Apple's IPv6 fix favours IPv4 -

While the rest of the world waits for the internet to move to IPv6, Apple appears to have made a leap backwards with its latest Snow Leopard patch.

For a while, Jobs' Mob has been at the forefront of helping the world move to IPv6. In Mac OS X 10.2 Jaguar, Apple introduced IPv6 support which preferred IPv6 over IPv4 if it has a choice. It used something called 6to4 technology which sticks IPv6 packets inside IPv4 packets. 

It means that users of ISPs that don't support IPv6 yet can still connect to the IPv6 Internet.

But according to Ars Technica, yesterday's 10.6.5 Snow Leopard update turned that all upside down.

Snow Leopard will still try to connect over IPv6 first, but for IPv6 destinations, Leopard will now opt for IPv4 instead. It will only connect over 6to4 to IPv6 destinations if there's no IPv4.

Apple's argument is that 6to4 technology is responsible for a disproportionate share of non-working IPv6 setups. If you give Google an IPv6 address 0.1 percent of all users would be unable to connect to the search giant.

For those who came in late, 6to4 is an automatic tunnelling mechanism where IPv6 packets are put inside IPv4 packets so users of ISPs that don't support IPv6 yet can still connect to the IPv6 Internet.

It is all fully automatic but one of its problems is that if it breaks it implodes. 6to4 gateways can be flakey and some ISPs don't carry the 6to4 route in their network, while many universities filter 6to4 packets.

Vista and 7 systems always enable 6to4 automatically if they have a public IPv4 address. Windows will try to use 6to4 to other 6to4 users but IPv4 if the choice is between IPv4 and 6to4.

But Apple's change means that it's no longer possible to turn on 6to4 and experiment. 6to4 functionality in the Airport Extreme base stations is now rendered useless.

Since few ISPs offer IPv6 connectivity to consumers, the only alternatives are non-automatic tunnels.

It seems that Apple has decided that it is better to ignore transition technology and wait for an IPv6 world. Which is is incredibly late in coming. [That's enough IP stuff. Ed.]