He didn't even know he was using IPv6!

I thought it would be good to have a non-technical entry today.

This morning, I received an email from a friend. He's a very technical guy with a home network for sharing media between several Macs. Last night, he went poking around with netstat and noticed that he was using IPv6 to connect to his file server. He was curious about "these strange looking IPv6 addresses," which, it turned out, were link-local addresses that his machines had self-assigned. All of his machines are Macs, so they are using Bonjour to find their peers on his network.

So I explained what had happened:

What's happened is that your machines are on the same network and are using Bonjour-enabled services. OS X's network stack will use IPv6 in preference to IPv4. Since it can use IPv6 to talk to you AFP server, it did. No harm done.

Note that your Macs won't (and can't) use IPv6 to connect to anything off your home network, since they don't have publicly routable IPv6 addresses.

I also pointed out that it wasn't just his home machines that have IPv6 enabled. His work machines have it enabled too. But again, they just have link-local addresses, so they're not hurting anything.

Ultimately, he wanted to know, "for a home network, is there really any advantage to using IPV6 or should I just disable all of it? "

Excellent question! I wanted to share my response with the group, in the hope that others find it useful.

For the immediate future, there's no harm either way. It's not hurting anything to leave IPv6 enabled. In fact, one could argue that it's working exactly as it should: Until you went snooping around, you didn't even notice that you were using IPv6 :) Everything still just worked. Alternatively, if you disable IPv6, you won't break anything.

IPv6 link-local addresses are mainly used for "network housekeeping" on v6-enabled networks. Bonjour can also use them to find servers on the subnet. But it can also use IPv4.