Networking in OpenStack

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.

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

Neutron is the name of the service that manages networking in OpenStack.
It provides “network connectivity as a service” between interfaces and uses
the OpenStack Networking API.

Neutron allows networks, routers, floating IPs, and security groups to be

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.

Create a network

Step 1 — Getting started

In Horizon, notice the sections on the left called Project and
Identity. Components of an OpenStack cloud, like a private network, are
created through the Project tab.
um project identity



To create a network, under Project on the left, find Network, then
navigate to Networks. Finally, locate the Create Network button near
the top right.
um network networks



Step 2 — Create network
um create a network form

  • Network Name — This is the name of the network. In this example, the
    network is called network-1.
  • Enable Admin State — This enables the network and should remain
  • Create Subnet — Leave checked to create a subnet.
  • Availability Zone Hints — This option’s default is sufficient for this

Fill out any other needed details and navigate to the Subnet tab.


Step 3 — Create subnet
um create a subnet form

  • Subnet Name — Specify a name for the subnet, this example is called
  • Network Address — Choose a network in CIDR notation. This example uses
  • Gateway IP — Optionally choose the gateway IP for this network. If the
    gateway IP is not filled out, one will be chosen by the neutron service.
    The final tab is called Subnet Details. This tab does not need to be
    filled out to create the network and subnet. This example will stop here,
    however on this page you can enable or disable DHCP, specify specific IPs to
    be allocated, set DNS name servers, and set Host Routes.


Step 4 — Confirm network creation

With the previous steps done, the network has been created. Loading the
Network -> Networks tab will display the new network:
um network listing


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

Step 1 — Getting started


To make a router in Horizon, under Project, find the Network section,
then Routers under that. This page will list current routers and allows
you to create a router.

To create a new router, click the Create Router button near the top
um router main page

Step 2 — Create a router
um create router

  • Router Name — Choose a name for the router. This example router will
    be called router-1.
  • Enable Admin State — Leave checked to enable the router.
  • External Network — The External network will be used
  • Availability Zone Hints — This option’s default is sufficient for this

The router will need to be connected to an external network, which will be
the provider network. The network called External will be used.



Step 3 — Confirm the router has been created

Once created it will show in the list of routers, under Network -> Routers.
um router list

Step 4 — Connect router to private network

To allow the router to communicate with the External and the network-1
network, the network-1 network will need to be attached. Connecting the
router to a network is called attaching an interface.

First, pull up the newly created router from the Network -> Routers
section of Horizon.

Next, to add an interface to this router, click the router’s name in the listing of routers, then click the Add Interface button near the top right.
um add interface router

In the following choose the subnet-1 subnet to connect the router to and
optionally choose an IP address for the interface. If you don’t choose an IP,
the gateway IP of the subnet will be used.
um router add interface

Step 5 — Confirm the networks are connected

With the interface added to the router, the External and network-1
networks are now connected. This can visually be seen by navigating to the
Network tab on the left, then the Network Topology tab under that.
um network topology


Floating IPs

Floating IPs in OpenStack are publicy 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.

Allocate floating IP


To allocate floating IPs in Horizon, navigate to the Network tab on the
left, and find Floating IPs.
um floating ips
Click Allocate IP To Project to allocate a new IP.


Next, fill out needed details in the IP allocation form.
um allocate floating ip
The IP will be obtained from the External provider network. This is the
only network floating IPs can be assigned from.

Once the IP is added, it will appear in the floating IP list.
um floating ip listing

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


Next Steps

The next guide goes over images in OpenStack, which are bootable operating systems.

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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