Comment 0 for bug 1680005

MED is an interesting option to provide a backbone IGP metric visibility to contrail in an option B framework. There are usually knobs on router OS (ex. JUNOS) to copy NH IGP metric to prefix MED attributes.

This choice drives two enhancements w.r.t. current MED implementation on contrail:

 - ER1: MED may actually be received (and need to be compared) with empty AS. The UC is simply to support static routes redistributed in BGP on PEs, while contrail is in same AS as backbone.

 - ER2: MED may be used with different neighbor AS => we should be able to have a knob that allows contrail to operate in "always-compare-med" mode. The UC is multihomed prefixes where neighboring AS can be different, with the objective to forward traffic to the closest neighbor (MED=IGP)