[Bug 1447715] Re: dhclient -6: Can't bind to dhcp address: Cannot assign requested address

[Dan Streetman]

for NetworkManager, this is fixed starting in wily (see comment 13) and
so should work in xenial/yakkety; and in trusty, dhclient still works
(per description stating dhclient works in isc-dhcp-client
4.2.4-7ubuntu14).  I'm not sure if NetworkManager using dhcpv6 works in
precise (but who is using precise with NetworkManager?).  It would be
useful if anyone could test NetworkManager on precise using dhcpv6.

for ifupdown/dhclient, as scott said in bug 1633479 comment 13, in older
trusty/precise dhclient, it actually retries and so the bug doesn't
exist there.  In yakkety, this is already fixed in ifupdown (via fix
included in debian ifupdown pulled into yakkety).  So this bug only is
possibly applicable in xenial; and I just confirmed that by updating
only isc-dhcp-client to version 4.3.3-5ubuntu12.4, it does succeed in
getting a dhcpv6 address.

So no, it doesn't seem that this patch to ifupdown is needed in xenial,
and if applied I don't think there would be any noticable difference.
So it should be fine to mark this Won't Fix for xenial, as it was fixed
in isc-dhcp-client via bug 1633479.

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Title:
  dhclient -6: Can't bind to dhcp address: Cannot assign requested
  address

Status in ifupdown package in Ubuntu:
  Fix Released
Status in ifupdown source package in Xenial:
  In Progress
Status in ifupdown package in Debian:
  Fix Released

Bug description:
  [Impact]

  When using dhcpv6 configured via ifupdown, the interface's dhcp client
  fails to start at boot with the error:

  Can't bind to dhcp address: Cannot assign requested address

  This is because ifupdown doesn't wait, after bringing the interface
  up, for it to complete its link-local Duplicate Address Detection
  (DAD), and the dhcp client can't bind to the link-local address
  because it's still in "tentative" state (until DAD completes).

  This is fixed upstream in debian ifupdown in version 0.8.11 by adding
  '-tentative' to the /lib/ifupdown/wait-for-ll6.sh script; before the
  script was only waiting for the link-local address to appear, now it
  waits until the link-local address appears and is not in 'tentative'
  state.

  [Test Case]

  Configure an interface, using ifupdown, with dhcpv6 (e.g. iface eth0
  inet6 dhcp) and reboot. It will fail to get a dhcp address during
  boot.

  [Regression Potential]

  None

  [Other Info]

  After upgrading to Ubuntu 15.04 my computer is unable to obtain an
  IPv6 address via DHCPv6. The root cause is that dhclient is exiting
  with the following message:

  -----------------------------------------------------
  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..

  exiting.
  -----------------------------------------------------

  The problem seems to exist in isc-dhcp-client 4.3.1-5ubuntu2 (15.04
  version) because downgrading to isc-dhcp-client 4.2.4-7ubuntu14 (14.10
  version) allows me to obtain an address.

  NetworkManager is the one launching dhclient. The two invocations (one
  for IPv4 and one for IPv6) are:

  dhclient_start(): running: /sbin/dhclient -d -q -sf
  /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/sendsigs.omit.d
  /network-manager.dhclient-eth0.pid -lf /var/lib/NetworkManager
  /dhclient-c0a3dfde-5c0b-4cef-9c3b-563cfb1fb9d2-eth0.lease -cf
  /var/lib/NetworkManager/dhclient-eth0.conf eth0

  dhclient_start(): running: /sbin/dhclient -d -q -6 -N -sf
  /usr/lib/NetworkManager/nm-dhcp-helper -pf /run/sendsigs.omit.d
  /network-manager.dhclient6-eth0.pid -lf
  /var/lib/NetworkManager/dhclient6-c0a3dfde-5c0b-4cef-9c3b-
  563cfb1fb9d2-eth0.lease -cf
  /var/lib/NetworkManager/dhclient6-eth0.conf eth0

  I do not see anything suspicious with the way both dhclients are
  invoked.

  Given that a downgrade allows me to obtain an IPv6 address I think
  this might be a bug in the ISC DHCP client rather than in
  NetworkManager.

  Related Bugs:
   * bug 1633479: dhclient does not wait for ipv6 dad (duplicate address detection)

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