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 believed for a very brief time that I’d beaten IPv6 into shape but soon my husband started complaining that sometimes it worked, sometimes it didn’t, and basically questioning whether it was worth any more late nights. (I would poke things, we would jointly debug them, IPv6 involved us skipping dinner two nights in a row in the end.)
Basically what would happen was that anything we tried to connect to over IPv6, most noticeably Google itself (because they trust Internode’s IPv6 routing enough to have turned on IPv6 access for their customers) would either work or just hang. I vaguely suspected some kind of routing error.
Here’s something to try if you have mysterious intermittent IPv6 dropouts or hangs: watch the output of radvdump closely. What you are looking for is any router advertisements coming from a second source: rogue RAs was the search term I was using somewhat in vain.
Unfortunately, if you find such a thing, there are essentially two options (much as you do if someone has put a rogue DHCP server on a network). One is to remove the rogue device from the network, the other is to firewall its announcements away from your clients. Unfortunate in my case, that is, because it emerged that the source of the announcements was our D-Link wireless router (which, per the previous entry, we run as a switch). Removing a wireless switch from our network would have the unacceptable side-effect of re-introducing strings of blue cable to our home, and it’s pretty hard to firewall your switch itself. So in our case, the answer for the present time is to give up on home IPv6.
Overall, although the reason we gave up on IPv6 was not a Linux problem, I have to say that I was really surprised how immature Linux’s tools are at this point. The fundamentals exist: kernel support, DHCPv6 and stateless configuration servers and clients. As an IPv6 client, Linux is doing OK. If you connect a Linux machine to a network that happens to be using IPv6, it’ll likely Just Work. But at the tools and packaging level there’s still loads of gaps along the lines of:
- iptables and ip6tables are entirely separate programs, so you get to have your firewall configuration fun twice! (However, UFW handles this fairly nicely, if you’re in the market for a thin-ish wrapper around iptables.)
- configuring ppp for IPv6 is like ppp for IPv4 circa 1999 or 2000 or so. Things like the “oh yeah, for a reason no one knows, you won’t get a default route, so here’s a little script that will bring one up for you” (see Shane Short’s blog entry)
- radvd is a fairly crucial tool, but there aren’t a lot of example config files for different situations that I could find, and the man page assumes that you know a lot about router advertisements already
- if you want to use Ubuntu’s supported DHCP server (isc-dhcp-server) for DHCPv6, you need to write it a second init script and config file yourself
So after all that you might be tempted to use a dedicated router for IPv6 and I’d sympathise except that the D-Link device does it even worse than Linux. Not promising. I can’t see that moving many ADSL users over to IPv6 is going to happen any time soon.