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9.9 | ![]() |
Redundancy, Symmetry, and Load Balancing | |
9.9.5 | ![]() |
Load balancing |
Load balancing is the capability to divide data traffic over multiple
connections. A BGP speaker may learn two identical EBGP paths for a
prefix from a neighboring AS. If this happens, it will choose the path with the lowest
route ID as the best path. This best path is installed in the IP
routing table. If BGP multipath support is enabled and the EBGP paths
are learned from the same neighboring AS, the best path may not
be chosen. Instead, multiple paths are installed in the IP routing table.
To enable BGP load balancing over equal cost paths, use the maximum-paths command, which has the following syntax:
BGP supports a maximum of six paths per destination, but only if they are sourced from the same AS. By default, BGP will install only one path to the IP routing table. Figure On the other hand, the path for inbound traffic to reach the local networks, NetB and NetC, depends on how these networks are advertised. If NetC is advertised over the New York link only, then incoming traffic toward NetC will take the New York link. Similarly, if NetB is advertised over the San Francisco link only, traffic toward NetB will take the San Francisco link.
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