H3C Technologies H3C S12500-X Series Switches - Manual (Page 194)

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The system supports BGP load balancing based on route recursion. If multiple recursive routes to
the same destination are load balanced (suppose three direct next hop addresses), BGP generates
the same number of next hops to forward packets. BGP load balancing based on route recursion
is always enabled by the system rather than configured by using commands.
• BGP load balancing through route selection.
IGP routing protocols, such as RIP and OSPF, compute the metrics of routes, and implement load
balancing over the 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 perform load balancing according to the
metrics of routes. BGP implements load balancing over the routes that meet the following
requirements:
{
The routes have the same AS_PATH, ORIGIN, LOCAL_PREF, and MED attributes.
{
The routes are all reflected or not reflected by the route reflector.
BGP does not use the route selection rules described in "
1060H
BGP route selection " for load balancing.
Figure 50 Network diagram
In
1061H
Figure 50 , 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 and other attributes changed to
those of the best route.
NOTE:
BGP load balancing is applicable between EBGP peers, between IBGP peers, and between
confederations.
304B
Settlements for problems in large-scale BGP networks
You can use the following methods to facilitate management and improve route distribution efficiency on
a large-scale BGP network.
• Route summarization