Figure 28: Configuring Next-Hop Processing
Router Memphis advertises 172.24.160/19 with a next hop of 10.2.2.2 to router Jackson.
Router Jackson advertises this same network externally to router Topeka with a next hop
of 10.1.13.1.
Router Topeka advertises network 192.168.32.0/19 with a next hop of 10.1.13.2 to router
Jackson. Because this network originates outside AS 604, router Jackson then internally
advertises this network (192.168.32.0/19) to router Memphis with the same next hop,
10.1.13.2 (the IP address of the external BGP speaker that advertised the route).
When router Memphis has traffic destined for 192.168.32.0/19, it must be able to reach
the next hop by means of an IGP, because it has no direct connection to 10.1.13.2.
Otherwise, router Memphis will drop packets destined for 192.168.32.0/19 because the
next-hop address is not accessible. Router Memphis does a lookup in its IP routing table
to determine how to reach 10.1.13.2:
Next HopDestination
10.2.2.110.1.13.0/24
The next hop is reachable through router Jackson, and the traffic can be forwarded.
The following commands configure the routers as shown in Figure 28 on page 106:
To configure router Jackson:
host1(config)#router bgp 604
host1(config-router)#neighbor 10.1.13.2 remote-as 25
host1(config-router)#neighbor 10.2.2.2 remote-as 604
host1(config-router)#network 192.168.22.0 mask 255.255.254.0
To configure router Memphis:
host2(config)#router bgp 604
host2(config-router)#neighbor 10.2.2.1 remote-as 604
host2(config-router)#network 172.24.160.0 mask 255.255.224.0
Copyright © 2010, Juniper Networks, Inc.106
JunosE 11.2.x BGP and MPLS Configuration Guide
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