Apple leans further towards IPv6, wants to improve things
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July 13, 2015
With the latest beta release of iOS 9 and the already-patched El Capitan OS X 10.11, Apple is
leaning further towards IPv6 and wants to improve things.
In a blog post to the IETF's v6-ops mailing list, Apple CoreOS networking engineer David Schinazi
says the new release include a re-vamped version of the three-year-old Google-authored “Happy Eyeballs”
For the past two to three years, Apple has been a long-time supporter of IPv6, having first introduced
support for the protocol in 2006, but we now live in a dual-stack world.
Overall, Happy Eyeballs was designed to allow clients decide whether to use IPv4 or IPv6, depending
on which path to a server offered the best performance, mostly based on network latency.
A few adjustments to the implementation in the latest betas now favor IPv6 connections,
Schinazi said-- “Based on our testing, this makes our Happy Eyeballs implementation go from
roughly a 50/50 IPv4/IPv6 implementation in iOS 8 and Yosemite to ~99 percent IPv6 in iOS 9
and El Capitan betas.”
That's because “biasing towards IPv6 is now beneficial”, he added. With the still-slow-but-accelerating
mainstreaming of the new protocol, there aren't that many broken 'tunnels' anyway, and IPv6
performance may even be better on average, he added.
Naturally, it only works at all if the user has a connection that is somehow IPv6-capable.
Apple's original design first uses DNS to check the availability of a remote host over IPv6. Since
the idea is to have a bias in favor of IPv6, the Happy Eyeballs algorithm no longer defaults to the
first DNS response received.
Instead, if the first responder is IPv4, the algorithm sets a 25 ms timer to see if a response
comes back from an IPv6 host.
Of course, the network latency test is still there but with a 25 ms window-- “This algorithm uses
historical RTT data to prefer addresses that have a lower latency but has a 25 ms leeway-- if the historical
RTT of two compared addresses are within 25 ms of each other, we use RFC 3484 (IPv6 default address
selection) to choose the best one,” he said.
“If this behavior proves successful during the beta period, you should expect more IPv6 traffic
from Apple products in the future”, Schinazi concluded.
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