Bgp Always-Compare-Med - Allied Telesis SwitchBlade x908 Series Software Reference Manual

bgp always-compare-med

This command enables BGP to compare the Multi Exit Discriminator (MED) for paths from
neighbors in different autonomous systems. By default this feature is disabled.
Multi Exit Discriminator (MED) is used in best path selection by BGP. MED is compared after
BGP attributes weight, local preference, AS-path and origin have been compared and are equal.
By default, MED comparison is done only among routes from the same autonomous system
(AS). Use the bgp always-compare-mode command to allow comparison of MEDs from
different ASs.
A path with a lower MED value is preferred. For example, if the bgp table contains the
following entries, and the bgp always-compare-med command has been issued to enable
this feature:
Route1: as-path 400, med 300
Route2: as-path 200, med 200
Route3: as-path 400, med 250
Route1 is compared to Route2. Route2 is best of the two (lower MED). Next, Route2 is
compared to Route3 and Route2 is chosen best path again (lower MED). If always-
compare-med was disabled, MED is not taken into account when Route1 and Route2 are
compared, because of different ASs and MED is compared for only Route1 and Route3. In this
case, Route3 would be the best path. The selected route is also affected by the bgp
deterministic-med command. See the bgp deterministic-med command for details.
If this command is used to compare MEDs for all paths, it should be configured on every BGP
router in the AS.
The no form disallows the comparison.
Syntax bgp always-compare-med
no bgp always-compare-med
Router mode
Mode
Example
awplus(config-router)#
bgp bestpath med
Related Commands
bgp bestpath as-path ignore
bgp bestpath compare-routerid
bgp deterministic-med
C613-50007-01 REV B
awplus# configure terminal
awplus(config)# router bgp 100
bgp always-compare-med
Software Reference for SwitchBlade® x908, x900 and x600 Series Switches
TM
AlliedWare Plus Operating System - Software Version 5.3.1
BGP Commands
38.7