HP 7102dl - ProCurve Secure Router Configuration Manual page 812

IP Routing—Configuring RIP, OSPF, BGP, and PBR
Configuring BGP
15-86
When multihoming, you can configure one BGP interface to advertise one set
of local networks to one ISP and another BGP interface to advertise another
set to another ISP. In this way, you can attempt to force the ISPs to load balance
incoming traffic across your two connections. (However, this method is
uncertain. See "Load Balancing" on page 15-76 for more information on load
balancing.)
For example, your organization uses private networks 192.168.1.0 /24 through
192.168.16.0 /24. You could configure one prefix list to allow the advertisement
of networks 192.168.1.0 /24 through 192.168.7.0 /24:
ProCurve(config)# ip prefix-list ISP1Out seq 1 permit 192.168.0.0/21 ge 24 le 24
You would then apply the prefix list to routes advertised to one BGP neighbor:
ProCurve(config)# router bgp 1
ProCurve(config-bgp)# neighbor 10.1.1.1
ProCurve(config-bgp-neighbor)# prefix-list ISP1Out out
You could then configure another prefix list that allows the second half of the
networks and apply the list to the second neighbor:
ProCurve(config)# ip prefix-list ISP2Out seq 1 permit 192.168.8.0/21 ge 24 le 24
ProCurve(config)# router bgp 1
ProCurve(config-bgp)# neighbor 10.2.2.2
ProCurve(config-bgp-neighbor)# prefix-list ISP2Out out
Load Balancing Outgoing Traffic by Preventing an Interface from
Learning Specific Routes. In a multihomed network, you can configure
load balancing for outbound traffic by controlling which external routes each
router or router interface learns. Divide all external networks into the number
of connections that your network has to the Internet. Assign a section of these
external networks to each BGP interface and filter out all other traffic on that
interface.