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IPv6 transition: Observations from a name server perspective

By Dr. Burt Kaliski, Verisign chief technology officer, special to Network World
June 04, 2012 12:06 PM ET

Network World - As the operator of some of the core Internet name servers, including the DNS root, .com and .net, Verisign has a unique view into the challenges of transitioning to IPv6 and progress to date.

The purpose of a name server in the Domain Name System (DNS) is to translate the name of an Internet resource -- as examples, a website, a mail server or a mobile device -- to an Internet Protocol (IP) address. Domain names, such as, provide a textual, hierarchical identifier for an Internet resource in a higher-layer protocol such as HTTP. The corresponding IP address -- either the traditional 32-bit form in IP version 4 or the new 128-bit form in IP version 6 -- gives a routable, numeric identifier for the resource in lower-layer network communications.

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Thanks to the name-to-address translation provided by a DNS name server, when Verisign and other websites want to deliver content over IPv6, they don't need to use a different domain name (although they could do so). Rather, they can leave it to the Web browser, when running on an IPv6-enabled endpoint device, to look up an IPv6 address from the website's name server, and then to communicate with the website over IPv6. As a result, the grand upgrade currently underway from IPv4 to IPv6 largely impacts network communications, but not HTTP or other higher-layer protocols.

The simplicity of this higher-layer abstraction, of course, comes at a cost: The complexity of the implementations of services that translate between higher and lower layers of the stack.

DNS offers a good case study with its quadrupling of options due to IPv6. A name server hosts many "resource records," consisting of a domain name and associated information. Traditionally, requesters could only send DNS queries to look up resource records associated with a given domain name over the IPv4 protocol. Furthermore, if the associated information included an IP address, it could only be an IPv4 address (a so-called "A" record).

Now, if a name server is IPv6-enabled, requesters can send queries over either IPv4 or IPv6. In addition, the associated information can include either an IPv4 address or an IPv6 address (a so-called "AAAA" or "quad-A" record -- four times as many bits). The two choices are orthogonal, so overall there are four times as many options as before. This initial complexity is just the starting point, however, because of the recursive nature of DNS, which may result in transactions with additional name servers, some of which may be IPv6-enabled, and some not, in the search for an ultimate IPv4 or IPv6 address.

Operators of the authoritative name servers for large top-level domains (TLDs) have a privileged "observation point" for the transition from IPv4 to IPv6, relative to the "zone" or set of domain names for which the name server is authoritative. Verisign has been studying trends in the zones it operates name servers for -- including the DNS root, .com and .net, such as:

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