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openstack-manuals/doc/install-guide/source/neutron-initial-networks.rst

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Create initial networks

Before launching your first instance, you must create the necessary virtual network infrastructure to which the instances connect, including the external-network and tenant-network. After creating this infrastructure, we recommend that you verify-connectivity and resolve any issues before proceeding further. Initial networks <initialnetworks> provides a basic architectural overview of the components that Networking implements for the initial networks and shows how network traffic flows from the instance to the external network or Internet.

External network

The external network typically provides Internet access for your instances. By default, this network only allows Internet access from instances using Network Address Translation (NAT). You can enable Internet access to individual instances using a floating IP address and suitable security group rules. The admin tenant owns this network because it provides external network access for multiple tenants.

To create the external network

  1. On the controller node, source the admin credentials to gain access to admin-only CLI commands:

    $ source admin-openrc.sh

  2. Create the network:

    $ neutron net-create ext-net --router:external \
  --provider:physical_network external --provider:network_type flat
Created a new network:
+---------------------------+--------------------------------------+
| Field                     | Value                                |
+---------------------------+--------------------------------------+
| admin_state_up            | True                                 |
| id                        | 893aebb9-1c1e-48be-8908-6b947f3237b3 |
| name                      | ext-net                              |
| provider:network_type     | flat                                 |
| provider:physical_network | external                             |
| provider:segmentation_id  |                                      |
| router:external           | True                                 |
| shared                    | False                                |
| status                    | ACTIVE                               |
| subnets                   |                                      |
| tenant_id                 | 54cd044c64d5408b83f843d63624e0d8     |
+---------------------------+--------------------------------------+

Like a physical network, a virtual network requires a subnet assigned to it. The external network shares the same subnet and gateway associated with the physical network connected to the external interface on the network node. You should specify an exclusive slice of this subnet for router and floating IP addresses to prevent interference with other devices on the external network.

To create a subnet on the external network

Create the subnet:

$ neutron subnet-create ext-net EXTERNAL_NETWORK_CIDR --name ext-subnet \
  --allocation-pool start=FLOATING_IP_START,end=FLOATING_IP_END \
  --disable-dhcp --gateway EXTERNAL_NETWORK_GATEWAY
  • Replace FLOATING_IP_START and FLOATING_IP_END with the first and last IP addresses of the range that you want to allocate for floating IP addresses.
  • Replace EXTERNAL_NETWORK_CIDR with the subnet associated with the physical network.
  • Replace EXTERNAL_NETWORK_GATEWAY with the gateway associated with the physical network, typically the ".1" IP address.
  • You should disable DHCP on this subnet because instances do not connect directly to the external network and floating IP addresses require manual assignment.

For example, using 203.0.113.0/24 with floating IP address range 203.0.113.101 to 203.0.113.200:

$ neutron subnet-create ext-net 203.0.113.0/24 --name ext-subnet \
  --allocation-pool start=203.0.113.101,end=203.0.113.200 \
  --disable-dhcp --gateway 203.0.113.1
Created a new subnet:
+-------------------+------------------------------------------------------+
| Field             | Value                                                |
+-------------------+------------------------------------------------------+
| allocation_pools  | {"start": "203.0.113.101", "end": "203.0.113.200"}   |
| cidr              | 203.0.113.0/24                                       |
| dns_nameservers   |                                                      |
| enable_dhcp       | False                                                |
| gateway_ip        | 203.0.113.1                                          |
| host_routes       |                                                      |
| id                | 9159f0dc-2b63-41cf-bd7a-289309da1391                 |
| ip_version        | 4                                                    |
| ipv6_address_mode |                                                      |
| ipv6_ra_mode      |                                                      |
| name              | ext-subnet                                           |
| network_id        | 893aebb9-1c1e-48be-8908-6b947f3237b3                 |
| tenant_id         | 54cd044c64d5408b83f843d63624e0d8                     |
+-------------------+------------------------------------------------------+

Tenant network

The tenant network provides internal network access for instances. The architecture isolates this type of network from other tenants. The demo tenant owns this network because it only provides network access for instances within it.

