Create a Network


This guide explains networking in OpenStack including how to create a private network, a router, and allocate and assign floating IPs.

You will learn how to create a private network on which instances will be deployed. The network created in this guide will be used later when creating an instance.

Neutron is the service that manages networking in OpenStack and allows for networks, routers, floating IPs, and security groups to be created. It provides “network connectivity as a service” between interfaces and uses the OpenStack Networking API.

Create a Network and Router

This section demonstrates creating a private network and router. The router is important as it will allow you to create a route between networks, such as from the private network to the Internet.

This section explains how to make a network and router using the command line with OpenStackClient.

Create a network

Listed are the steps needed to create a private network. Variables are presented in all capital and should be replaced accordingly. Note the output of most of the commands has been truncated.

Note! — Private networks should be used where possible. Only expose the portions of your cloud to a public network when needed.

Step 1 — Create private network

Use this command to create a network, replacing NETWORK_NAME with the name of the network:

$ openstack network create NETWORK_NAME

Create a network called network-1:

$ openstack network create network-1
| Field                     | Value                                |
| admin_state_up            | UP                                   |
| availability_zone_hints   |                                      |
| availability_zones        |                                      |
| created_at                | 2021-05-19T20:13:29Z                 |
| description               |                                      |
| dns_domain                | None                                 |
| id                        | 0a193fa1-2019-4fbc-a862-6f6ced157c1e |

Step 2 — Create subnet

Next, a subnet will need to be created.

Use this command to create a subnet, replacing NETWORK_NAME and SUBNET_NAME with the respective names of the network and subnet and replace SUBNET_RANGE with the subnet to use. An example subnet range could be

$ openstack subnet create --subnet-range SUBNET_RANGE --network NETWORK_NAME 

Create a subnet called subnet-1 with subnet range of

$ openstack subnet create --subnet-range --network network-1 subnet-1
| Field                | Value                                |
| allocation_pools     |                  |
| cidr                 |                          |
| created_at           | 2021-05-19T20:22:03Z                 |
| description          |                                      |
| dns_nameservers      |                                      |
| dns_publish_fixed_ip | None                                 |
| enable_dhcp          | True                                 |
| gateway_ip           |                             |

Step 3 — Show network details

You can list the network and subnet and show more information about each.

List networks using:

$ openstack network list
| ID                                   | Name      | Subnets                              |
| 0a193fa1-2019-4fbc-a862-6f6ced157c1e | network-1 | df4d6183-9c3b-4bb9-a686-cf1fc7d60f7f |
| 5cc755c9-41fc-44c2-87e7-642dfdfb0208 | External  | a52754dd-13d9-4a36-bab6-10058f4887f5 |

List subnets using:

$ openstack subnet list
| ID                                   | Name     | Network                              | Subnet            |
| a52754dd-13d9-4a36-bab6-10058f4887f5 | Internet | 5cc755c9-41fc-44c2-87e7-642dfdfb0208 | |
| df4d6183-9c3b-4bb9-a686-cf1fc7d60f7f | subnet-1 | 0a193fa1-2019-4fbc-a862-6f6ced157c1e |       |

To get more information about each, use the show subcommand and specify the UUID for the network and subnet:

$ openstack network show 0a193fa1-2019-4fbc-a862-6f6ced157c1e
$ openstack subnet show df4d6183-9c3b-4bb9-a686-cf1fc7d60f7f

Create a Router

With a network created, the next step is to create a router which will bridge the connection from the External or provider network to the private network.

Step 1 — Create router

To make a router, use this base command, replacing ROUTER_NAME with the name of the router:

$ openstack router create ROUTER_NAME

Create a router called router-1:

$ openstack router create router-1
| Field                   | Value                                |
| admin_state_up          | UP                                   |
| availability_zone_hints |                                      |
| availability_zones      |                                      |
| created_at              | 2021-05-19T20:35:14Z                 |

Step 2 — Attach interfaces

With the router created, the External and subnet-1 interfaces need to be attached to it.

