IPv6: prelude in the key of radvd

Background knowledge: this post requires some knowledge of networking, at least to the point of knowing what IPv4 and IPv6 are, and what is meant by subnet notation like “/60” and “/64”.

I’ve just changed ISPs, because I wasn’t much of a fan of my old ISP’s demand that either we enter into a new 12 month contract before 27 November or they’d consider us re-contracted at that date. My new ISP is Internode, Australia’s favourite geek ISP, in part because they offer native IPv6 and it’s even supported by customer service. It took me an entire 24 hours to succumb to the temptation of wrecking my perfectly good home network by attempting to make it IPv4/IPv6 dual stack, partly motivated by Geoff Huston’s “the sky is falling” keynote at linux.conf.au 2011. I like doing my bit to hold up the sky.

I use a Linux machine as our router rather than a consumer router device, that is, my ADSL modem is set to bridge mode and we use our wireless router just as a switch; neither of them do routing. (Or shouldn’t, but we’ll get to that.) In terms of resources for doing this with Internode, or any other ISP who will advertise your IPv6 routes via DHCPv6, here’s some useful material:

• Internode’s own guide, which is a touch sketchy but gets the basics across
• Shane Short’s more extensive write-up of Internode and IPv6

The main problem I had is that for as yet unexplained reasons, while this radvd.conf stanza worked fine when my Linux server ran Ubuntu 11.04 with radvd 1.7, it doesn’t work on Ubuntu 11.10 with radvd 1.8:

prefix ::/64 {
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr on;
};


radvd 1.8 was advertising this in such a way as to get my Linux client to give this error (in /var/log/syslog):

IPv6 addrconf: prefix with wrong length 60

That is, it seems to have been advertising the entire /60 that Internode routes to each customer rather than a single /64. We ended up having to do something like this:

prefix 2001:db8:aaaa:bbbb::/64 {
AdvOnLink on;
AdvAutonomous on;
AdvRouterAddr on;
};

That is, because Internode’s IPv6 allocations are static, we just manually picked a /64 out of the /60 allocated to us, and advertised that. I’m not clear if this a bug or a change in the way radvd works or a mistake of mine, we never got a chance to find out because of a showstopper which you’ll see in the next, and at this stage, final post in my adventures in IPv6.