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Chapter 9

BGP Scalability and Advanced Features

Last read 00:00:05, hold time is 180,

keepalive interval is 60 seconds

Minimum time between advertisement runs is 5 seconds

Received 14 messages, 0 notifications, 0 in queue

Sent 12 messages, 0 notifications, 0 in queue

Prefix advertised 0, suppressed 0, withdrawn 0

Connections established 2; dropped 1

Last reset 12:10:16, due to User reset

53 accepted prefixes consume 32 bytes

0 history paths consume 0 bytes

Confederations

confederation is another extension of using route reflectors. The

difference is that instead of looking from the iBGP standpoint, BGP now
looks at the entire autonomous system. Using confederations allows you to
divide an AS into sub-ASes running eBGP between them. A confederation is
a conglomerate of all the sub-ASes being advertised to the outside world as
one giant AS. To the outside world, a confederation is invisible.

Confederations are a little more difficult to configure than route reflec-

tors, unfortunately. The reason I say this is that when using confederations,
you must perform a reconfiguration on each of the routers in the AS and also
let non-optimal routes seep in to the BGP table, creating routing problems in
your network. The way around learning the non-optimal routes is to recon-
figure your BGP policies on each individual router participating in the
confederation.

When you use confederations, you use the router bgp command to con-

figure all of the sub-AS routers with their own BGP ASN. You then configure
the confederation's ASN on each of the routers using the bgp confederation
identifier

command. Next, you configure each of the peer sub-ASNs using

the bgp confederation peers command.

To get a better idea of how to configure confederations, let's examine Fig-

ure 9.3. You see that all of the routers are part of confederation AS 31,400,
but it been broken down into three sub-ASes.

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