yahoo-eng-team team mailing list archive

[Kevin Benton <1549408@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Neutron Network objects can have an 'MTU' field that specifies the MTU
that should be defined on all interfaces attached to that network.
However, Nova currently doesn't do anything with that information when
wiring up the Linux bridge and OVS ports. It only references the
network_device_mtu config option which is deprecated and doesn't take
into account the overhead of various encapsulation protocols.

So if network_device_mtu is not specified or is smaller than the MTU of
a Neutron network with jumbo frames, large packets from a VM will
silently be dropped on the Linux bridge due to the mismatch of MTUs
between the devices Nova has wired up and Neutron.

** Affects: nova
     Importance: Undecided
     Assignee: Kevin Benton (kevinbenton)
         Status: In Progress

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https://bugs.launchpad.net/bugs/1549408

Title:
  nova doesn't use Neutron MTUs when wiring up VIFs

Status in OpenStack Compute (nova):
  In Progress

Bug description:
  Neutron Network objects can have an 'MTU' field that specifies the MTU
  that should be defined on all interfaces attached to that network.
  However, Nova currently doesn't do anything with that information when
  wiring up the Linux bridge and OVS ports. It only references the
  network_device_mtu config option which is deprecated and doesn't take
  into account the overhead of various encapsulation protocols.

  So if network_device_mtu is not specified or is smaller than the MTU
  of a Neutron network with jumbo frames, large packets from a VM will
  silently be dropped on the Linux bridge due to the mismatch of MTUs
  between the devices Nova has wired up and Neutron.

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