Service Manual
reduce the options. If a number of best paths is determined, this selection criteria is applied to group’s best to determine the ultimate
best path.
In non-deterministic mode (the bgp non-deterministic-med command is applied), paths are compared in the order in which
they arrive. This method can lead to Dell Networking OS choosing dierent best paths from a set of paths, depending on the order in
which they were received from the neighbors because MED may or may not get compared between the adjacent paths. In
deterministic mode, Dell Networking OS compares MED between the adjacent paths within an AS group because all paths in the AS
group are from the same AS.
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 dierent eBGP peers,
enable the bgp bestpath as-path multipath-relax command. A system error results if you congure 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 congured, 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.
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Border Gateway Protocol IPv4 (BGPv4)