IPv6 – MacOS Snow Leopard update

In this earlier post, I alluded to MacOS X Snow Leopard not supporting IPv6 out of the box. I mentioned that you needed these two commands to make IPv6 work:

# ip6 -a
# sysctl -w net.inet6.ip6.accept_rtadv=1

The first command was mentioned on a blog post as needed to “fully enable IPv6 features, beyond what is enabled via the Control Panel”. The second command enables the acceptance of IPv6 Router Advertisements.

This turns out to NOT be be needed at all. I did a complete new Snow Leopard install from the DVD this evening on a spare MacBook Pro, and everything IPv6 worked perfectly, out of the box. IPv6 was enabled by default, and fast visits to test-ipv6.com and ipv6-test.com showed full native IPv6 connectivity.

I can only surmise that somewhere along the way, my regular MacBook Pro had had IPv6 turned off in some unusual way. Or it could be that my original MacBook Pro was originally a Leopard install, which was upgraded to Snow Leopard.

So, MacOS X Snow Leopard completely IPv6 ready, out of the box. I’ll be testing Lion in January…


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  1. #1 by nomad on December 22, 2011 - 6:57 pm

    None of my Leopard or Snow Leopard boxes are properly getting IPv6 addresses from DHCPv6 & radvd. However, when I just had radvd running they did get auto-assigned addresses. I just tried the two commands you list here and … nothing changed. Darn.

  2. #2 by tomperrine on December 23, 2011 - 10:20 am

    I’m not doing DHCPv6 yet; all the home clients are using stateless auto-config addresses, and getting their default router via the router advertisements from the Airport.

    I can tell this because I see the clients pick up their auto-config address pretty much right away, but they don’t have a default IPv6 route until I see the first router advertisement go by (using tcpdump).

    You’re seeing exactly what I was seeing on my primary laptop, which was a Leopard->Snow Leopard upgrade, although those two commands did work for me (and had to be repeated after every reboot).

    Also, my primary laptop is also “managed” from OpenDirectory at work, which also complicated things.

    It wasn’t until I did the complete install (with disk wipe and reformat) on the secondary laptop with Snow Leopard that I saw MacOS “just work”. IPv6 was “known broken” in the first revs of Leopard, so even all the subsequent updates and upgrades may have left some broken IPv6 cruft around?

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