IPv6 transition: Observations from a name server perspective
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 www.VerisignInc.com, 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:
• The percentage of domain names in a given zone that are served by an IPv6-enabled name server (vs. IPv4-only).
• The percentage of DNS queries received via the IPv6 protocol (vs. IPv4).
• The percentage of DNS queries that request a quad-A record (vs. an A record).
Already, there has been a steady increase in the percentage of DNS queries over the IPv6 protocol at the two root name servers that Verisign operates. Labeled "A root" and "J root," these are two of the 13 name servers that requesters can contact to get the IP addresses of name servers for top-level domains. From May 2011 to May 2012, the percentage of queries to the A and J root name servers received over IPv6 has tripled, from just over 1% to between 3% and 4%. (This current rate is consistent with what we're aware of for other root name servers.) The percentage of queries over IPv6 to the name servers for .com and .net is still steady at just under 1%. Occasional fluctuations can be due to trial deployments of IPv6 at various parts of the Internet, or other variations in the mix of IPv4 vs. IPv6 traffic.
The steady increase is encouraging, because it means that more and more requesters are starting the hierarchical process of "resolving" a domain name into an IP address with an IPv6 communication to a root server. In a typical DNS deployment, the requesters are recursive name servers, acting on behalf of end-consumers that ultimately interact with the named resources. The increase reflects IPv6 adoption by recursive name servers and the networks they reach the root servers through. It doesn't necessarily mean that the named resource, the end-consumer, nor the networks they connect through support IPv6, though such transitions would be likely to follow, if not already in place.
It will be interesting to see what happens in the lead up to World IPv6 Launch on June 6. Verisign will share insights at www.VerisignLabs.com and we are very interested in gaining insights from the larger Internet community into questions such as: Will there be a significant acceleration in the various IPv6 adoption indicators? What are other observers seeing? With its open architecture, there is no single observation point for all impacts of IPv6 adoption and activity on the Internet. Assembling the larger picture will depend on the information shared by the Internet's many service providers and stakeholders.
As the current early adoption of this grand upgrade of network communications transitions into the mainstream, we can expect to see much larger percentages of domain names with IPv6-enabled name servers, of DNS queries received over IPv6, of requests for quad-A records, and ultimately broad adoption of IPv6 communications overall. Will 2012 be the year?
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