Neutron-Neutron Interconnections

Neutron-Neutron Interconnections

Launchpad RFE:

Problem Description

Today, to realize connectivity between two OpenStack clouds or more (e.g. between distinct OpenStack deployments, or between OpenStack regions, for instance) some options are available, such as floating IPs, VPNaaS (IPSec-based), and BGPVPNs.

However, none of these options are appropriate to address use cases where all the following properties are desired:

  1. interconnection consumable on-demand, without admin intervention [1]
  2. have network isolation and allow the use of private IP addressing end-to-end [2]
  3. avoid the overhead of packet encryption [3]

An additional design requirement to the solution is to avoid introducing a component that would require having admin rights on all the OpenStack clouds involved.

The goal of this spec is a solution to provide network connectivity between two or more OpenStack deployments or regions, respecting these requirements.

Use cases

Example 1

User Foo has credentials for OpenStack cloud A and OpenStack cloud B, one Router X in OpenStack A, one Router Y in OpenStack B, both using a distinct subnet in the private IPv4 address space.

User Foo would like to consume via an API a service that will result in establishing IP connectivity between Router A and Router B.

Example 2

Same as example 1, but this time L2 connectivity is desired between Network X in OpenStack A, and Network Y in OpenStack B.

Example 3

Same as example 1 or 2, but with 3 OpenStack deployments involved.

Proposed Change


The proposition consists in introducing a service plugin and a corresponding API extension involving a new ‘interconnection’ resource. The ‘interconnection’ resource on a Neutron instance will refer to both a local resource (e.g. Router A) and a remote resource (OpenStack B:Router B), and will have the semantic that connectivity is desired between the two.

This resource will be part of two sorts of API calls:

  1. calls between the user having the connectivity need and each Neutron instance involved; the role of these calls is to let the need for connectivity be known by all Neutron instances
  2. API calls between a Neutron instance and another Neutron instance; the role of these calls is to:
    • let each Neutron instance validate the consistency between the “interconnection” resources defined locally and the “interconnection” resources made in other Neutron instances
    • after this validation, let two Neutron instances identify the mechanism to use and the per-interconnection parameters (depending on the mechanism; could be a pair of VLANs on a interconnection box, a BGPVPN RT identifiers, VXLAN ids, etc.)
                               | tenant user |
                                    |   |
   .--------------------------------'   '--------------------.
   | A1. create "interconnection"                            |
   |     between local net X,                                |
   |     and "Neutron B: net Y"                              |
   |                                          A2. create "interconnection"
   |                                              between local net Y,
   |                                              and "Neutron A: net X"
   |                                                         |
   |                                                         |
   |                                                         |
   |                                                         |
   V                         B1. check symmetric inter.      V
.-------------------------.                      (fail) .--------------------.
|                         +---------------------------> |                    |
|   Neutron A             |                             |   Neutron B        |
|                         | <---------------------------+                    |
|                         |  B2. check symmetric inter. |                    |
|                         |                       (ok!) |                    |
|                         |                             |                    |
|                         +---------------------------> |                    |
|                         | <---------------------------+                    |
'-------------------------'  B3. exchange info to build '--------------------'
                   net X        interconnection           net Y
                     |                                      |
                     |                                      |
                   --+                                      +--
                     |      C. interconnection is built     |
                     +--    - - - - - - - - - - - - - -   --+
                     |                                      |
                     |                                      |

Note that the order between A1/A2/B1/B2 can vary, but the result is unchanged: at least one of the two Neutron instances will eventually confirm that the interconnection has been defined on both side symmetrically, and the interconnection setup phase will ultimately proceed on both sides (see Details on operations).

When more than two OpenStack deployments, or more than two OpenStack regions, are involved, these API calls will happen for each pair of region/deployments.

Base assumptions, trust model

The base assumption underlying the trust model in this proposal is that the end user requesting connectivity delegates trust to each OpenStack deployment to provide only the interconnection requested, i.e. to not create connectivity between resources unless requested.

To respect this contract each OpenStack deployment needs, by definition, a trust relationship with the other(s) OpenStack deployment(s) involved in these interconnections; practically speaking it cannot do better, when receiving a packet from another deployment, identified as intended for own of its local network A (VLAN, VXLAN ID, MPLS label, etc.) to trust that this identifier was pushed by the OpenStack deployment by mechanisms ultimately respecting the contract of these specifications.

