dhclient on server install CD hangs forever trying to get an IPv6 lease

[Nick]

Attempting to install from the Ubuntu Server CD ISO ( http://mirror.bytemark.co.uk/ubuntu-releases/11.10/ubuntu-11.10-server-amd64.iso ) on a Bytemark (BigV) virtual machine, dhclient waits forever trying to get an IPv6 lease.

I'm not sure if our network can be more helpful in terms of allowing the IPv6 lease to be gotten (at the moment, we don't run a DHCPv6 server at all, and RAs are lacking), but the current behaviour is surely a bug.

The installer is hung on running:

[9316] udpkg --configure --force-configure netcfg
[9317] netcfg
[9354] dhclient -6 -S -cf /var/lib/netcfg/dhclient6.conf -s

The screen on Alt+F1 is just a plain blue, with no information about what's happening. On Alt+F4, I see the following:

dhclient: XMT: Info-Request on eth0, interval 930ms
dhclient: XMT: Info-Request on eth0, interval 1800ms
dhclient: XMT: Info-Request on eth0, interval 3510ms
dhclient: XMT: Info-Request on eth0, interval 7250ms
dhclient: XMT: Info-Request on eth0, interval 14940ms
dhclient: XMT: Info-Request on eth0, interval 30240ms
dhclient: XMT: Info-Request on eth0, interval 63100ms
dhclient: XMT: Info-Request on eth0, interval 125080ms
dhclient: XMT: Info-Request on eth0, interval 124300ms
[at this point, I ran kill 9354]

Given that there simply isn't a DHCPv6 server running on the network, this level of persistence is wrong. Once I killed the process, I installed from IPv4 without any further issues.

Prior to the dhclient attempt, there was an attempt to use rdisc6. This discovered a router, and was given what it considered to be an invalid prefix (we assign a /56 per VLAN, which is advertised, and assign each machine within that VLAN a /64, but currently it needs to be manually configured by the user). Those routes all ended up in the route table.

Suggested fix: fail and fall back to IPv4 after 4 attempts or so? man dhclient.conf suggests the default timeout is 300 seconds - five minutes - which is an awfully long time to be looking at a blank screen. However, I waited for ~350 seconds and it didn't seem to timeout itself automatically, so maybe the default is different in -6 mode, or perhaps it needs setting explicitly and the manpage is wrong.

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.