so prefixes which are local to that router. And this way you are able to make sense of what's happening on your network. This is an example of how we'd configure the root reflector: it's in AS100 and a lot of it is what we've seen already so you have a neighbor, or it's a peer group and description is anybody who is inside this peer group is a root reflector client. And this is the route map that we are applying on the outbound direction and it's going to match particular communities: ten, eleven, twelve, thirteen, fourteen, fifteen and sixteen so all prefixes coming from the domestic network and IXP as sent out. But you must not forget to send the community to each iBGP peer. You have to add the send-community so that these communities are propagated in the iBGP sessions. So you just have a simple root map and you're applying a community match. You don't have prefix lists. You don't have AS path filters or any other complicated policy and once a prefix belongs to the right community then it has access across the backbone determined by what that community should be doing.

© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.

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