Chapter 3. Common administrative networking tasks

Create a network so that your instances can communicate with each other and receive IP addresses using DHCP. You can also integrate a network with external networks in your Red Hat OpenStack Platform deployment, or elsewhere, such as the physical network. This integration allows your instances to communicate with outside systems. For more information, see Bridge the physical network.

When creating networks, it is important to know that networks can host multiple subnets. This is useful if you intend to host distinctly different systems in the same network, and prefer a measure of isolation between them. For example, you can designate that only webserver traffic is present on one subnet, while database traffic traverses another. Subnets are isolated from each other, and any instance that wants to communicate with another subnet must have their traffic directed by a router. Consider placing systems that require a high volume of traffic amongst themselves in the same subnet, so that they do not require routing, and can avoid the subsequent latency and load.

Advanced network options are available for administrators, when creating a network from the Admin view. Use these options to specify projects and to define the network type that you want to use.

To create an advanced network, complete the following steps:

To allow traffic to be routed to and from your new network, you must add its subnet as an interface to an existing virtual router:

There are occasions where it becomes necessary to delete a network that was previously created, perhaps as housekeeping or as part of a decommissioning process. You must first remove or detach any interfaces where the network is still in use, before you can successfully delete a network.

To delete a network in your project, together with any dependent interfaces, complete the following steps:

Use the neutron purge command to delete all neutron resources that belong to a particular project.

For example, to purge the neutron resources of the test-project project prior to deletion, run the following commands:

# openstack project list
+----------------------------------+--------------+
| ID                               | Name         |
+----------------------------------+--------------+
| 02e501908c5b438dbc73536c10c9aac0 | test-project |
| 519e6344f82e4c079c8e2eabb690023b | services     |
| 80bf5732752a41128e612fe615c886c6 | demo         |
| 98a2f53c20ce4d50a40dac4a38016c69 | admin        |
+----------------------------------+--------------+

# neutron purge 02e501908c5b438dbc73536c10c9aac0
Purging resources: 100% complete.
Deleted 1 security_group, 1 router, 1 port, 1 network.

# openstack project delete 02e501908c5b438dbc73536c10c9aac0

Use subnets to grant network connectivity to instances. Each instance is assigned to a subnet as part of the instance creation process, therefore it’s important to consider proper placement of instances to best accommodate their connectivity requirements.

You can create subnets only in pre-existing networks. Remember that project networks in OpenStack Networking can host multiple subnets. This is useful if you intend to host distinctly different systems in the same network, and prefer a measure of isolation between them.

For example, you can designate that only webserver traffic is present on one subnet, while database traffic traverse another.

Subnets are isolated from each other, and any instance that wants to communicate with another subnet must have their traffic directed by a router. Therefore, you can lessen network latency and load by grouping systems in the same subnet that require a high volume of traffic between each other.

You can delete a subnet if it is no longer in use. However, if any instances are still configured to use the subnet, the deletion attempt fails and the dashboard displays an error message.

Complete the following steps to delete a specific subnet in a network:

OpenStack Networking provides routing services using an SDN-based virtual router. Routers are a requirement for your instances to communicate with external subnets, including those in the physical network. Routers and subnets connect using interfaces, with each subnet requiring its own interface to the router.

The default gateway of a router defines the next hop for any traffic received by the router. Its network is typically configured to route traffic to the external physical network using a virtual bridge.

To create a router, complete the following steps:

You can delete a router if it has no connected interfaces.

To remove its interfaces and delete a router, complete the following steps:

You can use interfaces to interconnect routers with subnets so that routers can direct any traffic that instances send to destinations outside of their intermediate subnet.

To add a router interface and connect the new interface to a subnet, complete these steps:

You can remove an interface to a subnet if you no longer require the router to direct traffic for the subnet.

To delete an interface, complete the following steps:

Follow the procedures in this section to manage your IP address allocation in OpenStack Networking.

# openstack subnet create --no-dhcp --allocation-pool start=IP_ADDRESS,end=IP_ADDRESS --gateway IP_ADDRESS --network SUBNET_RANGE NETWORK_NAME

# openstack subnet create --no-dhcp --allocation_pool start=192.168.100.20,end=192.168.100.100 --gateway 192.168.100.1 --network 192.168.100.0/24 public

# nova floating-ip-associate INSTANCE_NAME IP_ADDRESS

# nova floating-ip-associate corp-vm-01 192.168.100.20

OpenStack Networking supports one floating IP pool for each L3 agent. Therefore, you must scale your L3 agents to create additional floating IP pools.

Bridge your virtual network to the physical network to enable connectivity to and from virtual instances.

In this procedure, the example physical interface, eth0, is mapped to the bridge, br-ex; the virtual bridge acts as the intermediary between the physical network and any virtual networks.

As a result, all traffic traversing eth0 uses the configured Open vSwitch to reach instances.

For more information, see Chapter 11, Configuring bridge mappings.

To map a physical NIC to the virtual Open vSwitch bridge, complete the following steps: