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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