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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 21. 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.
d
AS_CONFED_SEQUENCE has a path length of 1, no matter how many ASs are in the
AS_CONFED_SEQUENCE.
5
Prefer the path with the lowest ORIGIN type (IGP is lower than EGP, and EGP is lower than
INCOMPLETE).
6
Prefer the path with the lowest multi-exit discriminator (MED) attribute. The following criteria apply:
Border Gateway Protocol IPv4 (BGPv4)
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Troubleshooting
