Adventures in OpenStack – Neutron Setup Errata and Multiple External Networks

So, a bit of a confession. The article Adventures in OpenStack – Networking has a an issue in how to set up external networks. The section that mentioned what to enter in the [ovs] section actually does nothing.

Why? Because by default, the Layer 3 (L3) agent only allows one external network, hardcoded in the config and defaulted to br-ex:

# Name of bridge used for external network traffic. This should be set to
# empty value for the linux bridge. when this parameter is set, each L3 agent
# can be associated with no more than one external network.
# external_network_bridge = br-ex

As such, the first network flagged as “external”, as long as the name is available as a valid network name in the ML2 plugin config, will function and be mapped to the external bridge listed above.

This came up for me when I tried to add a second external network. Before a few versions of OpenStack ago, this needed to be done by running a second Layer 3 agent. But now with the ML2 plugin it is possible to run them out of the same agent.

The right way to do this is:

  • Make sure that have all the external networks listed in the ML2 config. If this is the flat network type, it would look like so:
[ml2_type_flat]
flat_networks = external,external2
  • Then, head over to l3_agent.ini and ensure that you have cleared the following as blank: 1) the external gateway ID, and the external network bridge name:
gateway_external_network_id =
external_network_bridge =

I make sure these are explicitly defined (uncommented and set correctly), to avoid issues.

  • Finally, add the OVS bits to the right config which should be in /etc/neutron/plugins/openvswitch/ovs_neutron_plugin.ini:
network_vlan_ranges = external,external2
bridge_mappings = external:br-ex,external2:br-ex2

Even though network_vlan_ranges might seem redundant or misleading for flat networks, the definition is still required.

You are now ready to restart Neutron. There is a shortcut for this, by the way:

openstack-service restart neutron

One Last Thing

If you are having issues with your existing external networks after performing the above, check for this in your Neutron logs:

openvswitch-agent.log:2015-02-22 18:27:39.369 22377 WARNING neutron.plugins.openvswitch.agent.ovs_neutron_agent [req-2fb3e41a-f068-4737-97f8-580af5ddad27 None] Device 598f6434-06ff-4280-af5c-6ce7c312ca5b not defined on plugin
server.log:2015-02-22 18:27:37.393 22455 WARNING neutron.plugins.ml2.rpc [req-2fb3e41a-f068-4737-97f8-580af5ddad27 None] Device 598f6434-06ff-4280-af5c-6ce7c312ca5b requested by agent ovs-agent-beefhost.vcts.local on network d8f7930b-d4e9-422d-b789-7c2866ab81e8 not bound, vif_type: binding_failed

If you see this, you may need to re-create your external networks. There may be another way to fix this, seeing as it may have to do with a bad external network/bridge association, but if you are in a (small enough) lab, it should be trivial to just tear down and rebuild the network and router gateway bindings (only the external networks, subnets, and gateway associations need to be fixed).

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