Figure 26: Communities - Juniper JUNOSE SOFTWARE FOR E SERIES 11.3.X - BGP AND MPLS CONFIGURATION GUIDE 2010-10-12 Configuration Manual

Figure 26: Communities

Copyright © 2010, Juniper Networks, Inc.
convenient way to categorize groups of routes to facilitate the use of routing policies.
The community attribute consists of four octets, but it is common practice to designate
communities in the AA:NN format. The autonomous system number (AA) comprises the
higher two octets, and the community number (NN) comprises the lower two octets.
Both are expressed as decimal numbers. For example, if a prefix in AS 23 belongs to
community 411, the attribute can be expressed as 23:411. Use the ip bgp-community
new-format command to specify that the show commands display communities in this
format.
Use the set community command in route maps to configure the community attributes.
By default, the community attribute is not sent to BGP peers. To send the community
attribute to a neighbor, use the neighbor send-community command.
Consider the network structure shown in Figure 26 on page 91. The following sample
configurations illustrate some of the capabilities of using the community attribute.
The following commands configure router NY to apply route map setcomm to routes
going out to 10.72.4.3. If the community attribute of such a route matches instance 10 of
the route map, router NY sets the community attribute to 31:15. All locally originated
routes will match this instance of the route map.
host1(config)#router bgp 31
host1(config-router)#network 10.16.22.0 mask 255.255.254.0
host1(config-router)#neighbor 10.72.4.3 remote-as 425
host1(config-router)#neighbor 10.72.4.3 send-community
host1(config-router)#neighbor 10.72.4.3 route-map setcomm out
host1(config-router)#exit
host1(config)#ip as-path access-list 1 permit ^$
host1(config)#route-map setcomm permit 10
host1(config-route-map)#match as-path 1
host1(config-route-map)#set community 31:15
The following commands configure router LA to apply route map matchcomm to routes
coming in from 10.72.4.2. If the community attribute of such a route matches instance 10
of the route map, router LA sets the weight of the route to 25.
host2(config)#router bgp 425
host2(config-router)#network 172.24.160 mask 255.255.224.0
host2(config-router)#neighbor 10.72.4.2 remote-as 31
host2(config-router)#neighbor 10.72.4.2 send-community
Chapter 1: Configuring BGP Routing
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