Routed provider networks

Note

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. Neutron port could be associated with only one network segment, but there is an exception for OVN distributed services like OVN Metadata.

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.

Prerequisites

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

  1. 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.

  2. 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

  3. 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

    …

    …

    …

  4. 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

    …

    …

    …

  5. 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

  1. 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

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

    [placement]
www_authenticate_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

  3. Restart the neutron-server service.

  4. (Optional) Configure the Nova scheduler to filter based upon routed network host aggregates. Without this option set, once ports are attached to instances and have IP addresses assigned, Nova may schedule instances to hosts which do not have access to the required segment. See the Nova configuration reference for more information.

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.

  1. Source the administrative project credentials.

  2. 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                                 |
| revision_number           | 1                                    |
| router:external           | Internal                             |
| shared                    | True                                 |
| status                    | ACTIVE                               |
| subnets                   |                                      |
| tags                      | []                                   |
+---------------------------+--------------------------------------+

  3. 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.

  4. Create a second segment on the provider network. In this example, the segment uses the provider2 physical network with VLAN ID 2017.

    $ openstack network segment create --physical-network provider2 \
  --network-type vlan --segment 2017 --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                            |
| revision_number  | 1                                    |
| segmentation_id  | 2017                                 |
| tags             | []                                   |
+------------------+--------------------------------------+

  5. 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         |    2017 |
| 43e16869-ad31-48e4-87ce-acf756709e18 | segment1 | 6ab19caa-dda9-4b3d-abc4-5b8f435b98d9 | vlan         |    2016 |
+--------------------------------------+----------+--------------------------------------+--------------+---------+

  6. 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 |
| revision_number   | 1                                    |
| segment_id        | 43e16869-ad31-48e4-87ce-acf756709e18 |
| tags              | []                                   |
+-------------------+--------------------------------------+

$ 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                 |
| revision_number   | 1                                    |
| segment_id        | 43e16869-ad31-48e4-87ce-acf756709e18                 |
| tags              | []                                                   |
+-------------------+------------------------------------------------------+

    Note

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

  7. 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 |
| revision_number   | 1                                    |
| segment_id        | 053b7925-9a89-4489-9992-e164c8cc8763 |
| tags              | []                                   |
+-------------------+--------------------------------------+

$ 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                   |
| revision_number   | 1                                                      |
| segment_id        | 053b7925-9a89-4489-9992-e164c8cc8763                   |
| tags              | []                                                     |
+-------------------+--------------------------------------------------------+

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

    $ openstack network agent list --agent-type dhcp --network multisegment1
+--------------------------------------+------------+-------------+-------------------+-------+-------+--------------------+
| ID                                   | Agent Type | Host        | Availability Zone | Alive | State | Binary             |
+--------------------------------------+------------+-------------+-------------------+-------+-------+--------------------+
| c904ed10-922c-4c1a-84fd-d928abaf8f55 | DHCP agent | compute0001 | nova              | :-)   | UP    | neutron-dhcp-agent |
| e0b22cc0-d2a6-4f1c-b17c-27558e20b454 | DHCP agent | compute0101 | nova              | :-)   | UP    | neutron-dhcp-agent |
+--------------------------------------+------------+-------------+-------------------+-------+-------+--------------------+

  9. 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
$ openstack resource provider inventory list $SEGMENT_ID
+----------------+------------------+----------+----------+-----------+----------+-------+
| resource_class | allocation_ratio | max_unit | reserved | step_size | min_unit | total |
+----------------+------------------+----------+----------+-----------+----------+-------+
| IPV4_ADDRESS   |              1.0 |        1 |        2 |         1 |        1 |    30 |
+----------------+------------------+----------+----------+-----------+----------+-------+

  10. 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).

    $ openstack aggregate list
+----+---------------------------------------------------------+-------------------+
| Id | Name                                                    | Availability Zone |
+----+---------------------------------------------------------+-------------------+
| 10 | Neutron segment id 053b7925-9a89-4489-9992-e164c8cc8763 | None              |
+----+---------------------------------------------------------+-------------------+

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

    Note

    If a fixed IP is specified by the user in the port create request, that particular IP is allocated immediately to the port. However, creating a port and passing it to an instance yields a different behavior than conventional networks. If the fixed IP is not specified on the port create request, 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                                 |
| revision_number       | 1                                    |
| security_groups       | e4fcef0d-e2c5-40c3-a385-9c33ac9289c5 |
| status                | DOWN                                 |
| tags                  | []                                   |
+-----------------------+--------------------------------------+

Migrating non-routed networks to routed

Migration of existing non-routed networks is only possible if there is only one segment and one subnet on the network. To migrate a candidate network, update the subnet and set id of the existing network segment as segment_id.

Note

In the case where there are multiple subnets or segments it is not possible to safely migrate. The reason for this is that in non-routed networks addresses from the subnet’s allocation pools are assigned to ports without considering to which network segment the port is bound.

Example

The following steps migrate an existing non-routed network with one subnet and one segment to a routed one.

