C613-50631-01 Rev A Command Reference for IE340 Series 1315
AlliedWare Plus™ Operating System - Version 5.5.3-0.x
BGP AND BGP4+ COMMANDS
BGP
ALWAYS-COMPARE-MED
bgp always-compare-med
Overview This command enables BGP to compare the Multi Exit Discriminator (MED) for
paths from neighbors in different autonomous systems.
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 variant of this command disallows the comparison.
Syntax
bgp always-compare-med
no bgp always-compare-med
Default By default this feature is disabled.
Mode Router Configuration
Example
awplus# configure terminal
awplus(config)# router bgp 100
awplus(config-router)# bgp always-compare-med
Related
commands
bgp bestpath med
bgp bestpath as-path ignore
bgp bestpath compare-routerid
bgp deterministic-med
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