Routed provider networks¶

Note

Experimental feature. Use of this feature requires the OpenStack client version 3.3 or newer.

Before routed provider networks, the Networking service could not present a multi-segment layer-3 network as a single entity. Thus, each operator typically chose one of the following architectures:

Single large layer-2 network
Multiple smaller layer-2 networks

Single large layer-2 networks become complex at scale and involve significant failure domains.

Multiple smaller layer-2 networks scale better and shrink failure domains, but leave network selection to the user. Without additional information, users cannot easily differentiate these networks.

A routed provider network enables a single provider network to represent multiple layer-2 networks (broadcast domains) or segments and enables the operator to present one network to users. However, the particular IP addresses available to an instance depend on the segment of the network available on the particular compute node.

Similar to conventional networking, layer-2 (switching) handles transit of traffic between ports on the same segment and layer-3 (routing) handles transit of traffic between segments.

Each segment requires at least one subnet that explicitly belongs to that segment. The association between a segment and a subnet distinguishes a routed provider network from other types of networks. The Networking service enforces that either zero or all subnets on a particular network associate with a segment. For example, attempting to create a subnet without a segment on a network containing subnets with segments generates an error.

The Networking service does not provide layer-3 services between segments. Instead, it relies on physical network infrastructure to route subnets. Thus, both the Networking service and physical network infrastructure must contain configuration for routed provider networks, similar to conventional provider networks. In the future, implementation of dynamic routing protocols may ease configuration of routed networks.

Limitations¶

The Newton implementation contains the following limitations:

The Compute scheduler lacks awareness of IP address resources on a routed network. Thus, the scheduler could exhaust the IP addresses in one segment before assigning IP addresses from another segment. The Ocata release of the Compute scheduler should provide the capability of scheduling around segments without available IP addresses. In Newton, the Compute scheduler selects any compute node on the provider network. If the segment on that compute node lacks available IP addresses, port binding fails and the Compute scheduler chooses another compute node without regard to segments. Rescheduling continues up to the maximum number of retries. Operators should monitor IP usage and add subnets to segments prior to exhaustion of IP addresses. For more information, see the blueprint.
A routed provider network cannot also function as a router:external networks which prevents compatibility with floating IPv4 addresses. Additional routing, possibly using BGP dynamic routing, could address this issue in the future.

Prerequisites¶

Routed provider networks require additional prerequisites over conventional provider networks. We recommend using the following procedure:

Begin with segments. The Networking service defines a segment using the following components:
- Unique physical network name
- Segmentation type
- Segmentation ID
For example, provider1, VLAN, and 2016. See the API reference for more information.

Within a network, use a unique physical network name for each segment which enables reuse of the same segmentation details between subnets. For example, using the same VLAN ID across all segments of a particular provider network. Similar to conventional provider networks, the operator must provision the layer-2 physical network infrastructure accordingly.

Implement routing between segments.

The Networking service does not provision routing among segments. The operator must implement routing among segments of a provider network. Each subnet on a segment must contain the gateway address of the router interface on that particular subnet. For example:

Segment	Version	Addresses	Gateway
segment1	4	203.0.113.0/24	203.0.113.1
segment1	6	fd00:203:0:113::/64	fd00:203:0:113::1
segment2	4	198.51.100.0/24	198.51.100.1
segment2	6	fd00:198:51:100::/64	fd00:198:51:100::1

Map segments to compute nodes.

Routed provider networks imply that compute nodes reside on different segments. The operator must ensure that every compute host that is supposed to participate in a router provider network has direct connectivity to one of its segments.

Host	Rack	Physical Network
compute0001	rack 1	segment 1
compute0002	rack 1	segment 1
...	...	...
compute0101	rack 2	segment 2
compute0102	rack 2	segment 2
compute0102	rack 2	segment 2
...	...	...

Deploy DHCP agents.

