Figure 17: Configuring Aggregate Addresses - Juniper JUNOSE 11.2.X BGP AND MPLS Configuration Manual

Figure 17: Configuring Aggregate Addresses

Copyright © 2010, Juniper Networks, Inc.
Figure 17 on page 59 illustrates an IPv4 network structure where you might use aggregation.
The following commands configure router LA and router SanJose so that router SanJose
advertises an IPv4 aggregate route, 172.24.0.0/16, for the more specific prefixes
172.24.1.0/24, 172.24.2.0/24, and 172.24.24.0/21.
To configure router LA:
host1(config)#router bgp 873
host1(config-router)#neighbor 10.2.2.4 remote-as 873
host1(config-router)#network 172.24.1.0 mask 255.255.255.0
host1(config-router)#network 172.24.2.0 mask 255.255.255.0
To configure router SanJose:
host2(config)#router bgp 873
host2(config-router)#neighbor 10.2.2.3 remote-as 873
host2(config-router)#neighbor 10.5.5.1 remote-as 17
host2(config-router)#network 172.24.24.0 mask 255.255.248.0
host2(config-router)#aggregate-address 172.24.0.0 255.255.224.0
As configured above, router SanJose advertises the more specific routes as well as the
aggregate route to router Boston. Alternatively, you can use the summary-only option
to configure router SanJose to suppress the more specific routes and advertise only the
aggregate route:
host2(config)#router bgp 873
host2(config-router)#neighbor 10.2.2.3 remote-as 873
host2(config-router)#neighbor 10.5.5.1 remote-as 17
host2(config-router)#network 172.24.24.0 mask 255.255.248.0
host2(config-router)#aggregate-address 172.24.0.0 255.255.224.0 summary-only
Each of these configurations sets the atomic-aggregate attribute in the aggregate route.
This attribute informs recipients that the route is an aggregate and must not be
deaggregated into more specific routes.
Aggregate routes discard the path information carried in the original routes. To preserve
the paths, you must use the as-set option. This option creates an AS-Set that consists
of all the AS numbers traversed by the summarized paths. The AS-Set is enclosed within
curly brackets; for example, {3, 2}. Each AS number appears only once, even if it appears
in more than one of the original paths. If you use the as-set option, the atomic-aggregate
Chapter 1: Configuring BGP Routing
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