Juniper BGP, Configuration Manual

Page: 68 / 748

configure multihop connections. By default, the one-hop limitation per EBGP peers
is enforced by the time-to-live attribute. You can override this default limit by using
the
ttl variable to specify the maximum number of hops to the peer.
In Figure 12 on page 32, router Boston and router LA are connected together through
router NY, rather than by a direct connection. Routers Boston and LA are configured
as external peers with the
neighbor ebgp-multihop command because no direct
connection exists between them. Because router NY is not a BGP speaker, static
routes are configured on routers Boston and LA. The configuration for router NY is
not shown, because it does not involve BGP.
Figure 12: Using EBGP-Multihop
The following commands achieve the BGP configuration.
To configure router Boston:
host1(config)# ip route 10.7.4.0 255.255.255.0 10.1.10.2
host1(config)# router bgp 100
host1(config-router)# neighbor 10.7.4.3 remote-as 300
host1(config-router)# neighbor 10.7.4.3 ebgp-multihop
To configure router LA:
host2(config)# ip route 10.1.10.0 255.255.255.0 10.7.4.4
host2(config)# router bgp 300
host2(config-router)# neighbor 10.1.10.1 remote-as 100
host2(config-router)# neighbor 10.1.10.1 ebgp-multihop
neighbor ebgp-multihop
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Use to configure BGP to accept route updates from external peers in networks
that are not directly connected to the local peer.
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If you specify a BGP peer group by using the peerGroupName argument, all the
members of the peer group inherit the characteristic configured with this
command unless it is overridden for a specific peer.
■
Any external BGP peering that is not resolved by a connected route is treated as
a multihop. Configurations with loopback-to-loopback external BGP peering
require the
neighbor ebgp-multihop command to work properly. In these
configurations, the neighbor remote-as command is issued with the address of
a loopback interface.
32 ■
Configuring BGP Peer Groups
JUNOSe 11.1.x BGP and MPLS Configuration Guide