Neutron - Networking Service

Preparation and deployment

Neutron is enabled by default in /etc/kolla/globals.yml:

#enable_neutron: "{{ enable_openstack_core | bool }}"

Network interfaces

Neutron external interface is used for communication with the external world, for example provider networks, routers and floating IPs. For setting up the neutron external interface modify /etc/kolla/globals.yml setting neutron_external_interface to the desired interface name. This interface is used by hosts in the network group. It is also used by hosts in the compute group if enable_neutron_provider_networks is set or DVR is enabled.

The interface is plugged into a bridge (Open vSwitch or Linux Bridge, depending on the driver) defined by neutron_bridge_name, which defaults to br-ex. The default Neutron physical network is physnet1.

Example: single interface

In the case where we have only a single Neutron external interface, configuration is simple:

neutron_external_interface: "eth1"

Example: multiple interfaces

In some cases it may be necessary to have multiple external network interfaces. This may be achieved via comma-separated lists:

neutron_external_interface: "eth1,eth2"
neutron_bridge_name: "br-ex1,br-ex2"

These two lists are “zipped” together, such that eth1 is plugged into the br-ex1 bridge, and eth2 is plugged into the br-ex2 bridge. Kolla Ansible maps these interfaces to Neutron physical networks physnet1 and physnet2 respectively.

Example: shared interface

Sometimes an interface used for Neutron external networking may also be used for other traffic. Plugging an interface directly into a bridge would prevent us from having a usable IP address on the interface. One solution to this issue is to use an intermediate Linux bridge and virtual Ethernet pair, then assign IP addresses on the Linux bridge. This setup is supported by Kayobe. It is out of scope here, as it is non-trivial to set up in a persistent manner.

Provider networks

Provider networks allow to connect compute instances directly to physical networks avoiding tunnels. This is necessary for example for some performance critical applications. Only administrators of OpenStack can create such networks.

To use provider networks in instances you also need to set the following in /etc/kolla/globals.yml:

enable_neutron_provider_networks: yes

For provider networks, compute hosts must have an external bridge created and configured by Ansible (this is also necessary when Neutron Distributed Virtual Routing (DVR) mode is enabled). In this case, ensure neutron_external_interface is configured correctly for hosts in the compute group.

OpenvSwitch (ml2/ovs)

By default kolla-ansible uses openvswitch as its underlying network mechanism, you can change that using the neutron_plugin_agent variable in /etc/kolla/globals.yml:

neutron_plugin_agent: "openvswitch"

When using Open vSwitch on a compatible kernel (4.3+ upstream, consult the documentation of your distribution for support details), you can switch to using the native OVS firewall driver by employing a configuration override (see OpenStack Service Configuration in Kolla). You can set it in /etc/kolla/config/neutron/openvswitch_agent.ini:

firewall_driver = openvswitch

L3 agent high availability

L3 and DHCP agents can be created in a high availability (HA) state with:

enable_neutron_agent_ha: "yes"

This allows networking to fail over across controllers if the active agent is stopped. If this option is enabled, it can be advantageous to also set:


Agents sometimes need to be restarted. This delay (in seconds) is invoked between the restart operations of each agent. When set properly, it will stop network outages caused by all agents restarting at the same time. The exact length of time it takes to restart is dependent on hardware and the number of routers present. A general rule of thumb is to set the value to 40 + 3n where n is the number of routers. For example, with 5 routers, 40 + (3 * 5) = 55 so the value could be set to 55. A much better approach however would be to first time how long an outage lasts, then set the value accordingly.

The default value is 0. A nonzero starting value would only result in outages if the failover time was greater than the delay, which would be more difficult to diagnose than consistent behaviour.

OVN (ml2/ovn)

In order to use OVN as mechanism driver for neutron, you need to set the following:

neutron_plugin_agent: "ovn"

When using OVN - Kolla Ansible will not enable distributed floating ip functionality (not enable external bridges on computes) by default. To change this behaviour you need to set the following:

neutron_ovn_distributed_fip: "yes"

Similarly - in order to have Neutron DHCP agents deployed in OVN networking scenario, use:

neutron_ovn_dhcp_agent: "yes"

This might be desired for example when Ironic bare metal nodes are used as a compute service. Currently OVN is not able to answer DHCP queries on port type external, this is where Neutron agent helps.

In order to deploy Neutron OVN Agent you need to set the following:

neutron_enable_ovn_agent: "yes"

Currently the agent is only needed for QoS for hardware offloaded ports.

Mellanox Infiniband (ml2/mlnx)

In order to add mlnx_infiniband to the list of mechanism driver for neutron to support Infiniband virtual funtions, you need to set the following (assuming neutron SR-IOV agent is also enabled using enable_neutron_sriov flag):

enable_neutron_mlnx: "yes"

Additionally, you will also need to provide physnet:interface mappings via neutron_mlnx_physnet_mappings which is presented to neutron_mlnx_agent container via mlnx_agent.ini and neutron_eswitchd container via eswitchd.conf:

  ibphysnet: "ib0"

SSH authentication in external systems (switches)

Kolla, by default, generates and copies an ssh key to the neutron_server container (under /var/lib/neutron/.ssh/id_rsa) which can be used for authentication in external systems (e.g. in networking-generic-switch or networking-ansible managed switches).

You can set neutron_ssh_key variable in passwords.yml to control the used key.

Custom Kernel Module Configuration for Neutron

Neutron may require specific kernel modules for certain functionalities. While there are predefined default modules in the Ansible role, users have the flexibility to add custom modules as needed.

To add custom kernel modules for Neutron, modify the configuration in /etc/kolla/globals.yml:

  - name: 'nf_conntrack_tftp'
    params: 'hashsize=4096'

In this example:

  • neutron_modules_extra: Allows users to specify additional modules and their associated parameters. The given configuration adjusts the hashsize parameter for the nf_conntrack_tftp module.