Allied Telesis VERSION 5.4.3-2.6 manual Bgp always-compare-med BGP and BGP4+

BGP and BGP4+ Commands

bgp always-compare-med (BGP and BGP4+)

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 system (AS). Use the bgp always-compare-modefrom different ASs.

routes from the same autonomous command to allow comparison of MEDs

A path with a lower MED value is preferred. For example, if the bgp table contains the following entries, and the bgp always-compare-medcommand 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-medwas 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-medcommand. See the bgp deterministic-med (BGP and BGP4+) command on page 3.29 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 and BGP4+)

bgp bestpath as-path ignore (BGP and BGP4+) bgp bestpath compare-routerid (BGP and BGP4+) bgp deterministic-med (BGP and BGP4+)

	Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches
3.14	AlliedWare PlusTM Operating System - Software Version 5.4.3-2.6	C613-50032-01 REV D