Another aspect, obvious but better made explicit, is that the choice and definition of the network identifiers that will be used for an interconnection and to keep interconnections isolated from one another, are not controlled by consumers of this API. In this proposal these consumers do not and cannot write, or even read, these identifiers.

Note that only the API calls to the ‘interconnection’ resources at steps A1/A2 require write access to the “interconnection” resources by tenant users (but not to the attributes related to the network mechanism to use).

The calls at steps B1/B2, only require read-only access to these resources; this can be achieved by introducing an “interconnection” role with read-only access to all “interconnection” resources, and having each OpenStack deployment having credentials for a user with this role in other OpenStack deployments.

With the above in mind, Keystone federation is not required for the calls at steps A1/A2, nor for the calls at step B1/B2. However, using Keystone Federation for the user(s) used at step B1/B2 will certainly be useful and will avoid requiring the management in each Neutron instance of the credentials to use to each other OpenStack.

Interconnection mechanisms

Although these specifications try to be agnostic to the network technique ultimately used to realize an interconnection, the assumption is made that for each ‘interconnection’, there is a technique common to the two OpenStack deployments involved.

The approach proposed is a simple approach where each OpenStack deployment determines based on a configuration file, which technique to use when establishing an interconnection with a given OpenStack deployment.

Note that only the parameters that do not differ between two interconnection would sit in a configuration file. The API exchange between two Neutron instances is used to exchange parameters that are specific to each interconnection.

Example interconnection techniques

The following techniques can be considered for realizing interconnections:

  • BGP-based VPNs: already supported via the Neutron BGPVPN Interconnection service (see networking-bgpvpn), it allows to create L2 (with EVPN) or L3 connectivity (with BGP/MPLS IP VPNs)
  • VXLAN stitching with networking-l2gw (details remain to be investigated)
  • VLAN stitching (details remain to be investigated)

It is expected that the first implementation will provide at least support for the BGPVPN interconnection technique, which is already supported across an interesting range of Neutron backends (Neutron reference drivers, OpenDaylight, OpenContrail, Nuage Networks), and hence would allow this API extension to be implemented on day one with a support for all these controllers without any further per-controller driver development.

Details on operations

When an “interconnection” resource is created, the Neutron instance will check that the symmetric interconnection exists on the remote Neutron instance designated in the interconnection, and will not proceed further until this becomes true.

This check is what establishes the end-to-end trust, that on both sides the connectivity has been requested.

Once a Neutron instance determines that an interconnection is symmetrically defined, further exchanges happen to determine the network parameters to use to realize the interconnection:

  • the Neutron (e.g. Neutron B) that just confirmed the symmetricity allocates the required network identifiers, and asks the remote Neutron instance (A) to refresh its state
  • Neutron A refreshes its state: checks symmetricity again (which now succeeds) retrieves at the same time the network identifiers allocated by B, and asks Neutron B to refresh
  • Neutron B refreshes again, this time retrieves at the same time the network identifiers allocated by A

In the above, “ask the remote Neutron instance to refresh its state” is done with a PUT on a specific refresh action on the interconnection.

Interconnection lifecycle

In the previous section, it is implicit that an interconnection is along its life in different states before it is ultimately realized. When an interconnection resource is deleted on one side, the other side need also to ultimately be able to update its own state (if only for cleanup purpose or giving proper feedback to end users).

Additionally, the interaction between a Neutron instance with another Neutron instance needs to happen out of the API call processing path, because it is not desirable that the success of a local API call would depend on the success of an operation with an external component which possibly would not be available at the moment.

For all these reasons, a state machine will be introduced to handle the lifecycle of an interconnection resource, with triggered and periodic operation being done out-of-band of the API calls, to handle the operations for each state.

Exposing this state in the API will allow:

  • end users to have feedback on how close they are to having something working
  • each Neutron instance to possibly identify that the remote state is inconsistent with the local state

State machine summary:

interconnection resource has been created, but the existence of the symmetric interconnection hasn’t been validated yet
the existence of the symmetric interconnection has been validated
local interconnection parameters have been defined (remote parameters are still unknown)
both local parameters and remote parameters are known, interconnection is being built
interconnection has been setup, it should work
local action taken to delete this interconnection, action is being taken to have the remote state get in sync
implicit state corresponding to the resource not existing anymore


The proposal is to introduce an API extension inter, with a new interconnection resource.

