Allied Telesis VERSION 5.4.3-2.6 manual Bgp deterministic-med BGP and BGP4+, Autonomous system AS

BGP and BGP4+ Commands

	bgp deterministic-med (BGP and BGP4+)
	Use this command to allow or disallow the switch to compare the Multi Exit Discriminator
	(MED) variable when choosing among routes advertised by different peers in the same
	autonomous system (AS).
	Use the bgp deterministic-medcommand to enable this feature to allow the comparison
	of MED variables when choosing among routes advertised by different peers in the same
	AS.
	Use the no variant of this command to disable this feature to disallow the comparison of
	the MED variable when choosing among routes advertised by different peers in the same
	AS.
Syntax [BGP/BGP4+]	bgp deterministic-med
	no bgp deterministic-med
Default [BGP/BGP4+]	Disabled
Mode [BGP/BGP4+]	Router Configuration
Usage [BGP/BGP4+]	When the bgp deterministic-medcommand is enabled, routes from the same AS are
	grouped together and ordered according to their MED values, and the best routes of each
	group are compared.
	The main benefit of this is that the choice of best route then does not depend on the order
	in which the routes happened to be received, which is rather random and arbitrary.
	To see how this works, consider the following set of bgp table entries, all for the same
	route:
	1: ASPATH 234, MED 120, internal, IGP metric to NEXT_HOP 40
	2: ASPATH 389, MED 190, internal, IGP metric to NEXT_HOP 35
	3: ASPATH 234, MED 245, external
	If bgp deterministic-medis not enabled, then entry 3: will be chosen, because it is an
	external route.
	But if BGP deterministic-MED is enabled, the entries will be grouped as follows:
	Group 1: 1: ASPATH 234, MED 120, internal, IGP metric to NEXT_HOP 40
		3: ASPATH 234, MED 245, external
	Group 2: 2: ASPATH 389, MED 190, internal, IGP metric to NEXT_HOP 35
	Note Routes from the same AS are grouped together and ordered by MED.

Entry 1: is chosen as the best route from Group 1, since this route has the lowest MED value. Entry 2 has to be the best route in Group 2, since this is the only route in that group. These two group winners are compared against each other, and Entry 2: is chosen as the best route because Entry 2: has the lower metric to next-hop.

	Software Reference Supplement for SwitchBlade® x8112, x908, x900 and x610 Series Switches
C613-50032-01 REV D	AlliedWare PlusTM Operating System - Software Version 5.4.3-2.6	3.29