Taken from http://www.cisco.com/en/US/docs/ios/iproute/configuration/guide/irp_bgp_link_band.html

The link bandwidth extended community attribute is a 4-byte value that is configured for a link that on the demilitarized zone (DMZ) interface that connects two single hop eBGP peers. The link bandwidth extended community attribute is used as a traffic sharing value relative to other paths while forwarding traffic. Two paths are designated as equal for load balancing if the weight, local-pref, as-path length, Multi Exit Discriminator (MED), and Interior Gateway Protocol (IGP) costs are the same.