Unlike conventional provider networks, a DHCP agent cannot support more than one segment within a network. The operator must deploy at least one DHCP agent per segment. Consider deploying DHCP agents on compute nodes containing the segments rather than one or more network nodes to reduce node count.

Host Rack Physical Network

network0001 rack 1 segment 1

network0002 rack 2 segment 2

... ... ...
Configure communication of the Networking service with the Compute scheduler.

An instance with an interface with an IPv4 address in a routed provider network must be placed by the Compute scheduler in a host that has access to a segment with available IPv4 addresses. To make this possible, the Networking service communicates to the Compute scheduler the inventory of IPv4 addresses associated with each segment of a routed provider network. The operator must configure the authentication credentials that the Networking service will use to communicate with the Compute scheduler’s placement API. Please see below an example configuration.

Note

Coordination between the Networking service and the Compute scheduler is not necessary for IPv6 subnets as a consequence of their large address spaces.
Note

The coordination between the Networking service and the Compute scheduler requires the following minimum API micro-versions.
- Compute service API: 2.41
- Placement API: 1.1

Example configuration¶

Controller node¶

Enable the segments service plug-in by appending segments to the list of service_plugins in the neutron.conf file on all nodes running the neutron-server service:
```
[DEFAULT]
# ...
service_plugins = ..., segments
```

Add a placement section to the neutron.conf file with authentication credentials for the Compute service placement API:

[placement]
auth_uri = http://192.0.2.72/identity
project_domain_name = Default
project_name = service
user_domain_name = Default
password = apassword
username = nova
auth_url = http://192.0.2.72/identity_admin
auth_type = password
region_name = RegionOne

Restart the neutron-server service.

Network or compute nodes¶

Configure the layer-2 agent on each node to map one or more segments to the appropriate physical network bridge or interface and restart the agent.

Create a routed provider network¶

The following steps create a routed provider network with two segments. Each segment contains one IPv4 subnet and one IPv6 subnet.

Source the administrative project credentials.

Create a VLAN provider network which includes a default segment. In this example, the network uses the provider1 physical network with VLAN ID 2016.

$ openstack network create --share --provider-physical-network provider1 \
  --provider-network-type vlan --provider-segment 2016 multisegment1
+---------------------------+--------------------------------------+
| Field                     | Value                                |
+---------------------------+--------------------------------------+
| admin_state_up            | UP                                   |
| id                        | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 |
| ipv4_address_scope        | None                                 |
| ipv6_address_scope        | None                                 |
| l2_adjacency              | True                                 |
| mtu                       | 1500                                 |
| name                      | multisegment1                        |
| port_security_enabled     | True                                 |
| provider:network_type     | vlan                                 |
| provider:physical_network | provider1                            |
| provider:segmentation_id  | 2016                                 |
| router:external           | Internal                             |
| shared                    | True                                 |
| status                    | ACTIVE                               |
| subnets                   |                                      |
| tags                      | []                                   |
+---------------------------+--------------------------------------+

Rename the default segment to segment1.

$ openstack network segment list --network multisegment1
+--------------------------------------+----------+--------------------------------------+--------------+---------+
| ID                                   | Name     | Network                              | Network Type | Segment |
+--------------------------------------+----------+--------------------------------------+--------------+---------+
| 43e16869-ad31-48e4-87ce-acf756709e18 | None     | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 | vlan         |    2016 |
+--------------------------------------+----------+--------------------------------------+--------------+---------+

$ openstack network segment set --name segment1 43e16869-ad31-48e4-87ce-acf756709e18

Note

This command provides no output.

Create a second segment on the provider network. In this example, the segment uses the provider2 physical network with VLAN ID 2016.

$ openstack network segment create --physical-network provider2 \
   --network-type vlan --segment 2016 --network multisegment1 segment2
+------------------+--------------------------------------+
| Field            | Value                                |
+------------------+--------------------------------------+
| description      | None                                 |
| headers          |                                      |
| id               | 053b7925-9a89-4489-9992-e164c8cc8763 |
| name             | segment2                             |
| network_id       | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 |
| network_type     | vlan                                 |
| physical_network | provider2                            |
| segmentation_id  | 2016                                 |
+------------------+--------------------------------------+

Verify that the network contains the segment1 and segment2 segments.

