Prefixes Originating In An As; Figure 13: Prefixes Originating In An As - Juniper JUNOSE 11.2.X BGP AND MPLS Configuration Manual

Prefixes Originating in an AS

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By default, BGP does not advertise any route unless the router's IP routing table also
contains the route.
Use the network command to configure a router with the prefixes that originate within
its AS. Thereafter the router advertises these configured prefixes with the origin attribute
set to IGP. See "Understanding the Origin Attribute" on page 114 for more information
about origins. Figure 13 on page 51 shows a network structure of three autonomous
systems, each with a router that originates certain prefixes.

Figure 13: Prefixes Originating in an AS

The following commands configure router NY:
host1(config)#router bgp 300
host1(config-router)#neighbor 10.2.25.1 remote-as 100
host1(config-router)#neighbor 10.4.4.1 remote-as 400
host1(config-router)#network 192.168.33.0 mask 255.255.255.0
The following commands configure router Boston:
host2(config)#router bgp 100
host2(config-router)#neighbor 10.2.25.2 remote-as 300
host2(config-router)#neighbor 10.3.3.1 remote-as 400
host2(config-router)#network 172.19.0.0
Notice that a mask was not specified for the prefix originating with router Boston. The
natural mask is assumed for networks without a mask.
The following commands configure router LA:
host3(config)#router bgp 400
host3(config-router)#neighbor 10.3.3.2 remote-as 100
host3(config-router)#neighbor 10.4.4.2 remote-as 300
host3(config-router)#network 172.28.8.0 mask 255.255.248.0
Use to specify the prefixes in its AS that the BGP speaker advertises.
BGP advertises the specified prefix only if a non-BGP route to the prefix exists in the
IP forwarding table. If the non-BGP route does not exist when you issue the network
Chapter 1: Configuring BGP Routing
51