HP VPN Firewall Appliances Appendix Protocol Reference

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{ IGP routing protocols, such as RIP and OSPF, compute metrics of routes, and then implement
load balancing over routes with the same metric and to the same destination. The route selection
criterion is metric.
{ BGP has no route computation algorithm, so it cannot implement load balancing according to
metrics of routes. However, BGP has abundant route selection rules, through which, it selects
available routes for load balancing and adds load balancing to route selection rules.
BGP implements load balancing only on routes that have the same AS_PATH, ORIGIN,
LOCAL_PREF and MED, rather than using the route selection rules as described in "BGP route
sel
ection."
Figure 27 Network diagram
In Figure 27, Router A and Router B are IBGP peers of Router C. Router D and Router E both advertise a
route 9.0.0.0 to Router C. If load balancing with a maximum number of two routes is configured on
Router C, and the two routes have the same AS_PATH, ORIGIN, LOCAL_PREF, and MED, Router C
installs both the two routes to its routing table for load balancing. After that, Router C forwards to Router
A and Router B a single route that has NEXT_HOP changed to Router C without changing other
attributes.
NOTE:
BGP load balancing is applicable between EBGP peers, between IBGP peers, and between
confederations.
Settlements for problems in large-scale BGP
networks
For easy management and route distribution efficiency, use the following methods on a large-scale BGP
network:
• Route summarization
Route summarization can reduce the BGP routing table size by advertising summary routes rather
than more specific routes.