$ openstack network segment list --network multisegment1
+--------------------------------------+----------+--------------------------------------+--------------+---------+
| ID                                   | Name     | Network                              | Network Type | Segment |
+--------------------------------------+----------+--------------------------------------+--------------+---------+
| 053b7925-9a89-4489-9992-e164c8cc8763 | segment2 | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 | vlan         |    2016 |
| 43e16869-ad31-48e4-87ce-acf756709e18 | segment1 | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 | vlan         |    2016 |
+--------------------------------------+----------+--------------------------------------+--------------+---------+

Create subnets on the segment1 segment. In this example, the IPv4 subnet uses 203.0.113.0/24 and the IPv6 subnet uses fd00:203:0:113::/64.

$ openstack subnet create \
  --network multisegment1 --network-segment segment1 \
  --ip-version 4 --subnet-range 203.0.113.0/24 \
  multisegment1-segment1-v4
+-------------------+--------------------------------------+
| Field             | Value                                |
+-------------------+--------------------------------------+
| allocation_pools  | 203.0.113.2-203.0.113.254            |
| cidr              | 203.0.113.0/24                       |
| enable_dhcp       | True                                 |
| gateway_ip        | 203.0.113.1                          |
| id                | c428797a-6f8e-4cb1-b394-c404318a2762 |
| ip_version        | 4                                    |
| name              | multisegment1-segment1-v4            |
| network_id        | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 |
| segment_id        | 43e16869-ad31-48e4-87ce-acf756709e18 |
+-------------------+--------------------------------------+

$ openstack subnet create \
  --network multisegment1 --network-segment segment1 \
  --ip-version 6 --subnet-range fd00:203:0:113::/64 \
  --ipv6-address-mode slaac multisegment1-segment1-v6
+-------------------+------------------------------------------------------+
| Field             | Value                                                |
+-------------------+------------------------------------------------------+
| allocation_pools  | fd00:203:0:113::2-fd00:203:0:113:ffff:ffff:ffff:ffff |
| cidr              | fd00:203:0:113::/64                                  |
| enable_dhcp       | True                                                 |
| gateway_ip        | fd00:203:0:113::1                                    |
| id                | e41cb069-9902-4c01-9e1c-268c8252256a                 |
| ip_version        | 6                                                    |
| ipv6_address_mode | slaac                                                |
| ipv6_ra_mode      | None                                                 |
| name              | multisegment1-segment1-v6                            |
| network_id        | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9                 |
| segment_id        | 43e16869-ad31-48e4-87ce-acf756709e18                 |
+-------------------+------------------------------------------------------+

Note

By default, IPv6 subnets on provider networks rely on physical network infrastructure for stateless address autoconfiguration (SLAAC) and router advertisement.

Create subnets on the segment2 segment. In this example, the IPv4 subnet uses 198.51.100.0/24 and the IPv6 subnet uses fd00:198:51:100::/64.

$ openstack subnet create \
  --network multisegment1 --network-segment segment2 \
  --ip-version 4 --subnet-range 198.51.100.0/24 \
  multisegment1-segment2-v4
+-------------------+--------------------------------------+
| Field             | Value                                |
+-------------------+--------------------------------------+
| allocation_pools  | 198.51.100.2-198.51.100.254          |
| cidr              | 198.51.100.0/24                      |
| enable_dhcp       | True                                 |
| gateway_ip        | 198.51.100.1                         |
| id                | 242755c2-f5fd-4e7d-bd7a-342ca95e50b2 |
| ip_version        | 4                                    |
| name              | multisegment1-segment2-v4            |
| network_id        | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 |
| segment_id        | 053b7925-9a89-4489-9992-e164c8cc8763 |
+-------------------+--------------------------------------+

