yahoo-eng-team team mailing list archive

[Jeroen van Bemmel <1859362@xxxxxxxxxxxxxxxxxx>]

Public bug reported:

Openstack allows the user to configure a different MTU per network, with
the default taken from the ML2 neutron::plugins::ml2::path_mtu value (
minus VXLAN overhead, if used )

(overcloud) [stack@vim1 ~]$ openstack network set --mtu 1500 management

However, currently (Queens at least) the user can specify arbitrary values
(overcloud) [stack@vim1 ~]$ openstack network set --mtu 99999 management
(overcloud) [stack@vim1 ~]$ openstack network set --mtu 10 management

The maximum possible MTU is 64K, but most network equipment won't support more than 9200-9300.
Even when using Jumbo frames and VXLAN encapsulation, practical deployments typically wouldn't use more than 9050 byte MTUs. RFC 791 requires a minimum MTU of 68, and IPv6 requires at least 1280

Proposal: Limit the accepted values to 1280-9250

** Affects: neutron
     Importance: Undecided
         Status: New


** Tags: mtu

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https://bugs.launchpad.net/bugs/1859362

Title:
  Neutron accepts arbitrary MTU values for networks

Status in neutron:
  New

Bug description:
  Openstack allows the user to configure a different MTU per network,
  with the default taken from the ML2 neutron::plugins::ml2::path_mtu
  value ( minus VXLAN overhead, if used )

  (overcloud) [stack@vim1 ~]$ openstack network set --mtu 1500
  management

  However, currently (Queens at least) the user can specify arbitrary values
  (overcloud) [stack@vim1 ~]$ openstack network set --mtu 99999 management
  (overcloud) [stack@vim1 ~]$ openstack network set --mtu 10 management

  The maximum possible MTU is 64K, but most network equipment won't support more than 9200-9300.
  Even when using Jumbo frames and VXLAN encapsulation, practical deployments typically wouldn't use more than 9050 byte MTUs. RFC 791 requires a minimum MTU of 68, and IPv6 requires at least 1280

  Proposal: Limit the accepted values to 1280-9250

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