HP ProCurve Secure Router 7203 dl Advanced Management And Configuration Manual page 689

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
When the ProCurve Secure Router receives a route from a neighbor, it sets the
update source as the forwarding interface for the route. Because the loopback
interface becomes the forwarding interface rather than a specific WAN inter-
face, the router automatically distributes packets over all links to the neighbor.
A loopback interface also adds stability to the network because it is always
up as long as a path exists between the router and the neighbor. In this way,
the router sidesteps problems with unstable links or flapping interfaces.
Hop 1 Hop 2
WAN
interface
ISP
Router A
Network 1
Loopback
interface
Figure 13-16. EBGP Multihop
N o t e s
Your must inform your ISP if you are using a loopback interface as the update
source so that its IT staff can correctly configure the ISP router to connect to
your router.
When you use a loopback interface as the update source, you add a hop
between neighbors. (See Figure 13-16.) You must enable the multihop func-
tion:
Syntax: ebgp-multihop <hop count>
The hop count can be between 1 and 254.
For example, enter the following commands:
ProCurve(config)# interface loopback 1
ProCurve(config-loopback 1)# ip address 2.2.2.2 /32
ProCurve(config-loopback 1)# exit
ProCurve(config)# router bgp 1
ProCurve(config-bgp)# neighbor 1.1.1.1
ProCurve(config-bgp-neighbor)# update-source loopback 1
ProCurve(config-bgp-neighbor)# ebgp-multihop 2
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