openstack/neutron
Code Issues Proposed changes

ML2: Increase segment_mtu from 0 to 1500 bytes

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Neutron should return sane MTU values in the API. A Neutron Network
that has an MTU of zero wouldn't actually be a useful network, because
nothing could ever be transmitted. Zero is a junk value, so let's
replace it with standard ethernet MTU, which is a more believable value
to return to users.

Change-Id: I6a10c4dfc1f2198667f3d02528e2ca8020cb5bb8
Closes-Bug: #1549471
This commit is contained in:
Sean M. Collins
2016-02-24 16:00:12 -05:00
parent 3fb153b15b
commit b2d0985d05
2 changed files with 21 additions and 4 deletions
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8
neutron/plugins/ml2/config.py
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@@ -52,11 +52,11 @@ ml2_opts = [
'this feature and instances typically default to a '
'1500 MTU. Only impacts instances, not neutron network '
'components such as bridges and routers.')),
cfg.IntOpt('segment_mtu', default=0,
cfg.IntOpt('segment_mtu', default=1500,
help=_('The maximum permissible size of an unfragmented '
'packet travelling a L2 network segment. If <= 0, the '
'segment MTU is indeterminate and no calculation takes '
'place.')),
'packet travelling a L2 network segment. The default '
'value of 1500 is used as the segment MTU, to reflect '
'standard Ethernet.')),
cfg.ListOpt('physical_network_mtus',
default=[],
help=_("A list of mappings of physical networks to MTU "

17
releasenotes/notes/1500-default-segment-mtu-54e2cf6aea9602d5.yaml Normal file
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@@ -0,0 +1,17 @@
---
prelude: >
- The ML2 plug-in supports calculating the MTU for networks
that are realized as flat or VLAN networks, by consulting the
'segment_mtu' option. Prior to Mitaka, 'segment_mtu' defaults to 0 which
disables this feature. This creates slightly confusing API results when
querying Neutron networks, since the plugins that support the MTU API
extension would return networks with the MTU equal to zero. Networks
with an MTU of zero make little sense, since nothing could ever be transmitted.
In Mitaka, 'segment_mtu' now defaults to 1500 which is the standard MTU for Ethernet
networks in order to improve the "out of box" experience for typical deployments.
features:
- In Mitaka, queries to the Networking API for network objects will now
return network objects that contain a sane MTU value.
upgrade:
- Operators using the ML2 plug-in with existing data may need
to perform a database migration to update the MTU for existing networks