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Extending virtual networks over WANs: What a WAN manager needs to know

Kumar Reddy, author of “Network Virtualization,” discusses extending virtual networks over the WAN, providing necessary knowledge to a WAN manager. spoke with Kumar Reddy, one of the authors of Network Virtualization, about extending virtual...

networks over the WAN. We asked Reddy questions including: What are the challenges of extending virtual networks over the WAN? What preparations should a WAN manager make? Get the answers to these and other questions in this Q&A.

What does it mean to “extend a virtual network over a WAN?”

Kumar Reddy: Let’s first define what a virtual network is. A virtual network is a multiple, logical network that runs over a shared physical infrastructure. A virtual network will connect devices, users and lots of different sites [together]. To connect the sites together, you have to expand the virtual network that you’ve hooked up with these different sites across a WAN. So when you’re talking about extending the virtual network over a WAN, you extend all your virtualized networks across usually someone else’s network.

How does that compare to the definition of a “virtual wide area network”?

Reddy: A virtual wide area network  is something that probably involves using a single network just by itself. Virtualization gives you the ability to leverage a single virtual network connect by creating it once and [allowing you to] reuse it many times. That's the secret of virtualization: Being able to reuse … an old part of the network so you don’t have to create these things a zillion times.

Why might an enterprise need to extend the virtualized network over the WAN?

Reddy: There are two parts to the answer. One is, just like physical networks, virtual networks need to connect multiple sites and people to be useful. By necessity, this requires virtualizing the campus, data center and WAN to allow for end-to-end reachability. The second part is [understanding] why virtualization is important in the first place for networking. You’re basically trying to create separate groups of users because you may have contacts to keep apart; you may have different user populations that need [secure, remote] access … you may have compliance requirements; you may have moved in an acquisition. Those are some of the business drivers behind the technology.

What is the most challenging aspect of extending virtual networks over the WAN for enterprises?

Reddy: There are multiple technology options that exist today with varying degrees of flexibility and complexity. You can go very high-end [to get] lots of flexibility and scale. Or you can get relatively simple [devices] … but in each case, it’s a change from a physical world to a virtualized world that involves a change of thinking, and it involves a change of procedure and operations. People have lived through this in the server space which is virtualized today, and the same [will happen] in the networking space.

What preparations do enterprises need to make for maintaining virtual networks over the WAN? What is the process like?

Reddy: The first part of the process is to deal with the training, tutoring, operations and the management of the infrastructure you're going to virtualize. The second part is to do a bit of planning and not go overboard. Some good questions to ask are how many virtual networks do I need, and do I have enough capacity to get to where I think I need to go in a reasonable amount of time?  Also [ask yourself,] ‘What sort of virtual connectivity do I want?’ because when you virtualize, the network comes in all sizes. In a virtual network you can have a subset of sites that are connected. So what is the virtual topology going to be and what will it become?

What do you recommend to a WAN manager who has little experience in maintaining virtual networks?

Reddy: Start with what you know and avoid disruptions to your network. It’s possible today to take an existing enterprise campus-wide design and virtualize it with essentially the same architecture. Once you can do the design, you can run it many times and that will have certain scaling properties. As your needs grow and the team becomes more familiar with the virtualization technology,  there’s an opportunity to change the architecture to get something more scalable and more flexible.

Why would enterprises not deploy virtual networks over the WAN? What might prevent enterprises from doing so?

Reddy: Probably the process more than anything else [would keep enterprises from deploying virtual networks]. I think on the technology side, there’s always a way. Technology is always serving some higher business need, so you have to ask, ‘Do you have the right operation in place? Do you have the right tutoring and training in place?’ Virtualizing the WAN is something that’s done with great regularity … with companies big and small.

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