Comment 5 for bug 1542108

Reviewed: https://review.openstack.org/283790
Committed: https://git.openstack.org/cgit/openstack/neutron/commit/?id=4df8d9a7016ab20fce235833d792b89309ec98a7
Submitter: Jenkins
Branch: master

commit 4df8d9a7016ab20fce235833d792b89309ec98a7
Author: Kevin Benton <email address hidden>
Date: Mon Feb 22 16:41:45 2016 -0800

    Make agent interface plugging utilize network MTU

    This changes the 'plug' and 'plug_new' interfaces of the
    LinuxInterfaceDriver to accept an MTU argument. It then
    updates the dhcp agent and l3 agent to pass the MTU that
    is set on the network that the port belongs to. This allows
    it to take into account the overhead calculations that are
    done for encapsulation types.

    It's necessary for the L3 agent to have the MTU because it
    must recognize when fragmentation is needed so it can fragment
    or generate an ICMP error.

    It's necessary for the DHCP agent to have the MTU so it doesn't
    interfere when it plugs into a bridge with a larger than 1500
    MTU (the bridge would reduce its MTU to match the agent).

    If an operator sets 'network_device_mtu', the value of that
    will be used instead to preserve previous behavior.

    Closes-Bug: #1549470
    Closes-Bug: #1542108
    Closes-Bug: #1542475
    DocImpact: Neutron agents now support arbitrary MTU
               configurations on each network (including
               jumbo frames). This is accomplished by checking
               the MTU value defined for each network on which
               it is wiring VIFs.
    Co-Authored-By: Matt Kassawara <email address hidden>
    Change-Id: Ic091fa78dfd133179c71cbc847bf955a06cb248a