Network engineers from Yahoo are pitching what they admit is a "really ugly hack" to the Internet's Domain Name System, but they say it is necessary for the popular Web content provider to support IPv6, the long-anticipated upgrade to the Internet's main communications protocol. Yahoo outlined its proposal for changes to DNS recursive name resolvers at a meeting of the Internet Engineering Task Force (IETF) held this week.

Yahoo says it needs a major change to the DNS, which matches IP addresses with corresponding domain names, in order to provide IPv6 service without inadvertently cutting off access to hundreds of thousands of visitors. Under Yahoo's proposal, these visitors would continue accessing content via IPv4, the current version of the Internet Protocol.

The reason Yahoo is seeking this change to the DNS is that a significant percentage of Internet users have broken IPv6 connectivity. Web content providers say they need mechanisms to discover that a user's IPv6 connectivity is broken and to switch these users to IPv4 on the fly. Yahoo views DNS as the best place to make this switch.

"If you roll out IPv6, you will break 0.078% of users. That sounds negligible, but for Yahoo that's taking 470,000 users offline," says Igor Gashinsky, a senior network architect at Yahoo. Gashinsky presented Yahoo's DNS recursive name resolver proposal to the IETF's DNS Operations Working group.

Gashinsky says problems occur when "the user has a broken home gateway, or a broken firewall or his web browser has a timeout that's between 21 and 186 seconds, which we consider to be broken. That's a lot of breakage, and that is a very big barrier for content providers to support IPv6." Gashinsky says the estimate that 0.078% of users have broken IPv6 connectivity comes from Google, which has been aggressively moving its services to IPv6, including YouTube, Search, Mail and Maps.

Gashinsky adds that Yahoo is conducting its own analysis of broken IPv6 connectivity, which it will share with the Internet engineering community in June. Yahoo has started IPv6 peering around the world with various ISPs, and a company spokesman says it will begin serving up web pages to IPv6 users "as soon as possible."  

"I should not be breaking any IPv4 user if I enable IPv6," Gashinsky says, explaining why he needs this change to the DNS. Yahoo's revelation that turning on IPv6 will result in hundreds of thousands of its visitors being unable to access its content is significant because the Internet engineering community is pressuring website operators to support IPv6.