dhclient-script fails to wait for link-local address

[Jeff]

[impact]

bug 1633479 made a change to isc-dhcp to wait for an interface's link-local ipv6 address to switch from 'tentative' to normal, because all link-local addresses briefly go through a 'tentative' state while the kernel is performing ipv6 link-local 'duplicate address detection' (DAD). While in the 'tentative' state, dhclient can't take over the interface and send out
dhcpv6 requests; it must wait until DAD completes.

However, the change made in that bug does not account for the case where the 'tentative' check is done before the interface has even set up a link-local address; its case statement assumes if there is no 'tentative' or 'dadfailed' string in the output, the link-local address is ready to use. When the address check finds no address at all, this will return as successful, even though it shouldn't, and dhclient will fail to get the dhcpv6 address.

[test case]

on a system that is configured for dhcpv6 on one or more of its interfaces, repeatedly try to get the dhcpv6 address. For interfaces that are slower to actually set up their initial tentative link-local address, they will occasionally fail, since the current code is a race between the kernel adding the tentative link-local address, and the dhclient-script.linux code checking the interface for a tentative address.

with the patch to correct this, even interfaces slow to add their tentative link-local address should correctly wait for the address to get added, and then transition from tentative to normal, and then begin the dhcpv6 process.

[regression potential]

errors in this function can cause dhclient to fail to get a ipv6 address for an interface; regression would happen if this patch makes it fail more than it already is failing, but would not cause other failures or problems after getting an ipv6 address; this patch will affect only startup-time.

additionally, the current behavior of dhclient when using an interface that has no link-local address after being brought up is to exit immediately; while after this patch dhclient will wait ~6 seconds before exiting (while waiting for the interface to get a non-tentative link-local addr). This is the point of this bug, that some NIC hw doesn't show a tentative link-local addr immediately after coming up. However, if dhclient -6 is configured to run on an interface without any link state at all (e.g. its physical cable is unplugged), then while before dhclient would exit immediately with error, it now waits 6 seconds. If the system is misconfigured like that, or if someone pulls a cable and reboots, then system boot will be delayed an extra 6 seconds. However, that short delay for misconfigured/broken systems seems acceptable to me, in exchange for allowing dhclient to work with slightly slow NIC hw. Additionally, consider that if the problem is instead no dhcpv6 server, dhclient -6 will wait a much, much longer amount of time for a dhcpv6 response before giving up.

[other info]

related bug 1633479

[original description]

Summary:
========

If a interface does not yet have a link-local address (as it may have just been brought up), dhclient -6 <ifname> will fail. The built-in "wait for link-local address" loop does not function properly, causing DHCP failure.

Discussion:
===========

In trying to configure isc-dhcp-client 4.3.5-3ubuntu1 for IPv6 on Ubuntu 17.04, I was finding that on boot I was getting failures with the logged message "no link-local IPv6 address for <ifname>"

I found that it took several seconds for the link-local address to be assigned when the interface came up (in this case, the ISP/modem-facing interface), and worked around it with a script that looks at

  /sbin/ifconfig $IFACE | /bin/fgrep -q 'scopeid 0x20'

and loops for a fixed number of times for that to be successful.

On looking at /sbin/dhclient-script it appears that it *tries* to do the same thing in

  # set the link up and wait for ipv6 link local dad to finish
  ipv6_link_up_and_dad()

this code sets

  out=$(ip -6 -o address show dev "$dev" scope link)

then checks it with a case statement inside of a loop for

        case " $out " in
            *\ dadfailed\ *)
                error "$dev: ipv6 dad failed."
                return 1;;
            *\ tentative\ *) :;;
            *) return 0;;
        esac

If there is no link-local address, $out will be empty. The default case is taken, and the loop exits immediately:

$ echo "'$out'" ; case " $out " in
> *\ dadfailed\ *)
> echo "dadfailed"
> ;;
> *\ tentative\ *)
> echo "tentative"
> ;;
> *)
> echo "default"
> esac
''
default

As a result, there is no "wait for link-local address" and when there is no link-local address, dhclient fails later on.

Possible Fix:
=============

Adding "the missing case" for "no address" case that continues the loop is one possible solution.

.        case " $out " in
.            *\ dadfailed\ *)
.                error "$dev: ipv6 dad failed."
.                return 1;;
.            *\ tentative\ *) :;;
+      " ")
+    :
+    ;;
.            *) return 0;;
.        esac

At least in my situation, this prevents the failure of dhclient due to the link-local address not being "ready" yet.

[Jeff (jeffsf)]

Confirmed that the same apparent flaw in dhclient-script appears to exist in 4.3.3-5ubuntu12.7 under Ubuntu 16.04.3 LTS

This appears related to / caused by LP: #1633479
based on http://launchpadlibrarian.net/291516262/isc-dhcp_4.3.3-5ubuntu15_4.3.3-5ubuntu15.1.diff.gz

[Jeff (jeffsf)]

Confirmed to resolve issue seen here.

