Static IPv6 addresses
Sat, 05 Dec 2020 22:00:48 +0000
Advent of Blog, day 5
Short one, today. After all that writing about airsonic and sniproxy the other day, I went to put some music on yesterday and found that it didn't work any more.
A series of suppositions
I broke my network significantly last week by switching from GNOME to KDE
... Let's just take a moment to reflect on how utterly bonkers it is that switching the desktop environment should break networking, but GNOME apparently has NetworkManager as a dependency, or possibly vice versa ...
and in the course of fixing that, I seem to have enabled systemd-networkd, which had changed the way that the machine was getting an IPv6 address. Where I previously had 2001:nnn:nnn:nnn::ed9, now I have 2001:nnn:nnn:nnn::148 and 2001:nnn:nnn:nnn:xxxx:xxxx:xxxx:xxxx.
IPv6 address allocation is simultaneously much simpler and much more complicated than IPv4 was, but the short form is: you can have a global address via SLAAC or via DHCPv6 or both. Addresses from SLAAC are 64 bits of prefix (here, 2001:nnn:nnn:nnn) plus 64 bits derived from your 48 bit MAC address. Addresses from DHCP are the prefix plus whatever the DHCP server gives you when you present it with a DUID, so I'm going to assume that these ::148 and ::ed9 are from DHCP - my MAC address isn't full of zeroes - and that networkd is presenting a different DUID than NetworkManager was.
There are, I guess, two possible routes to win here: find out how to
make networkd present the same DUID as NetworkManager did, or
reconfigure OpenWrt to accept the new one and give me the old
address. I'm going for the latter approach, so, let's login to the
router and use
uci show dhcp to find the per-host setting
dhcp.@host=host dhcp.@host.name='loaclhost' dhcp.@host.dns='1' dhcp.@host.hostid='0:0:0:e9d' dhcp.@host.leasetime='86400' dhcp.@host.ip='192.168.8.148' dhcp.@host.mac='fa:1e:9f:84:20:8e' dhcp.@host.duid='0000ab11406665c3f2e752320000'
There are two things I now know to be wrong with this:
- the duid in this configuration bears witness to my previous attempt
to fix this problem, but it doesn't actually match what is
networkctl status vbridge0on the client says
From DUID-EN/Vendor:0000ab11406665c3f2e752320000, the duid that OpenWrt sees is
00020000ab11406665c3f2e75232. I don't know of another way to check this than by looking in the Luci web interface, in the "Active DHCPv6 Leases" section
- the hostid is in the wrong format - I think OpenWrt doesn't like the colons
So we can fix them both:
uci set 'dhcp.@host.duid=00020000ab11406665c3f2e75232' uci set 'dhcp.@host.hostid=0e9d' /etc/init.d/odhcpd stop; /etc/init.d/odhcpd start
And down/up the interface on the client to make a new request (don't
renew, it doesn't help here)
sudo networkctl down vbridge0 ;sleep 1; sudo networkctl up vbridge0
and now I have my local services accessible again. Yay me.
You may be wondering why I have
vbridge0 as my primary interface on
that machine and not
and the answer is: it's a bridge between the ethernet interface and
one or more tap devices for virtual hosts. I don't think anything I've
described here would be different for a hardware ethernet, but don't
quote me, I haven't tried it.