Juniper JUNOSE, Configuration Manual

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a result, all the routers receive updates learned by the area border routers from
external BGP speakers.
Figure 37: Disabling Synchronization
If synchronization is disabled, a BGP speaker propagates a BGP route learned from
a peer only if it is the best route to the prefix in the IP routing table. However, the
speaker does advertise the routes that it originates.
The following commands show how to configure routers Boston, NY, and Chicago
(shown in Figure 37 on page 135) with synchronization disabled for routers NY and
Boston. The
no synchronization command enables router NY to put the route to
192.56.0.0/16 in its IP routing table and advertise it to router Chicago without learning
about 192.56.00/16 from router Albany. The command also enables router Boston
to put the route to 192.30.0.0/16 in its IP routing table and advertise it to router LA
without learning about 192.30.00/16 from router Albany.
To configure router Boston:
host1((config)# router bgp 100
host1(config-router)# neighbor 2.2.2.2 remote-as 100
host1(config-router)# neighbor 4.4.4.1 remote-as 100
host1(config-router)# neighbor 1.1.1.2 remote-as 300
host1(config-router)# no synchronization
To configure router NY:
host2(config)# router bgp 100
host2(config-router)# neighbor 3.3.3.2 remote-as 200
host2(config-router)# neighbor 2.2.2.1 remote-as 100
host2(config-router)# neighbor 4.4.4.3 remote-as 100
host2(config-router)# no synchronization
To configure router Albany:
host3(config)# router bgp 100
host3(config-router)# neighbor 4.4.4.4 remote-as 100
host3(config-router)# neighbor 4.4.4.2 remote-as 100
host3(config-router)# no synchronization
Interactions Between BGP and IGPs
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Chapter 1: Configuring BGP Routing