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Working with Neutron

OpenStack’s networking solution, Neutron, has representative elements for Contrail elements for Network (VirtualNetwork), Port (VirtualMachineInterface), Subnet (IpamSubnets), and Security-Group. The Neutron plugin translates the elements from one representation to another.

Data Structure

Although the actual data between Neutron and Contrail is similar, the listings of the elements differs significantly. In the Contrail API, the networking elements list is a summary, containing only the UUID, FQ name, and an href, however, in Neutron, all details of each resource are included in the list.

The Neutron plugin has an inefficient list retrieval operation, especially at scale, because it:

  • reads a list of resources (for example. GET /virtual-networks), then

  • iterates and reads in the details of the resource (GET /virtual-network/<uuid> ).

As a result, the API server spends most of the time in this type of GET operation just waiting for results from the Cassandra database.

The following features in Contrail improve performance with Neutron:

  • An optional detail query parameter is added in the GET of collections so that the API server returns details of all the resources in the list, instead of just a summary. This is accompanied by changes in the Contrail API library so that a caller gets returned a list of the objects.

  • The existing Contrail list API takes in an optional parent_id query parameter to return information about the resource anchored by the parent.

  • The Contrail API server reads objects from Cassandra in a multiget format into obj_uuid_cf, where object contents are stored, instead of reading in an xget/get format. This reduces the number of round-trips to and from the Cassandra database.

Network Sharing in Neutron

Using Neutron, a deployer can make a network accessible to other tenants or projects by using one of two attributes on a network:

  • Set the shared attribute to allow sharing.

  • Set the router:external attribute, when the plugin supports an external_net extension.

Using the Shared Attribute

When a network has the shared attribute set, users in other tenants or projects, including non-admin users, can access that network, using:

neutron net-list --shared

Users can also launch a virtual machine directly on that network, using:

nova boot <other-parameters> –nic net-id=<shared-net-id>

Using the Router:External Attribute

When a network has the router:external attribute set, users in other tenants or projects, including non-admin users, can use that network for allocating floating IPs, using:

neutron floatingip-create <router-external-net-id>

then associating the IP address pool with their instances.


The VN hosting the FIP pool should be marked shared and external.

Commands for Neutron Network Sharing

The following table summarizes the most common Neutron commands used with Contrail.

Table 1: Neutron commands



List all shared networks.

neutron net-list --shared

Create a network that has the shared attribute.

neutron net-create <net-name> –shared

Set the shared attribute on an existing network.

neutron net-update <net-name> -shared

List all router:external networks.

neutron net-list --router:external

Create a network that has the router:externalattribute.

neutron net-create <net-name> -router:external

Set the router:external attribute on an existing network.

neutron net-update <net-name> -router:external

Support for Neutron APIs

The OpenStack Neutron project provides virtual networking services among devices that are managed by the OpenStack compute service. Software developers create applications by using the OpenStack Networking API v2.0 (Neutron).

Contrail provides the following features to increase support for OpenStack Neutron:

  • Create a port independently of a virtual machine.

  • Support for more than one subnet on a virtual network.

  • Support for allocation pools on a subnet.

  • Per tenant quotas.

  • Enabling DHCP on a subnet.

  • External router can be used for floating IPs.

For more information about using OpenStack Networking API v2.0 (Neutron), refer to:​ and the OpenStack Neutron Wiki at:

Contrail Neutron Plugin

The Contrail Neutron plugin provides an implementation for the following core resources:

  • Network

  • Subnet

  • Port

It also implements the following standard and upstreamed Neutron extensions:

  • Security group

  • Router IP and floating IP

  • Per-tenant quota

  • Allowed address pair

The following Contrail-specific extensions are implemented:

  • Network IPAM

  • Network policy

  • VPC table and route table

  • Floating IP pools

The plugin does not implement native bulk, pagination, or sort operations and relies on emulation provided by the Neutron common code.

DHCP Options

In Neutron commands, DHCP options can be configured using extra-dhcp-options in port-create.


The opt_name and opt_value pairs that can be used are maintained in GitHub: .


In the Contrail architecture, the following are known incompatibilities with the Neutron API.

  • Filtering based on any arbitrary key in the resource is not supported. The only supported filtering is by id, name, and tenant_id.

  • To use a floating IP, it is not necessary to connect the public subnet and the private subnet to a Neutron router. Marking a public network with router:external is sufficient for a floating IP to be created and associated, and packet forwarding to it will work.

  • The default values for quotas are sourced from /etc/contrail/contrail-api.conf and not from /etc/neutron/neutron.conf.