openstack/neutron
Code Issues Proposed changes

Make Neutron attempt to advertise MTUs by default

Browse Source 
It seems like a useful option, and it could be a more sane default,
rather than pushing the responsibility to enable this onto deployers and
provisioning tools[1]. In fact, it may be worth doing some more work to
take away some of the hassle of configuring all these things correctly,
and see if it can be automatically determined.

[1]: https://specs.openstack.org/openstack/fuel-specs/specs/7.0/jumbo-frames-between-instances.html

Related-Bug: #1527675
Change-Id: I5cbbc4660f8c4e15e59f8f5ce0419501bdd27348
This commit is contained in:
Sean M. Collins 2016-01-04 16:14:39 -08:00 committed by Ihar Hrachyshka
parent d6d43b32ca
commit 7e7d5dc861
2 changed files with 21 additions and 4 deletions
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9
neutron/common/config.py
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@ -153,10 +153,11 @@ core_opts = [
cfg.IntOpt('send_events_interval', default=2,
help=_('Number of seconds between sending events to nova if '
'there are any events to send.')),
cfg.BoolOpt('advertise_mtu', default=False,
help=_('If True, effort is made to advertise MTU settings '
'to VMs via network methods (DHCP and RA MTU options) '
'when the network\'s preferred MTU is known.')),
cfg.BoolOpt('advertise_mtu', default=True,
help=_('If True, advertise network MTU values if core plugin '
'calculates them. Currently, the only way to advertise '
'MTU to running instances is using corresponding DHCP '
'option.')),
cfg.StrOpt('ipam_driver',
help=_("Neutron IPAM (IP address management) driver to use. "
"If ipam_driver is not set (default behavior), no IPAM "

16
releasenotes/notes/advertise_mtu_by_default-d8b0b056a74517b8.yaml Normal file
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@ -0,0 +1,16 @@
---
features:
- By default, the DHCP agent provides a network MTU value to instances using
the corresponding DHCP option if core plugin calculates the value. For ML2
plugin, calculation mechanism is enabled by setting [ml2] path_mtu option
to a value greater than zero.
upgrade:
- To disable, use [DEFAULT] advertise_mtu = False.
other:
- For overlay networks managed by ML2 core plugin, the calculation algorithm
subtracts the overlay protocol overhead from the value of [ml2] path_mtu.
The DHCP agent provides the resulting (smaller) MTU to instances using
overlay networks.
- The [DEFAULT] advertise_mtu option must contain a consistent value on all
hosts running the DHCP agent.
- Typical networks can use [ml2] path_mtu = 1500.