To add a subnet, use this command, replacing ROUTER_NAME and SUBNET_NAME with the names of the respective router and subnet:

$ openstack router add subnet ROUTER_NAME SUBNET_NAME

Attach subnet:

Add subnet subnet-1 to the router called router-1:

$ openstack router add subnet router-1 subnet-1

The command to add the subnet to the router returns no output if successful.

Attach External network:

To finish setting up the router, attach the External network to it.

Use this command to add the external network, replacing EXTERNAL_NETWORK_UUID with the UUID of the network:

$ openstack router set --external-gateway EXTERNAL_NETWORK_UUID 

Obtain the UUID of the External network by running openstack network list. The UUID will be listed in the first column.

Add the external network to the router called router-1:

$ openstack router set --external-gateway 
5cc755c9-41fc-44c2-87e7-642dfdfb0208 router-1

Step 4 — Confirm router details

With these steps completed, you have a router that connects the external network to the private network.

You can see the details of the router by running the following, replacing ROUTER_NAME with the name of the router:

$ openstack router show ROUTER_NAME

Show the details for the router called router-1, including the interfaces that were previously attached:

$ openstack router show router-1 --fit-width
| Field                   | Value                                                                                               |
| admin_state_up          | UP                                                                                                  |
| availability_zone_hints |                                                                                                     |
| availability_zones      | nova                                                                                                |
| created_at              | 2021-05-19T20:35:14Z                                                                                |
| description             |                                                                                                     |
| external_gateway_info   | {"network_id": "5cc755c9-41fc-44c2-87e7-642dfdfb0208", "external_fixed_ips": [{"subnet_id":         |
|                         | "a52754dd-13d9-4a36-bab6-10058f4887f5", "ip_address": ""}], "enable_snat": true}      |
| flavor_id               | None                                                                                                |
| id                      | d5b0eb30-8b2a-4f2e-a9df-4ad7ee792cec                                                                |
| interfaces_info         | [{"port_id": "fa1f794f-5101-4df4-b83a-3c260d0a65fa", "ip_address": "", "subnet_id":         |
|                         | "df4d6183-9c3b-4bb9-a686-cf1fc7d60f7f"}]                                                            |
| name                    | router-1                                                                                            |

Floating IPs

Floating IPs in OpenStack are publicly routable IP addresses that can be attached and detached to instances. For example if there’s an instance associated with a private network but needs to be accessed from the Internet, a floating IP can be associated with the instance, allowing communication from the Internet.

Allocate and Assign Floating IPs

To use Floating IPs they will first need to be allocated from the provider network’s pool of IPs. The following is a list of commands used to manage floating IPs.

Step 1 — Allocate floating IP

Allocate additional floating IPs where NETWORK is the UUID of the network to allocate IPs from:

$ openstack floating ip create NETWORK

You will need to first obtain the External network’s UUID using openstack network list.

Allocate a floating IP from the External network:

$ openstack floating ip create 5cc755c9-41fc-44c2-87e7-642dfdfb0208
| Field               | Value                                |
| created_at          | 2021-05-19T20:54:19Z                 |
| description         |                                      |
| dns_domain          | None                                 |
| dns_name            | None                                 |
| fixed_ip_address    | None                                 |
| floating_ip_address |                       |

Step 2 — List floating IPs

Make use of openstack floating ip list to view floating IPs. You will see the IP allocated from the previous section.

List floating IPs:

$ openstack floating ip list
| ID                                   | Floating IP Address | Fixed IP Address | Port | Floating Network                     | Project                          |
| 99d58cc0-1b27-4171-aa44-6c15d15718fa |      | None             | None | 5cc755c9-41fc-44c2-87e7-642dfdfb0208 | fece7ddb8663497bb99ee0988719143c |

This floating IP will be used later to access an instance over SSH.

Next Steps

The next guide is Manage OpenStack Images and explains how to work with images.

Nick West Systems Engineer

Nick is an avid aggressive inline skater, nature enthusiast, and loves working with open source software in a Linux environment.

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