RHEV 3 networking basics: Setting up a logical network

Networking is an important part of any virtual data center. Red Hat Enterprise Virtualization sets up a management network automatically, but one network may not be enough. It's also important to add at least one logical network in a RHEV 3 environment.

Logical networking

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is used to connect virtual machines (VMs) to external users or storage. To maintain flexibility and avoid overtaxing network hardware, it is a good idea to set up at least one additional logical network to separate management traffic from other network traffic.

Often, data centers have separate logical networks for guest data, storage access, management and, in some cases, the display network. The management network carries traffic between different hosts, and an administrator uses the display network to access VM consoles.

Make sure the physical network to which the logical network is assigned has been completely configured before you begin. Before setting up a logical network, it's also a good idea to put all hosts that will access the network in maintenance mode. Changing network settings on running hosts may make the host unreachable. Making network changes is not something to take lightly, and administrators should carefully plan a maintenance window in which an unavailable host won't disrupt users.

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Step-by-step process for adding virtual hosts in RHEV-M

There are just a few parameters to set when creating a logical network in Red Hat Enterprise Virtualization (RHEV), including if you want to use spanning tree protocol (STP) and virtual LAN (VLAN) tagging. STP allows logical switches in the network to connect nodes and communicate their status with external networks. In general, it's best not to use STP in virtualized network environments, because if incorrectly configured, a switching loop can bring down network traffic on the entire switching infrastructure. 

VLAN tagging is a useful option that allows you to assign a logical network to a specific VLAN. Because most physical networks make use of VLAN technology, VLAN tagging makes sense.

After creating a logical network, you need to assign the hosts that are going to use it. Make sure the logical network is associated to a physical network interface card in each host in the cluster, or else you won't be able to activate the host.

Configuring the network interface is not difficult. First, set up the physical network infrastructure. Every logical network needs a dedicated physical network interface; it is not possible to share an interface between several networks. If you want to use network bonding, be sure it's configured on all hosts before proceeding.

Once all physical networking is configured, select the host and the network interface to which you want to assign to the network.. This gives access to an interface where you can specify the IP address and whether RHEV should check connectivity on this interface.

If you opt to allow RHEV to check connectivity, the network will automatically shut down if a cable is temporarily unplugged. Once you've configured all settings you want to use, check the"Save network configuration" box in the bottom part of the Edit Network window and click "OK" to save the configuration.

Once the network has been configured, you can edit current settings or temporarily detach the network from the management interface. Doing this allows you to perform maintenance on a specific interface, which means you won't have to bring down the entire network to apply changes to just one network interface.

This was first published in November 2012

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