How the bgp deterministic-med Command Differs from the bgp always-compare-med Command

Enabling the bgp deterministic-med command ensures the comparison of the MED variable when choosing routes advertised by different peers in the same autonomous system. Enabling the bgp always-compare-med command ensures the comparison of the MED for paths from neighbors in different autonomous systems.

 The bgp always-compare-med command is useful when multiple service providers or enterprises agree on a uniform policy for setting MED. Thus, for network X, if Internet Service Provider A (ISP A) sets the MED to 10, and ISP B sets the MED to 20, both ISPs agree that ISP A has the better performing path to X.

Note: The bgp deterministic-med and bgp always-compare-med commands are not enabled by default. Also, the two commands are separate; enabling one does not automatically enable the other.

Ref:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094925.shtml http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094431.shtml