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[Alan Pevec <1184696@xxxxxxxxxxxxxxxxxx>]

** Changed in: neutron
       Status: Fix Committed => Fix Released

** Changed in: neutron
     Assignee: (unassigned) => Adin Scannell (amscanne)

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https://bugs.launchpad.net/bugs/1184696

Title:
  GRE tunneling is broken if hosts are on multiple subnets (multi-homed)

Status in OpenStack Neutron (virtual network service):
  Fix Released

Bug description:
  Basic setup:
  * Bunch of hosts on subnet X
  * Host on subnet X and subnet Y (controller)
  * Bunch of hosts on subnet Y

  If local_ip for controller is from subnet X, then GRE tunnels are
  broken from controller to subnet Y.

  -- more detail --

  Because you can only specify a single local_ip when using GRE
  tunneling in openvswitch and this information is propagated to all
  hosts regardless of their subnet -- allowing GRE to choose the
  local_ip for tunnels results in one-directional flows because the IP
  won't be recognized (as one or more hosts may be sending traffic on an
  IP that is not their recognized local_ip).

  There is a pretty straight-forward fix -- the local_ip should be
  specified for all GRE tunnels, that way all traffic will originate
  from the IP that the hosts in the cluster are aware of. The local_ip
  needs to be routable from all hosts, but this is no different than
  before. There are more complex ways of dealing with this problem, but
  I think that this is the right fix and keeps it simple.

  I will be submitting a fix shortly via Gerrit.

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