I won't be concerned if you prefer alternate sh-script formatting over mine.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "Patch to detect no link-local address" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Dan Streetman (ddstreet)]

Hi Jeff,

Thanks for reporting and debugging this!

I've tweaked your patch from comment 2 slightly, you can see my version in the debdiffs attached. I was concerned that just a " " check may not always work right, so I explicitly check for the ip output to contain 'inet6' (but not 'tentative') which is really what the function is supposed to be doing.

Since this needs to go into the development release, the SRUs to older releases have to wait. And since artful is currently in freeze, this will need to wait for the b-series development to start before we can add the fix, and then SRU the fixes back to artful and older. I'll come back to this once b-series development has started and get the process rolling.

Until then, I built test packages here:
https://launchpad.net/~ddstreet/+archive/ubuntu/lp1718568

can you verify that fixes it on your system?

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.3.5-3ubuntu4

---------------
isc-dhcp (4.3.5-3ubuntu4) bionic; urgency=medium

  * dhclient-script.linux: handle empty case also when waiting for ipv6 link
    local DAD. (LP: #1718568)

 -- Dan Streetman <email address hidden> Thu, 12 Oct 2017 08:48:06 -0400

[Łukasz Zemczak (sil2100)]

I will be accepting this, but I'm a bit worried about the test case here as it relies on a race-related occasional failure and it might be hard to test reliably. Is there no other more reliable way to reproduce the case that's being fixed here, e.g. to delay the initial tentative link-local address assignment? Probably not?

[Łukasz Zemczak (sil2100)]

Hello Jeff, or anyone else affected,

Accepted isc-dhcp into artful-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.3.5-3ubuntu2.1 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-artful to verification-done-artful. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-artful. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Łukasz Zemczak (sil2100)]

Hello Jeff, or anyone else affected,

Accepted isc-dhcp into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.3.3-5ubuntu12.8 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Łukasz Zemczak (sil2100)]

Hello Jeff, or anyone else affected,

Accepted isc-dhcp into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.2.4-7ubuntu12.11 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-trusty to verification-done-trusty. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-trusty. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Marc Deslauriers (mdeslaur)]

Unfortunately, this SRU was superseded by a security update.

New debdiffs need to be prepared on top of the security updates.

[Dan Streetman (ddstreet)]

ok i'll recreate the debdiffs and reupload.

[Dan Streetman (ddstreet)]

> Is there no other more reliable way to reproduce the case that's being fixed here

sure yes, here's what i did; first, setup:

-create VMs for the releases (T/X/A), managed by virsh (e.g. with uvt-kvm or whatever)
-add a second interface to each of them, e.g.:

$ virsh attach-interface lp1718568-artful network default --model virtio --persistent

-set up another server/vm/container/whatever, connected to the same network as the test VM second interfaces, and install and configure isc-dhcp-server (or dnsmasq or whatever dhcpv6 server) on that to serve out dhcpv6

now on each release VM:

-check the virsh interface you'll be using, e.g.:

$ virsh domiflist lp1718568-artful
Interface Type Source Model MAC
-------------------------------------------------------
vnet3 network default virtio 52:54:00:3f:b9:ad
vnet0 network default virtio 52:54:00:bf:16:8a

confirm which matches the test interface in the VM using mac; in my case it's vnet0. now, bring its link state down using virsh:

$ virsh domif-setlink lp1718568-artful vnet0 down

and ssh into the test VM (on its first, still working, default interface - or use virt-viewer or whatever) and test dhclient -6, making sure to first verify the test interface is down (i.e. that it doesn't already have a link-local addr):

ubuntu@lp1718568-artful:~$ sudo ip a show ens7
3: ens7: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 52:54:00:bf:16:8a brd ff:ff:ff:ff:ff:ff

ubuntu@lp1718568-artful:~$ sudo dhclient -v -6 ens7
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

no link-local IPv6 address for ens7

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.

as expected (for this bug), that fails immediately. now, upgrade to the test version in my ppa
https://launchpad.net/~ddstreet/+archive/ubuntu/lp1718568

ubuntu@lp1718568-artful:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.3.5-3ubuntu2.2+hf1718568v20180302b1 amd64 DHCP client for automatically obtaining an IP address
ii isc-dhcp-common 4.3.5-3ubuntu2.2+hf1718568v20180302b1 amd64 common manpages relevant to all of the isc-dhcp packages

again, make sure the interface is down (no link-local addr) and try the new dhclient:

ubuntu@lp1718568-artful:~$ sudo ip l set down dev ens7
ubuntu@lp1718568-artful:~$ sudo ip a show ens7
3: ens7: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether 52:54:00:bf:16:8a brd ff:ff:ff:ff:ff:ff

ubuntu@lp1718568-artful:~$ sudo dhclient -v -6 ens7
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/softw...