To create the tenant network

  1. On the controller node, source the demo credentials to gain access to user-only CLI commands:

    $ source demo-openrc.sh

  2. Create the network:

    $ neutron net-create demo-net
Created a new network:
+-----------------+--------------------------------------+
| Field           | Value                                |
+-----------------+--------------------------------------+
| admin_state_up  | True                                 |
| id              | ac108952-6096-4243-adf4-bb6615b3de28 |
| name            | demo-net                             |
| router:external | False                                |
| shared          | False                                |
| status          | ACTIVE                               |
| subnets         |                                      |
| tenant_id       | cdef0071a0194d19ac6bb63802dc9bae     |
+-----------------+--------------------------------------+

Like the external network, your tenant network also requires a subnet attached to it. You can specify any valid subnet because the architecture isolates tenant networks. By default, this subnet uses DHCP so your instances can obtain IP addresses.

To create a subnet on the tenant network

Create the subnet:

$ neutron subnet-create demo-net TENANT_NETWORK_CIDR \
  --name demo-subnet --gateway TENANT_NETWORK_GATEWAY
  • Replace TENANT_NETWORK_CIDR with the subnet you want to associate with the tenant network.
  • Replace TENANT_NETWORK_GATEWAY with the gateway you want to associate with it, typically the ".1" IP address.

Example using 192.168.1.0/24:

$ neutron subnet-create demo-net 192.168.1.0/24 \
  --name demo-subnet --gateway 192.168.1.1
Created a new subnet:
+-------------------+------------------------------------------------------+
| Field             | Value                                                |
+-------------------+------------------------------------------------------+
| allocation_pools  | {"start": "192.168.1.2", "end": "192.168.1.254"}     |
| cidr              | 192.168.1.0/24                                       |
| dns_nameservers   |                                                      |
| enable_dhcp       | True                                                 |
| gateway_ip        | 192.168.1.1                                          |
| host_routes       |                                                      |
| id                | 69d38773-794a-4e49-b887-6de6734e792d                 |
| ip_version        | 4                                                    |
| ipv6_address_mode |                                                      |
| ipv6_ra_mode      |                                                      |
| name              | demo-subnet                                          |
| network_id        | ac108952-6096-4243-adf4-bb6615b3de28                 |
| tenant_id         | cdef0071a0194d19ac6bb63802dc9bae                     |
+-------------------+------------------------------------------------------+

A virtual router passes network traffic between two or more virtual networks. Each router requires one or more interfaces <interface> and/or gateways that provide access to specific networks. In this case, you create a router and attach your tenant and external networks to it.

To create a router on the tenant network and attach the external and tenant networks to it

  1. Create the router:

    $ neutron router-create demo-router
Created a new router:
+-----------------------+--------------------------------------+
| Field                 | Value                                |
+-----------------------+--------------------------------------+
| admin_state_up        | True                                 |
| external_gateway_info |                                      |
| id                    | 635660ae-a254-4feb-8993-295aa9ec6418 |
| name                  | demo-router                          |
| routes                |                                      |
| status                | ACTIVE                               |
| tenant_id             | cdef0071a0194d19ac6bb63802dc9bae     |
+-----------------------+--------------------------------------+

  2. Attach the router to the demo tenant subnet:

    $ neutron router-interface-add demo-router demo-subnet
Added interface b1a894fd-aee8-475c-9262-4342afdc1b58 to router demo-router.

  3. Attach the router to the external network by setting it as the gateway:

    $ neutron router-gateway-set demo-router ext-net
Set gateway for router demo-router

Verify connectivity

We recommend that you verify network connectivity and resolve any issues before proceeding further. Following the external network subnet example using 203.0.113.0/24, the tenant router gateway should occupy the lowest IP address in the floating IP address range, 203.0.113.101. If you configured your external physical network and virtual networks correctly, you should be able to ping this IP address from any host on your external physical network.

Note

If you are building your OpenStack nodes as virtual machines, you must configure the hypervisor to permit promiscuous mode on the external network.

To verify network connectivity

From a host on the external network, ping the tenant router gateway:

$ ping -c 4 203.0.113.101
PING 203.0.113.101 (203.0.113.101) 56(84) bytes of data.
64 bytes from 203.0.113.101: icmp_req=1 ttl=64 time=0.619 ms
64 bytes from 203.0.113.101: icmp_req=2 ttl=64 time=0.189 ms
64 bytes from 203.0.113.101: icmp_req=3 ttl=64 time=0.165 ms
64 bytes from 203.0.113.101: icmp_req=4 ttl=64 time=0.216 ms

--- 203.0.113.101 ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 2999ms
rtt min/avg/max/mdev = 0.165/0.297/0.619/0.187 ms