Multicast and Routing Guide K/KA/KB.15.15

Enables the comparison of the Multi Exit Discriminator (MED) for paths from
neighbors in different autonomous systems. To disallow the comparison, use the no
form of this command.
The MED is one of the parameters that is considered when selecting the best path
among many alternative paths. The path with a lower MED is preferred over a path
with a higher MED. During the best-path selection process, MED comparison is
done only among paths from the same autonomous system. The bgp
always-compare-med command is used to change this behavior by enforcing
MED comparison between all paths, regardless of the autonomous system from
which the paths are received.
Specifying the number of times an AS number can appear in AS_PATH
Syntax:
[no] bgp allowas-in num-loops
Specifies the number of times an Autonomous System number can appear in the
AS_PATH. Use the no form of the command to set the parameter to its default value
of ‘1’.
Configuring BGP to not consider AS_PATH
Syntax:
[no] bgp bestpath as-path-ignore
Configures Border Gateway Protocol (BGP) to not consider the autonomous system
(AS)-path during best path route selection. To restore default behavior and configure
BGP to consider the AS-path during route selection, use the no form of this command.
By default, the AS-path is considered during BGP best path selection.
Breaking ties between routes based on originator ID value
Syntax:
[no] bgp bestpath compare-originator-id
Specifies to break ties between routes based the Originator ID value instead of the
neighbor’s router ID. Use the no form of the command to not compare routes based
on originator ID.
Comparing identical routes received from different external peers
Syntax:
[no] bgp bestpath compare-router-id
To configure a Border Gateway Protocol (BGP) routing process to compare identical
routes received from different external peers during the best path selection process
and to select the route with the lowest router ID as the best path, use the bgp
bestpath compare-routerid command in router configuration mode. To
return the BGP routing process to the default operation, use the no form of this
command.
The behavior of this command is disabled by default; BGP selects the route that
was received first when two routes with identical attributes are received.
Configuring BGP policy globally 293