Juju Charm - Neutron Gateway
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The neutron-gateway charm deploys the data plane of Neutron, the core OpenStack service that provides software defined networking (SDN) for Nova instances. This provides the Neutron Gateway service, which in turn supplies two key services: L3 network routing and DHCP. The charm works alongside other Juju-deployed OpenStack applications; in particular: neutron-openvswitch, nova-compute, and nova-cloud-controller.

Note: Starting with OpenStack Train, the neutron-gateway and neutron-openvswitch charm combination can be replaced by the OVN charms (e.g. ovn-central, ovn-chassis, and neutron-api-plugin-ovn).



This section covers common and/or important configuration options. See file config.yaml for the full list of options, along with their descriptions and default values. See the Juju documentation for details on configuring applications.


A bridge that Neutron Gateway will bind to, given in the form of a space-delimited bridge:port mapping (e.g. 'br-ex:ens8'). The port will be added to its corresponding bridge.

Note: If network device names are not consistent between hosts (e.g. 'eth1' and 'ens8') a list of values can be provided where a MAC address is used in the place of a device name. The charm will iterate through the list and configure the first matching interface.

The specified bridge(s) should match the one(s) defined in the bridge-mappings option.

Flat or VLAN network types are supported.

The device itself must not have any L3 configuration. In MAAS, it must have an IP mode of 'Unconfigured'.


A space-delimited list of ML2 data provider:bridge mappings (e.g. 'physnet1:br-ex'). The specified bridge(s) should match the one(s) defined in the data-port option.


The openstack-origin option states the software sources. A common value is an OpenStack UCA release (e.g. 'cloud:bionic-ussuri' or 'cloud:focal-victoria'). See Ubuntu Cloud Archive. The underlying host's existing apt sources will be used if this option is not specified (this behaviour can be explicitly chosen by using the value of 'distro').


These deployment instructions assume the following pre-existing applications: neutron-api, nova-cloud-controller, and rabbitmq-server.

Important: For Neutron Gateway to function properly, the nova-cloud-controller charm must have its network-manager option set to 'Neutron'.

Deploy Neutron Gateway:

juju deploy neutron-gateway
juju add-relation neutron-gateway:quantum-network-service nova-cloud-controller:quantum-network-service
juju add-relation neutron-gateway:neutron-plugin-api neutron-api:neutron-plugin-api
juju add-relation neutron-gateway:amqp rabbitmq-server:amqp

Port configuration

Network ports are configured with the bridge-mappings and data-port options but the neutron-api charm also has several relevant options (e.g. flat-network-providers, vlan-ranges, etc.). Additionally, the network topology can be further defined with supplementary openstack client commands.

Example 1
This configuration has a single external network and is typically used when floating IP addresses are combined with a GRE private network.

Charm option values (YAML):

    bridge-mappings: physnet1:br-ex
    data-port: br-ex:eth1
    flat-network-providers: physnet1

Supplementary commands:

openstack network create --provider-network-type flat \
   --provider-physical-network physnet1 --external \
openstack router set router1 --external-gateway external

Example 2
This configuration is for two networks, where an internal private network is directly connected to the gateway with public IP addresses but a floating IP address range is also offered.

Charm option values (YAML):

    bridge-mappings: physnet1:br-data external:br-ex
    data-port: br-data:eth1 br-ex:eth2
    flat-network-providers: physnet1 external

Example 3
This configuration has two external networks, where one is for public instance addresses and one is for floating IP addresses. Both networks are on the same physical network connection (but they might be on different VLANs).

Charm option values (YAML):

    bridge-mappings: physnet1:br-data
    data-port: br-data:eth1
    flat-network-providers: physnet1

Supplementary commands:

openstack network create --provider-network-type vlan \
   --provider-segment 400 \
   --provider-physical-network physnet1 --share \
openstack network create --provider-network-type vlan \
   --provider-segment 401 \
   --provider-physical-network physnet1 --share --external \
openstack router set router1 --external-gateway floating

legacy ext-port option

The ext-port option is deprecated and is superseded by the data-port option. The ext-port option always created a bridge called 'br-ex' for external networks that was used implicitly by external router interfaces.

The following will occur if both the data-port and ext-port options are set:

  • the neutron-gateway unit will be marked as 'blocked' to indicate that the charm is misconfigured
  • the ext-port option will be ignored
  • a warning will be logged

Instance MTU

When using Open vSwitch plugin with GRE tunnels the default MTU of 1500 can cause packet fragmentation due to GRE overhead. One solution to this problem is to increase the MTU on physical hosts and network equipment. When this is not feasible the charm's instance-mtu option can be used to reduce instance MTU via DHCP:

juju config neutron-gateway instance-mtu=1400

Note: The instance-mtu option is supported starting with OpenStack Havana.


This section covers Juju actions supported by the charm. Actions allow specific operations to be performed on a per-unit basis. To display action descriptions run juju actions --schema neutron-gateway. If the charm is not deployed then see file actions.yaml.

  • cleanup
  • get-status-dhcp
  • get-status-lb
  • get-status-routers
  • openstack-upgrade
  • pause
  • restart-services
  • resume
  • restart-services
  • run-deferred-hooks
  • security-checklist
  • show-deferred-events

Deferred service events

Operational or maintenance procedures applied to a cloud often lead to the restarting of various OpenStack services and/or the calling of certain charm hooks. Although normal, such events can be undesirable due to the service interruptions they can cause.

The deferred service events feature provides the operator the choice of preventing these service restarts and hook calls from occurring, which can then be resolved at a more opportune time.

See the Deferred service events page in the OpenStack Charms Deployment Guide for an in-depth treatment of this feature.


The OpenStack Charms project maintains two documentation guides:


Please report bugs on Launchpad.