Bug 1486344

My guess is global_physnet_mtu in neutron.conf isn't being used.  There is also path_mtu in the ML2.conf.  See:
https://docs.openstack.org/ocata/networking-guide/config-mtu.html

Looks like there is no support to configure that in OOO.  However there is support in puppet-neutron.  Can you try adding it as extraconfig and deploying again?
neutron::plugins::ml2::path_mtu

(In reply to Tim Rozet from comment #1)
> My guess is global_physnet_mtu in neutron.conf isn't being used.  There is
> also path_mtu in the ML2.conf.  See:
> https://docs.openstack.org/ocata/networking-guide/config-mtu.html
> 
> Looks like there is no support to configure that in OOO.  However there is
> support in puppet-neutron.  Can you try adding it as extraconfig and
> deploying again?
> neutron::plugins::ml2::path_mtu


I've reproduced the issue in my lab. 

I deployed a fresh install including extra config "neutron::plugins::ml2::path_mtu: 8996" in both controller and computes, "NeutronGlobalPhysnetMtu: 8996" and "mtu: 9000" in all interfaces (compute.yaml and controller.yaml) but I've found the same behavior.


There is a workaround while this BUG is fixed, you can use "ovs-vsctl set int br-int mtu_request=9000" command to set the br-int mtu (persistent across reboots), so it could be included using a post-script.

Thanks Luis.  Looks like this is not supported in ODL currently.

Yes, ODL will not configure br-int as mentioned with Luis's workaround.

Looks like the dhcp agent is responsible for setting the MTU in the VM instances for IPv4. ODL will need similar information to then configure the bridges.

Some options so far:
1. Enhancing networking-odl to pass that information.

2. Using hostconfig to pass it.

3. Use the other_config in Open_vSwitch table similar to how local_ip or provider_mappings is set. This looks closest to what the ml2 config is doing.

Seems the MTU is being passed by networking-odl as is to ODL itself, which does nothing with it.
This RFE is therefore for ODL.

2018-04-01 13:21:54.824 25 INFO networking_odl.journal.journal [req-56781fe2-4d22-42dc-9d5c-78c0be432124 - - - - -] Processing (Entry ID: 32) - create network d77b68d8-8e90-40e3-bcd6-8c9c65d60f83 (Time stamp: 63658185714.8)
2018-04-01 13:21:54.825 25 DEBUG networking_odl.common.client [req-56781fe2-4d22-42dc-9d5c-78c0be432124 - - - - -] Sending METHOD (post) URL (http://172.17.1.19:8081/controller/nb/v2/neutron/networks) JSON ({
  "network": {
    "provider:physical_network": "datacentre", 
    "ipv6_address_scope": null, 
    "revision_number": 5, 
    "port_security_enabled": true, 
    "provider:network_type": "flat", 
    "id": "d77b68d8-8e90-40e3-bcd6-8c9c65d60f83", 
    "router:external": true, 
    "availability_zone_hints": [], 
    "availability_zones": [], 
    "ipv4_address_scope": null, 
    "shared": false, 
    "project_id": "ba47b71f15f9457abc5ebccb62d29444", 
    "description": "", 
    "tags": [], 
    "updated_at": "2018-04-01T12:21:54Z", 
    "is_default": false, 
    "provider:segmentation_id": null, 
    "name": "public", 
    "admin_state_up": true, 
    "tenant_id": "ba47b71f15f9457abc5ebccb62d29444", 
    "created_at": "2018-04-01T12:21:54Z", 
    "mtu": 1500, 
    "vlan_transparent": null
  }

Mike that is the per-network MTU.  I think the 'global_physnet_mtu' is what we need passed to ODL.  It doesn't have to be passed by networking-odl, since it is a global value we can configure it via OOO and could come from an ODL config file.  The setting itself is already done in neutron.conf, so it would seem less redundant to just pass the configured value in Neutron to ODL:

https://github.com/openstack/neutron/blob/e81f4f68d0eb8def599f2addeac56656bd7f12b8/neutron/plugins/common/utils.py#L43

This should be fixed by https://bugzilla.redhat.com/show_bug.cgi?id=1553839 but it needs to be tested.

As per depreciation notice [1], closing this bug. Please reopen if relevant for RHOSP13, as this is the only version shipping ODL.

[1] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/14/html-single/release_notes/index#deprecated_functionality

As per depreciation notice [1], closing this bug. Please reopen if relevant for RHOSP13, as this is the only version shipping ODL.

[1] https://access.redhat.com/documentation/en-us/red_hat_openstack_platform/14/html-single/release_notes/index#deprecated_functionality