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DNS infrastructure sprinting to IPv6 while users lag

More than one third of queries hit v6-capable servers, says 'net boffin Huston

IPv6 might be moving slowly among the general community, but it's penetrating the Internet infrastructure at a much higher rate.

In an article published at his Potaroo blog, Internet address Registry for the Asia Pacific region chief scientist Geoff Huston has published the results of a study into how many servers in the Domain Name System (DNS) support IPv6 – and it seems to be good news: “there is a lot of IPv6 in the DNS, perhaps more than we anticipated,” he says.

To get a handle on the capabilities of DNS resolvers around the world, Huston oversaw a three-month measurement experiment “serving between five million and 10 million experiments per day through an online advertisement campaign, resulting in some 400 million individual experiments.”

The analysis suggests 35 per cent of Internet users have their DNS queries handled by IPv6-capable resolvers – even though only seven per cent of users are on IPv6.

Digging such numbers out of the 'net is harder than you might expect. For example (unsurprisingly), one reason for this is that DNS queries are skewed towards a small number of the largest services – Google fields nearly 32 per cent of all queries, followed by AT&T (13.5 per cent), Comcast (11.5 per cent) and OpenDNS (3.4 per cent).

By the time you get to 25th on the list, you're looking at a resolver that handles a mere 0.4 per cent of queries. That's an interesting side observation in the research, because the whole experiment observed more than 345,000 unique resolvers.

While there's a lot of IPv6 in the DNS, Huston still notes that for individual sysadmins, making the switch in DNS servers under their control requires “considerable care and attention to detail”.

The paper states: “We still see a significant level of IPv6 Path MTU black holes, so it makes some sense to clamp the TCP MSS down to 1220 on IPv6 TCP servers to try to avoid this problem in the first place. At the same time, we also see a significant level of IPv6 extension header packet drop, and in a previous experiment we observed a 30 per cent drop rate for fragmented IPv6 DNS responses.”

“The DNS is well on the path of transition and perhaps further along this path than all the other elements of the Internet’s infrastructure”, the post concludes. ®

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