Dell S4820T, Configuration Manual

Page: 203 / 1178

NOTE: The
bgp bestpath as-path multipath-relax
command is disabled by default,
preventing BGP from load-balancing a learned route across two or more eBGP peers. To enable
load-balancing across different eBGP peers, enable the
bgp bestpath as-path multipath-
relax
command. A system error results if you configure the
bgp bestpath as-path ignore
command and the
bgp bestpath as-path multipath-relax
command at the same time.
Only enable one command at a time.
The following illustration shows that the decisions BGP goes through to select the best path. The list
following the illustration details the path selection criteria.
Figure 24. BGP Best Path Selection
Best Path Selection Details
1. Prefer the path with the largest WEIGHT attribute.
2. Prefer the path with the largest LOCAL_PREF attribute.
3. Prefer the path that was locally
Originated via a network
command,
redistribute
command or
aggregate-address
command.
a. Routes originated with the
Originated via a network
or
redistribute
commands are
preferred over routes originated with the
aggregate-address
command.
4. Prefer the path with the shortest AS_PATH (unless the
bgp bestpath as-path ignore
command
is configured, then AS_PATH is not considered). The following criteria apply:
a. An AS_SET has a path length of 1, no matter how many ASs are in the set.
b. A path with no AS_PATH configured has a path length of 0.
c. AS_CONFED_SET is not included in the AS_PATH length.
Border Gateway Protocol IPv4 (BGPv4)
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