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Configuring BGP
Configuring Advanced BGP Features
IPC-327
Cisco IOS IP Configuration Guide
Configuring the Router to Consider a Missing MED as Worst Path
To configure the router to consider a path with a missing MED attribute as the worst path, use the
following command in router configuration mode:
Selecting Path Based on MEDs from Other Autonomous Systems
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.
By default, during the best path selection process, MED comparison is done only among paths from the
same autonomous system. You can allow comparison of MEDs among paths regardless of the
autonomous system from which the paths are received. To do so, use the following command in router
configuration mode:
Configuring the Router to Use the MED to Choose a Path from Subautonomous
System Paths
To configure the router to consider the MED value in choosing a path, use the following command in
router configuration mode:
The comparison between MEDs is only made if there are no external autonomous systems in the path
(an external autonomous system is an autonomous system that is not within the confederation). If there
is an external autonomous system in the path, then the external MED is passed transparently through the
confederation, and the comparison is not made.
The following example compares route A with these paths:
path= 65000 65004, med=2
path= 65001 65004, med=3
path= 65002 65004, med=4
path= 65003 1, med=1
Command Purpose
Router(config-router)# bgp bestpath med
missing-as-worst
Configures the router to consider a missing MED as having a
value of infinity, making the path without a MED value the
least desirable path.
Command Purpose
Router(config-router)# bgp always-compare-med
Allows the comparison of MEDs for paths from neighbors in
different autonomous systems.
Command Purpose
Router(config-router)# bgp bestpath med confed
Configures the router to consider the MED in choosing a path
from among those advertised by different subautonomous
systems within a confederation.