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212 | Border Gateway Protocol IPv4 (BGPv4)
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Figure 10-4. 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.
• Routes originated with the
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:
• An AS_SET has a path length of 1, no matter how many ASs are in the set.
• A path with no AS_PATH configured has a path length of 0.
• AS_CONFED_SET is not included in the AS_PATH length.
Highest
Weight
Highest
Local Pref
Locally
Originated
Path
Shortest
AS Path
Lowest
Origin
Code
Lowest
MED
Learned
via EBGP
Lowest
Cluster ID
List
from
Lowest
Router ID
from
Lowest
Neighbor
Addr
Lowest
NEXT-HOP
Cost
A Single Route is Selected and Installed in the Routing Table
Tie Breakers
No, or Not Resulting in a Single Route