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

Dan Streetman dan.streetman+launchpad at canonical.com
Mon Nov 7 13:18:54 UTC 2016


update for this:

this patch is already included upstream in debian, and is already
included in yakkety.  It's not yet in xenial.  It's not required in
trusty (bug doesn't exist there).

additionally, bug 1633479 (which fixes this by putting the DAD wait in
isc-dhcp-client) is in proposed for p/t/x/y.  The root problem can be
fixed in either place (ifupdown via this bug, or isc-dhcp-client via
that bug), and doesn't need to be fixed in both.

So SRUing this to xenial will match the code that's upstream, and will
fix the bug for systems that don't have an updated isc-dhcp-client
(though I don't know why anyone would update ifupdown but not isc-dhcp-
client).  But, once bug 1633479 is moved from proposed to released in
xenial, this SRU isn't technically necessary, other than to keep
code/behavior similar between xenial and y+ ifupdown.

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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.

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