DevStack Networking

An important part of the DevStack experience is networking that works by default for created guests. This might not be optimal for your particular testing environment, so this document tries its best to explain what’s going on.


If you don’t specify any configuration you will get the following:

  • neutron (including l3 with openvswitch)

  • private project networks for each openstack project

  • a floating ip range of with the gateway of

  • the demo project configured with fixed ips on a subnet allocated from the range

  • a br-ex interface controlled by neutron for all its networking (this is not connected to any physical interfaces).

  • DNS resolution for guests based on the resolv.conf for your host

  • an ip masq rule that allows created guests to route out

This creates an environment which is isolated to the single host. Guests can get to the external network for package updates. Tempest tests will work in this environment.


By default all OpenStack environments have security group rules which block all inbound packets to guests. If you want to be able to ssh / ping your created guests you should run the following.

openstack security group rule create --proto icmp --dst-port 0 default
openstack security group rule create --proto tcp --dst-port 22 default

Locally Accessible Guests

If you want to make your guests accessible from other machines on your network, we have to connect br-ex to a physical interface.

Dedicated Guest Interface

If you have 2 or more interfaces on your devstack server, you can allocate an interface to neutron to fully manage. This should not be the same interface you use to ssh into the devstack server itself.

This is done by setting with the PUBLIC_INTERFACE attribute.


That will put all layer 2 traffic from your guests onto the main network. When running in this mode the ip masq rule is not added in your devstack, you are responsible for making routing work on your local network.

Shared Guest Interface


This is not a recommended configuration. Because of interactions between ovs and bridging, if you reboot your box with active networking you may lose network connectivity to your system.

If you need your guests accessible on the network, but only have 1 interface (using something like a NUC), you can share your one network. But in order for this to work you need to manually set a lot of addresses, and have them all exactly correct.


In order for this scenario to work the floating ip network must match the default networking on your server. This breaks HOST_IP detection, as we exclude the floating range by default, so you have to specify that manually.

The PUBLIC_NETWORK_GATEWAY is the gateway that server would normally use to get off the network. Q_FLOATING_ALLOCATION_POOL controls the range of floating ips that will be handed out. As we are sharing your existing network, you’ll want to give it a slice that your local dhcp server is not allocating. Otherwise you could easily have conflicting ip addresses, and cause havoc with your local network.

Private Network Addressing

The private networks addresses are controlled by the IPV4_ADDRS_SAFE_TO_USE and the IPV6_ADDRS_SAFE_TO_USE variables. This allows users to specify one single variable of safe internal IPs to use that will be referenced whether or not subnetpools are in use.

For IPv4, FIXED_RANGE and SUBNETPOOL_PREFIX_V4 will just default to the value of IPV4_ADDRS_SAFE_TO_USE directly.

For IPv6, FIXED_RANGE_V6 will default to the first /64 of the value of IPV6_ADDRS_SAFE_TO_USE. If IPV6_ADDRS_SAFE_TO_USE is /64 or smaller, FIXED_RANGE_V6 will just use the value of that directly. SUBNETPOOL_PREFIX_V6 will just default to the value of IPV6_ADDRS_SAFE_TO_USE directly.