=====================
 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.

Defaults
========

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 172.24.4.0/24 with the gateway of 172.24.4.1
* the demo project configured with fixed ips on a subnet allocated from
  the 10.0.0.0/22 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.

.. note::

   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.

   .. code-block:: bash

      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 you 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.

.. code-block:: bash

   [[local|localrc]]
   PUBLIC_INTERFACE=eth1

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
----------------------

.. warning::

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

.. code-block:: bash

   [[local|localrc]]
   PUBLIC_INTERFACE=eth0
   HOST_IP=10.42.0.52
   FLOATING_RANGE=10.42.0.52/24
   PUBLIC_NETWORK_GATEWAY=10.42.0.1
   Q_FLOATING_ALLOCATION_POOL=start=10.42.0.250,end=10.42.0.254

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.