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[Launchpad Bug Tracker <1447715@xxxxxxxxxxxxxxxxxx>]

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(Original bug description follows SRU info)

[Description]

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]

None


-- original bug description --


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.

** Affects: ubuntu-translations
     Importance: Undecided
         Status: New

** Affects: ifupdown (Ubuntu)
     Importance: Medium
     Assignee: Dan Streetman (ddstreet)
         Status: Fix Released

** Affects: ifupdown (Ubuntu Precise)
     Importance: Medium
     Assignee: Dan Streetman (ddstreet)
         Status: Invalid

** Affects: ifupdown (Ubuntu Trusty)
     Importance: Medium
     Assignee: Dan Streetman (ddstreet)
         Status: Invalid

** Affects: ifupdown (Ubuntu Xenial)
     Importance: Medium
     Assignee: Dan Streetman (ddstreet)
         Status: In Progress


** Tags: patch sts-sru
-- 
dhclient -6: Can't bind to dhcp address: Cannot assign requested address
https://bugs.launchpad.net/bugs/1447715
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