  1. Source the administrative project credentials.

  2. Get the id of the current network segment on the network that is being migrated.

    $ openstack network segment list --network my_network
+--------------------------------------+------+--------------------------------------+--------------+---------+
| ID                                   | Name | Network                              | Network Type | Segment |
+--------------------------------------+------+--------------------------------------+--------------+---------+
| 81e5453d-4c9f-43a5-8ddf-feaf3937e8c7 | None | 45e84575-2918-471c-95c0-018b961a2984 | flat         | None    |
+--------------------------------------+------+--------------------------------------+--------------+---------+

  3. Get the id or name of the current subnet on the network.

    $ openstack subnet list --network my_network
+--------------------------------------+-----------+--------------------------------------+---------------+
| ID                                   | Name      | Network                              | Subnet        |
+--------------------------------------+-----------+--------------------------------------+---------------+
| 71d931d2-0328-46ae-93bc-126caf794307 | my_subnet | 45e84575-2918-471c-95c0-018b961a2984 | 172.24.4.0/24 |
+--------------------------------------+-----------+--------------------------------------+---------------+

  4. Verify the current segment_id of the subnet is None.

    $ openstack subnet show my_subnet --c segment_id
+------------+-------+
| Field      | Value |
+------------+-------+
| segment_id | None  |
+------------+-------+

  5. Update the segment_id of the subnet.

    $ openstack subnet set --network-segment 81e5453d-4c9f-43a5-8ddf-feaf3937e8c7 my_subnet

  6. Verify that the subnet is now associated with the desired network segment.

    $ openstack subnet show my_subnet --c segment_id
+------------+--------------------------------------+
| Field      | Value                                |
+------------+--------------------------------------+
| segment_id | 81e5453d-4c9f-43a5-8ddf-feaf3937e8c7 |
+------------+--------------------------------------+

Routed provider networks as external networks for tenant routed networks

Note

This section applies only to legacy routers, not DVR nor HA routers. A legacy router has a single instance that is hosted in one single host.

One of the consequences of this feature is the externalization of any routing operation. The communication (routing) between segments is done using the underlying network infrastructure, not managed by Neutron.

Could be the case that the user needs to split the communication between several hosts. It is possible to create tenant networks and connect them using a router. To access to the routed provider network, it should be connected as router gateway.

Tenant net1  ┌─────────────────────┐
─────────────┤                     │
             │                     │ Routed provided network
             │             GW port ├────────────────────────
Tenant net2  │                     │
─────────────┤                     │
             └─────────────────────┘

The routed provider network, acting as router gateway, contains all subnets associated to the segments. In a deployment without routed provided networks, the gateway port has L2 connectivity to all subnet CIDRs. In this case, the gateway port has only connectivity to the attached segment subnets and its L2 broadcast domains.

The L3 agent will create, inside the router namespace, a default route in the gateway port fixed IP CIDR. For each other subnet not belonging to the port’s fixed IP address, an onlink route is created. These routes use the gateway port as routing device and allow to route any packet with destination on these CIDRs through this port.

The problem in the case of connecting the gatewat port to a routed provider network is that it will have broadcast connectivity only to those subnets that belong to the host segment:

  • One of those subnets will provide the port IP address. The gateway IP address of this subnet will be the default route, through the gateway port.

  • Any other subnet belonging to this segment will create a onlink route, using the gateway port as route device.

For example, let’s consider the following configuration:

  • Two tenant networks with CIDRs 10.1.0.0/24 and 10.2.0.0/24.

  • A RPN with two segments; each segment with two subnets: segment 1 with 10.51.0.0/24 and 10.52.0.0/24, segment 2 with 10.53.0.0/24 and 10.54.0.0/24.

  • The router is connected to the first segment and the gateway port has an IP address in the range of 10.51.0.0/24. This is why the default route uses an IP address in this range.

Without considering that the gateway network is a router provided network, this is the routing table set in the router namespace:

$ ip netns exec $r ip r
default via 10.51.0.1 dev qg-gwport proto static
10.1.0.0/24 dev qr-tenant1 proto kernel scope link src 10.1.0.1
10.2.0.0/24 dev qr-tenant2 proto kernel scope link src 10.2.0.1
10.51.0.0/24 dev qg-gwport proto kernel scope link src 10.100.0.15
10.52.0.0/24 dev qg-gwport proto static scope link
10.53.0.0/24 dev qg-gwport proto static scope link  <-- should be removed, belongs to segment 2
10.54.0.0/24 dev qg-gwport proto static scope link  <-- should be removed, belongs to segment 2

Those packets sent to 10.53.0.0/24 and 10.54.0.0/24 (the second RPN subnet CIDRs), don’t have L2 connectivity and the ARP packets won’t be replied. In the case of having a RPN as gateway network, all packets exiting the router through the gateway, must be sent to the gateway IP address, in this case 10.51.0.1. This is why the L3 plugin does not send the information of other segments subnets L3 agent when:

  • The network is the router gateway.

  • The “segments” plugin is enabled; this plugin is needed for routed provided networks.

  • The network is connected to a segment.