Comment 28 for bug 1650219

Reviewed: https://review.opencontrail.org/27904
Committed: http://github.org/Juniper/contrail-controller/commit/c537a30a392a250ce728f5d5d4a7d57f89618124
Submitter: Zuul (<email address hidden>)
Branch: R3.1

commit c537a30a392a250ce728f5d5d4a7d57f89618124
Author: jayaramsatya <email address hidden>
Date: Wed Jan 11 19:33:37 2017 +0530

Problem:
For vcenter only mode, the agent replies arp with the physical intf mac address for the VN's gateway ip.
When vm migrates to a different esxi host as part of vmotion,vcenter plugin binds it to the new contrail-compute-vm,whose physical intf mac is different. But the vm still hold the old mac address for the gateway ip in the arp table.
Until the old mac address gets flushed and the new mac is learnt for the gateway ip, the traffic is lost from the vm for a different subnet.
Solution:
Whenever VM migrates to new esxi host. and upon creation of VM interface
Arp module will listen on route update. after getting the route update
send the gratious arp for the Gateway IP.
closes-bug:#1650219

Change-Id: I6bf4bab98c956bead866d22b7c8e8960419315b4