path selection enhancements for MED attribute

[richard roberts]

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)

The corresponding UI change is tracked via bug 1697321.

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/32735
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/32736
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/32737
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/32735
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/32736
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Review in progress for https://review.opencontrail.org/32737
Submitter: Nischal Sheth (<email address hidden>)

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/32735
Committed: http://github.com/Juniper/contrail-controller/commit/f4102320362b63dcd64febe6d52766f796d4530c
Submitter: Zuul (<email address hidden>)
Branch: master

commit f4102320362b63dcd64febe6d52766f796d4530c
Author: Nischal Sheth <email address hidden>
Date: Thu Jun 8 14:02:58 2017 -0700

Implement knob to always compare med

Always compare med even if paths have an empty AS path or are learnt
from different neighbor ASes if the knob is set.

Change-Id: Ia831ae01ec7deb1359e9842a0220264923788fa3
Closes-Bug: 1680005

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/32736
Committed: http://github.com/Juniper/contrail-controller/commit/b8be6ee525da2b9b588ffe821b93f9dc24de1c56
Submitter: Zuul (<email address hidden>)
Branch: R4.0

commit b8be6ee525da2b9b588ffe821b93f9dc24de1c56
Author: Nischal Sheth <email address hidden>
Date: Thu Jun 8 14:02:58 2017 -0700

Implement knob to always compare med

Always compare med even if paths have an empty AS path or are learnt
from different neighbor ASes if the knob is set.

Change-Id: Ia831ae01ec7deb1359e9842a0220264923788fa3
Closes-Bug: 1680005

[OpenContrail Admin (ci-admin-f)]

Reviewed: https://review.opencontrail.org/32737
Committed: http://github.com/Juniper/contrail-controller/commit/ccfd6d7c359567435a8eefe0748e37ba2eff79a7
Submitter: Zuul (<email address hidden>)
Branch: R3.2

commit ccfd6d7c359567435a8eefe0748e37ba2eff79a7
Author: Nischal Sheth <email address hidden>
Date: Thu Jun 8 14:02:58 2017 -0700

Implement knob to always compare med

Always compare med even if paths have an empty AS path or are learnt
from different neighbor ASes if the knob is set.

Change-Id: Ia831ae01ec7deb1359e9842a0220264923788fa3
Closes-Bug: 1680005