Network virtualization technology FAQ

Network virtualization lets you break one physical network into many virtual networks or combine physical networks into one virtual network.

It’s no secret that server virtualization affects the network. So for some organizations, virtualizing the network itself makes a lot of sense.

Network virtualization technology allows administrators to consolidate multiple networks, divide a single network into many or create software-only networks between virtual machines (VMs). The goal of network virtualization is to improve speed, automation and network management. Network virtualization technology also binds separate physical network switches into one virtual switch, which saves space and reduces power and cabling costs.

Virtualizing a network begins with combining network resources and dividing available bandwidth into independent channels. You can assign these channels to particular servers or devices in real time. Using virtual network software, you can emulate network connectivity among VMs on a physical host. Or, with external network virtualization, combine several physical networks into one or more virtual networks.

With all these benefits, network virtualization technology is becoming more popular. Throughout 2011, organizations will start focusing even more on network virtualization security and management tools. The answers to these questions reveal the pros and cons of virtual networks as well as everything you need to know about virtual switches, network consolidation and virtual network management.

What does virtual network software do?

Depending on the size and type of your virtualization platform, you can place virtual network software inside or outside a virtual server. External software uses switches, adapters, network storage devices and Ethernet or Fibre Channel to aggregate physical LANs into a single logical LAN, or to break a physical LAN into multiple virtual LANs (VLANs). Internal software allows VMs to exchange data on a host without an external network, which boosts VM performance and security.

Different hypervisors support different network virtualization methods, but whichever type of software you choose, be aware that managing a virtual network is tricky. You need comprehensive documentation and virtual network management tools to keep track of multiple abstracted networks running on a physical LAN.

What are the benefits of virtual networks?

Many people still see network virtualization technology as new, but it should really be considered a next step for server virtualization admins. Network virtualization comes with plenty of benefits to help convince customers: cost savings, rapid provisioning and scalability. Some administrators might even use network virtualization services without even knowing it. Products such as VMware vShield, vSphere vNetwork switches and Cisco Systems’ Nexus 1000V all help to create virtual networks. But it takes research, planning and cooperation between network and server virtualization teams to begin the process.

How does a virtual switch affect the network?

When you virtualize an infrastructure, a virtual switch connects hosts so that IP traffic can move across the network. But doing so can introduce complexity, because you often need to manually configure a virtual switch on each server. To solve that problem, VMware developed a distributed virtual switch (vSwitch), which spans ports and management across all servers in a cluster. It can also be difficult to manage larger virtual networks that span data centers or disaster recovery sites, so it’s important to consider the number of Ethernet connections your servers require.

What are some common problems with virtual network management?

Organizational politics and virtual network switch challenges often complicate virtual network management. Virtualization administrators usually manage the virtual switch, which can create friction with network admins, because they no longer control part of the network (the part inside the hosts). Plus, much of the traffic between VMs on the same host never leaves the host, so it doesn’t go over the physical network, making it difficult to monitor traffic with traditional devices.

Overall, network virtualization can weaken security and manageability. But Cisco Systems’ Nexus 1000V distributed virtual switch shifts virtual network management inside a host back to network admins and increases network security. Other products such as Reflex Systems’ Virtual Management Center, Altor Networks’ Virtual Firewall and Catbird’s vSecurity can also improve virtual network management.

When should I use a virtual network appliance?

Like network virtualization, virtual network appliances aren’t necessarily useful in all infrastructures. The main benefit of virtual appliances is that you can deploy them on demand. But when you repackage a networking appliance into VM format, it can’t rely on dedicated hardware, and its resource consumption sometimes hurts performance. If you’re using CPU-intensive network appliances, though, those may be good virtualization candidates.

Virtual network appliances are also useful for virtual network management in multi-tenant clouds. And if firewall and routing functions are implemented as part of the virtual switch, rather than relying on the VMs, virtualizing network appliances could help improve traffic flow.

Can I apply network virtualization to wide area networks?

Yes, network virtualization technology can greatly benefit wide area networks (WANs). It can help allocate WAN bandwidth, improve network speed and simplify WAN management. For one, managing virtualized WANs is easier, because you can cluster network devices and make them appear as a single device. Plus, the network appears as dedicated contiguous channels, allowing admins to trace a VLAN from server to LAN to WAN to end user for troubleshooting and capacity planning.

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