Deploying Dual-Stack IPv4 and IPv6 Networks

Doing an IPv6 implementation project does not involve tearing down an aging IPv4 network and replacing it with a new IPv6-enabled network. Instead, the IPv4 and IPv6 networks will run in parallel in what the industry calls a "dual-stack" network. But IPv4 and IPv6 are so significantly different in design that network management tools designed for an IPv4 network may not work the same in an IPv6 environment.

In this second installment of a three-part series on IPv6 implementation, Network Computing looks at the issues involved in deploying an IPv6 network alongside an IPv4 network.

The IPv6 protocol was established because the number of IPv4 addresses is quickly running out. The IPv6 protocol creates a 128-bit address, four times the size of the 32-bit IPv4 standard, so there will be infinitely more available IP addresses. This will accommodate all the smartphones, tablets and other computers on the network, but also the coming proliferation of Internet-connected devices including refrigerators, cars, and myriad sensors in homes, buildings and on IP networks.

With IPv6, a company may have exponentially more Internet addresses to use, but also more to manage, says Leslie Daigle, chief Internet technology officer for the Internet Society (ISOC), a global nonprofit organization that certifies technical standards for the Internet.

"The IPv6 address space is so large and your allocation is likely to be larger than you need it to be," she says. "On the flip side, that makes it a lot harder to probe your entire network because it is a much larger space."

The volume of available IP addresses adds to the network operator's workload because they have to probe the "dark spaces" within the network where there are no assigned IP addresses. "The managing and making sure that no one is squatting in your address space is considered to be a possible additional challenge," says Daigle.

The ISOC has created a Web portal, Deploy 360, to share information about how to deploy an IPv6-compliant network. On the site are a number of case studies on how IPv6 rollouts went, including one about the project at Oxford University in the United Kingdom. In an online report, Oxford's Guy Edwards detailed a five-step plan for deploying IPv6 alongside the existing IPv4 network.

First, Edwards advises, the organization should perform a network device audit, identifying all the routers, switches and firewalls on the network, as well as what specific versions of hardware and software are running. With the help of networking vendors, the next step is to determine which of the devices are already IPv6-compliant. He also advises that network administrators run a test on a particular IPv6 device to make sure that the software application to run on the network works.Second, Edwards says, perform an audit of services to run on the network, such as SMTP for e-mail and DNS for associating Internet domains and unique IP addresses. The audit should identify which of the network services may be IPv6-supported.

The next step is to build an IPv6-only test network and run the same services and applications that already run on the IPv4 network. In the test environment, document any differences in configuration syntax and behavior for setting up the service under IPv6.

The fourth step is to write a detailed IPv6 deployment plan that lays out in as much detail as possible how the rollout will occur. The plan should be shown to management for approval; it can also be peer-reviewed to make sure that nothing is overlooked.

Last, write a formal IP-addressing policy for going forward. This policy could also be peer-reviewed.

Some companies are going to discover that the network management tools designed to operate on an IPv4 network may not work the same way on an IPv6 network, says Jim Frey, managing research director at Enterprise Management Associates.

"There are still some challenges with how to manage these mixed environments. Underneath the covers there is actually, in many cases, a different set of data being drawn about the IPv6 traffic versus the IPv4 traffic."A network monitoring tool may reveal that maybe 5% or 10% of network traffic is IPv6 traffic, but it may not be able to identify which specific packets are IPv6, and some tools may not have been upgraded to support IPv6.

"It's still a work in progress to gain consistent visibility of mixed environments," says Frey.

Variables such as those described by Frey illustrate the need for a well-thought-out and well-executed rollout plan, says ISOC's Daigle.

"Any enterprise network operator knows that something done quickly is something done expensively," she says.

The third segment of this series--which first looked at how different networks have different IPv6 needs--will examine how to manage compliance and security in an IPv6 project.

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