SIDEBAR: 6 things to know about IPv6

What will World IPv6 Day prove?
Google, Facebook, Yahoo and 315 other companies, agencies and universities will provide Web content over both IPv6 and IPv4 for 24 hours. This will allow people who have IPv6 clients to use them to access many different sites. The idea is to expose any technical problems, such as misconfigurations in end-user equipment or software problems at carriers, that could keep users from getting on the Internet using the new protocol.
What would happen if I only had IPv6 and tried to go to an IPv4-only website?
In the worst case, you wouldn’t even get the familiar “server not found” message, according to Cricket Liu, vice president of architecture at Internet software vendor InfoBlox. This type of warning, also known as a “404” message, comes from the Web server of an existing domain that no longer hosts the page you’re looking for. Without a usable IP address, no Web server can be reached. “It would probably just give you some sort of a network error,” Liu said. Leo Vegoda, manager of number resources at the ICANN, said the message you receive will be up to your browser vendor.

So, would IPv6 cut me off from the Web?
In reality, you would probably get to see the website anyway, according to Liu. Service providers are evaluating a variety of tools for delivering IPv4-only content to IPv6-only clients. The most common one is a network address translation technique called NAT64, which can run on an appliance attached to a service provider’s network. When a name server can’t find an IPv6 address associated with the website that the user wants to visit, a NAT64 appliance can take the host’s IPv4 address and encapsulate it within an IPv6 address, creating something that the IPv6-only client can understand. Similarly, that appliance could allow users with different types of IP addresses to send e-mail to each other.

What if a site goes IPv6 and I’m still on IPv4?
That’s not likely to be a problem, at least in the next few years, because when companies adopt IPv6, most of them will use a “dual-stack” configuration, experts said. Dual network stacks contain all the software needed for communication with both IPv4 and IPv6 systems. When a client requests an IP address of either kind that’s associated with a given domain, they can get one. This is the system that’s really in place at most organizations that are using IPv6 today. “It’s not common to support v6, but if you do support v6, then it’s very common to run dual stack,” Liu said.

One ISP, Hurricane Electric, plans to offer NAT64 as a managed service, with the IPv6 address residing in its own data centers. Enterprises will be able to run their own servers on IPv4 and rely on Hurricane to link them to IPv6 users, according to Martin Levy, Hurricane’s director of IPv6 strategy. All the enterprises will need to do is add an entry to their DNS server, he said. Some Hurricane clients are already using the service in early release and will be using it on World IPv6 Day on Wednesday.

How long can I keep my company on IPv4?
As the supply of new, unique IPv4 addresses dwindles, some enterprises and service providers will use traditional NAT (network address translation) to conserve the addresses they already have. This technique, already used in everything from corporate LANs to home broadband routers, allows multiple clients on an internal network to share one or a few unique IPv4 addresses to talk to the Internet. Each shared IP address could keep as many as a few hundred systems chugging along without the need for new IPv4 or IPv6 addresses. In any case, IPv4 and IPv6 are expected to coexist on the Internet for many years to come.\

So why don’t we just use NAT instead of making people migrate?
NAT typically uses a stateful firewall, which has to maintain information about the ongoing Internet sessions that all the systems sharing an address are using, ICANN’s Vegoda said. The capacity of the appliance limits how many sessions it can keep track of, and if it reaches the limit, long-running sessions may be dropped. While this might not affect a five-minute YouTube video, it could cause problems for watching a full-length movie. In addition, some Internet applications use many sessions at once. For example, an online map may use a separate session for every tile of the map image, Vegoda said. If any of those sessions is broken, it could delay completing the map.

NAT64 doesn’t have to maintain state information. It is fundamentally different from traditional NAT and really shouldn’t even share its name, according to Hurricane Electric’s Levy. But even that technology can be a bottleneck. “If you put a box between source and destination of any variety that is interpreting the packets, you are going to affect the quality of the communication from one end to the other,” Levy said.

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