So I'm not convinced that doing this in dhclient is necessarily right.
Unlike IPv4 where DHCP operates over a raw socket, in IPv6 mode,
dhclient is just a regular network client and as such requires a source
address to be set so it can contact the network (the link-local address
in this case).
As dhclient is supposed to only be triggered after a RA has been
received and parsed, it should be the job of whatever handles the RA to
wait until a viable link-local has been established before triggering
That being said, since we don't seem to have anything that handles that
first configuration step properly, this workaround certainly won't hurt
and will fix the current race condition.
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dhclient does not wait for ipv6 dad (duplicate address detection)
Status in isc-dhcp package in Ubuntu:
dhclient -6 does not wait for an interface go through duplicate address
As a result the following will almost always fail:
$ ip link set down dev $dev
$ dhclient -6 -1 -v eth0
Internet Systems Consortium DHCP Client 4.3.3
Copyright 2004-2015 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/
Can't bind to dhcp address: Cannot assign requested address
Please make sure there is no other dhcp server
running and that there's no entry for dhcp or
bootp in /etc/inetd.conf. Also make sure you
are not running HP JetAdmin software, which
includes a bootp server.
If you think you have received this message due to a bug rather
than a configuration issue please read the section on submitting
bugs on either our web page at www.isc.org or in the README file
before submitting a bug. These pages explain the proper
process and the information we find helpful for debugging..
$ echo $?
* bug 1447715: dhclient -6: Can't bind to dhcp address: Cannot assign
* bug 1633562: 'dhclient -6 -S' does not bring interface up
DistroRelease: Ubuntu 16.10
Package: isc-dhcp-client 4.3.3-5ubuntu15
ProcVersionSignature: Ubuntu 4.8.0-22.24-generic 4.8.0
Uname: Linux 4.8.0-22-generic x86_64
NonfreeKernelModules: zfs zunicode zcommon znvpair zavl
Date: Fri Oct 14 09:18:52 2016
InstallationDate: Installed on 2015-07-23 (449 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Alpha amd64 (20150722.1)
UpgradeStatus: No upgrade log present (probably fresh install)
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