Connectivity Guide
arrive, and selects the best paths. Paths for active routes are grouped in ascending order according to their neighboring external AS
number.
OS10 follows deterministic MED to select dierent best paths from a set of paths. This may depend on the order the dierent best paths
are received from the neighbors — MED may or may not get compared between adjacent paths. BGP best path selection is deterministic
by default.
The best path in each group is selected based on specic criteria—only one best path is selected at a time. If BGP receives more than one
best path, it moves on to the next list of valid paths, and continues until it reaches the end of the list.
When you congure the non-deterministic-med command, paths are compared in the order they arrive. OS10 follows this method
to select dierent best paths from a set of paths, depending on the order they were received from the neighbors—MED may or may not
get compared between the adjacent paths.
By default, the bestpath as-path multipath-relax command is disabled. This prevents BGP from load-balancing a learned route
across two or more EBGP peers. To enable load-balancing across dierent EBGP peers, enter the
bestpath as-path multipath-
relax command.
If you congure the bgp bestpath as-path ignore command and the bestpath as-path multipath-relax command at
the same time, an error message displays—only enable one command at a time.
More path support
More path (Add-Path) reduces convergence times by advertising multiple paths to its peers for the same address prex without replacing
existing paths with new ones. By default, a BGP speaker advertises only the best path to its peers for a given address prex.
If the best path becomes unavailable, the BGP speaker withdraws its path from its local router information base (RIB) and recalculates a
new best path. This situation requires both IGP and BGP convergence and is a lengthy process. BGP add-path also helps switch over to
the next new best path when the current best path is unavailable.
The Add-Path capability to advertise more paths is supported only on IBGP peers—it is not supported on EBGP peers or BGP peer groups.
Ignore router ID calculations
Avoid unnecessary BGP best path transitions between external paths under certain conditions. The bestpath router-id ignore
command reduces network disruption caused by routing and forwarding plane changes and allows for faster convergence.
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