Interconnection resource

The new interconnection API resource will be introduce under the inter API prefix, and having the following attributes:

Attribute Name Type Access Comment
id uuid RO  
project_id uuid RO  
type enum RO router, network_l2, network_l3
state enum RO will be updated by Neutron along the life of the resource see states in Interconnection lifecycle
name string RW  
local_resource_id uuid RO router or network UUID
remote_resource_id uuid RO router or network UUID
remote_keystone string RO AUTH_URL of remote keystone
remote_region string RO region in remote keystone
local_parameters dict


will be updated by Neutron along the life of the resource

remote_parameters dict

This resource will be used with typical CRUD operations:

  • POST /v2.0/inter/interconnections
  • GET /v2.0/inter/interconnections
  • GET /v2.0/inter/interconnections/<uuid>
  • PUT /v2.0/inter/interconnections/<uuid>
  • DELETE /v2.0/inter/interconnections/<uuid>

Additionally, an additional REST operation is introduced to trigger a refresh action on an interconnection resource:

  • PUT /v2.0/inter/interconnections/<uuid>/refresh

When this action is triggered the neutron instance on which the call is made will try to retrieve (GET) an interconnection resource on the remote neutron instance having same type as the local resource, as local_resource_id the local resource remote_resource_id, and as remote_resource_id the local resource local_resource_id. Depending on the current local state, and depending on success or failure to find such a resource, the local state machine will transition.


This shows an example of API exchanges for a Neutron-Neutron interconnection between two Networks.

API Call A1, from tenant user to Neutron A:

POST /v2.0/inter/interconnections
         'type': 'network'
         'local_resource_id': <uuid of network X>
         'remote_keystone': "http//<keystone-B>/identity",
         'remote_region': 'RegionOne',
         'remote_resource_id': <uuid of network Y>

Response: 200 OK

{'interconnection': {
     'id': <uuid 1>

API Call B1, from Neutron A to Neutron B:

GET /v2.0/inter/interconnections?local_resource_id=<uuid of network Y>&remote_resource_id=<uuid of network X>

Response: 404

API Call A2, from tenant user to Neutron B:

POST /v2.0/inter/interconnections
         'type': 'network'
         'local_resource_id': <uuid of network Y>
         'remote_keystone': "http//<keystone-A>/identity",
         'remote_region': 'RegionOne',
         'remote_resource_id': <uuid of network X>

Response: 200 OK

{'interconnection': {
     'id': <uuid 2>

API Call B2, from Neutron B to Neutron A:

GET /v2.0/inter/interconnections/local_resource_id=<uuid of network X>&remote_resource_id=<uuid of network Y>

Response: 200 OK

{'interconnection': {
     'id': <uuid 1>
     'local_parameters": {}

API Call B3’ from Neutron B to Neutron A:

PUT /v2.0/inter/interconnections/<uuid 1>/refresh

{'interconnection': {
     'id': <uuid 2>
     'local_parameters": {}

Response: 200 OK

API Call B3’‘, from Neutron A to Neutron B

PUT /v2.0/inter/interconnections/<uuid 2>/refresh

Response: 200 OK

{'interconnection': {
     'id': <uuid 2>
     'local_parameters": {
         'foo': '42'

API Call B3’‘’, from Neutron B to Neutron A

PUT /v2.0/inter/interconnections/<uuid 1>/refresh

Response: 200 OK

{'interconnection': {
     'id': <uuid 1>
     'remote_parameters': {
         'foo': '42'
     'local_parameters": {
         'bar': '43'

Command Line Client Impact

python-neutronclient will be updated to introduce an OSC extension to create/remove/update/delete interconnection resources.

Client Libraries Impact

python-neutronclient and openstacksdk will need to be updated to support create/remove/update/delete operations on interconnection resources.


Przemyslaw Jasek contributed to exploring ideas that lead to this proposal during a six-months internship at Orange.


[1]possible with floating IPs, VPNaaS, but not with the BGP VPN interconnections API extension (using a BGPVPN does not require admin right, but creating a new BGPVPN does require admin rights)
[2]possible with VPNaaS, and BGP VPN interconnections, but not with floating IPs
[3]possible with floating IPs and BGP VPN interconnections, but by definition not with VPNaaS
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