$ openstack subnet create \
  --network multisegment1 --network-segment segment2 \
  --ip-version 6 --subnet-range fd00:198:51:100::/64 \
  --ipv6-address-mode slaac multisegment1-segment2-v6
+-------------------+--------------------------------------------------------+
| Field             | Value                                                  |
+-------------------+--------------------------------------------------------+
| allocation_pools  | fd00:198:51:100::2-fd00:198:51:100:ffff:ffff:ffff:ffff |
| cidr              | fd00:198:51:100::/64                                   |
| enable_dhcp       | True                                                   |
| gateway_ip        | fd00:198:51:100::1                                     |
| id                | b884c40e-9cfe-4d1b-a085-0a15488e9441                   |
| ip_version        | 6                                                      |
| ipv6_address_mode | slaac                                                  |
| ipv6_ra_mode      | None                                                   |
| name              | multisegment1-segment2-v6                              |
| network_id        | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9                   |
| segment_id        | 053b7925-9a89-4489-9992-e164c8cc8763                   |
+-------------------+--------------------------------------------------------+

Verify that each IPv4 subnet associates with at least one DHCP agent.

$ neutron dhcp-agent-list-hosting-net multisegment1
+--------------------------------------+-------------+----------------+-------+
| id                                   | host        | admin_state_up | alive |
+--------------------------------------+-------------+----------------+-------+
| c904ed10-922c-4c1a-84fd-d928abaf8f55 | compute0001 | True           | :-)   |
| e0b22cc0-d2a6-4f1c-b17c-27558e20b454 | compute0101 | True           | :-)   |
+--------------------------------------+-------------+----------------+-------+

Verify that inventories were created for each segment IPv4 subnet in the Compute service placement API (for the sake of brevity, only one of the segments is shown in this example).

$ SEGMENT_ID=053b7925-9a89-4489-9992-e164c8cc8763
$ curl -s -X GET \
  http://localhost/placement/resource_providers/$SEGMENT_ID/inventories \
  -H "Content-type: application/json" \
  -H "X-Auth-Token: $TOKEN" \
  -H "Openstack-Api-Version: placement 1.1"
{
    "resource_provider_generation": 1,
    "inventories": {
        "allocation_ratio": 1,
        "total": 254,
        "reserved": 2,
        "step_size": 1,
        "min_unit": 1,
        "max_unit": 1
    }
}

Note

As of the writing of this guide, there is not placement API CLI client, so the curl command is used for this example.

Verify that host aggregates were created for each segment in the Compute service (for the sake of brevity, only one of the segments is shown in this example).

$ nova aggregate-list
+----+---------------------------------------------------------+-------------------+
| Id | Name                                                    | Availability Zone |
+----+---------------------------------------------------------+-------------------+
| 10 | Neutron segment id 053b7925-9a89-4489-9992-e164c8cc8763 |                   |
+----+---------------------------------------------------------+-------------------+

Launch one or more instances. Each instance obtains IP addresses according to the segment it uses on the particular compute node.

Note

Creating a port and passing it to an instance yields a different behavior than conventional networks. The Networking service defers assignment of IP addresses to the port until the particular compute node becomes apparent. For example:

$ openstack port create --network multisegment1 port1
+-----------------------+--------------------------------------+
| Field                 | Value                                |
+-----------------------+--------------------------------------+
| admin_state_up        | UP                                   |
| binding_vnic_type     | normal                               |
| id                    | 6181fb47-7a74-4add-9b6b-f9837c1c90c4 |
| ip_allocation         | deferred                             |
| mac_address           | fa:16:3e:34:de:9b                    |
| name                  | port1                                |
| network_id            | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 |
| port_security_enabled | True                                 |
| security_groups       | e4fcef0d-e2c5-40c3-a385-9c33ac9289c5 |
| status                | DOWN                                 |
+-----------------------+--------------------------------------+