[Łukasz Zemczak (sil2100)]

Hello Jeff, or anyone else affected,

Accepted isc-dhcp into artful-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.3.5-3ubuntu2.3 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-artful to verification-done-artful. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-artful. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Łukasz Zemczak (sil2100)]

Hello Jeff, or anyone else affected,

Accepted isc-dhcp into xenial-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.3.3-5ubuntu12.10 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-xenial to verification-done-xenial. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-xenial. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Łukasz Zemczak (sil2100)]

Hello Jeff, or anyone else affected,

Accepted isc-dhcp into trusty-proposed. The package will build now and be available at https://launchpad.net/ubuntu/+source/isc-dhcp/4.2.4-7ubuntu12.13 in a few hours, and then in the -proposed repository.

Please help us by testing this new package. See https://wiki.ubuntu.com/Testing/EnableProposed for documentation on how to enable and use -proposed.Your feedback will aid us getting this update out to other Ubuntu users.

If this package fixes the bug for you, please add a comment to this bug, mentioning the version of the package you tested and change the tag from verification-needed-trusty to verification-done-trusty. If it does not fix the bug for you, please add a comment stating that, and change the tag to verification-failed-trusty. In either case, without details of your testing we will not be able to proceed.

Further information regarding the verification process can be found at https://wiki.ubuntu.com/QATeam/PerformingSRUVerification . Thank you in advance!

[Dan Streetman (ddstreet)]

artful:

ubuntu@lp1718568-artful:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.3.5-3ubuntu2.2 amd64 DHCP client for automatically obtaining an IP address
ii isc-dhcp-common 4.3.5-3ubuntu2.2 amd64 common manpages relevant to all of the isc-dhcp packages

ubuntu@lp1718568-artful:~$ sudo ip l set down dev ens7
ubuntu@lp1718568-artful:~$ sudo ip l show ens7
3: ens7: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:bf:16:8a brd ff:ff:ff:ff:ff:ff

(on host):
$ virsh domif-setlink lp1718568-artful vnet8 down
Device updated successfully

(back on guest):
ubuntu@lp1718568-artful:~$ sudo dhclient -v -6 ens7
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

no link-local IPv6 address for ens7

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.

after updating to -proposed:

ubuntu@lp1718568-artful:~$ sudo ip l set down dev ens7
ubuntu@lp1718568-artful:~$ sudo ip l show ens7
3: ens7: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:bf:16:8a brd ff:ff:ff:ff:ff:ff
ubuntu@lp1718568-artful:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.3.5-3ubuntu2.3 amd64 DHCP client for automatically obtaining an IP address
ii isc-dhcp-common 4.3.5-3ubuntu2.3 amd64 common manpages relevant to all of the isc-dhcp packages

ubuntu@lp1718568-artful:~$ sudo dhclient -v -6 ens7
Internet Systems Consortium DHCP Client 4.3.5
Copyright 2004-2016 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

(blocks, waiting for ipv6 link-local addr)

(on host):
$ virsh domif-setlink lp1718568-artful vnet8 up
Device updated successfully

(back on guest):
Listening on Socket/ens7
Sending on Socket/ens7
PRC: Soliciting for leases (INIT).
XMT: Forming Solicit, 0 ms elapsed.
XMT: X-- IA_NA 00:bf:16:8a
XMT: | X-- Request renew in +3600
XMT: | X-- Request rebind in +5400
XMT: | X-- Request address 2001:db8::99.
XMT: | | X-- Request preferred in +7200
XMT: | | X-- Request valid in +10800
XMT: Solicit on ens7, interval 1020ms.
RCV: Advertise message on ens7 from fe80::5054:ff:fec9:897c.
RCV: X-- IA_NA 00:bf:16:8a
RCV: | X-- starts 1520535276
RCV: | X-- t1 - renew +3600
RCV: | X-- t2 - rebind +7200
RCV: | X-- [Options]
RCV: | | X-- IAADDR 2001:db8::99
RCV: | | | X-- Preferred lifetime 604800.
RCV: | | | X-- Max lifetime 2592000.
RCV: X-- Server ID: 00:01:00:01:22:2c:61:12:52:54:00:c9:89:7c
RCV: Advertisement recorded.
PRC: Selecting best adver...

[Dan Streetman (ddstreet)]

xenial:

ubuntu@lp1718568-xenial:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.3.3-5ubuntu12.9 amd64 DHCP client for automatically obtaining an IP address
ii isc-dhcp-common 4.3.3-5ubuntu12.9 amd64 common files used by all of the isc-dhcp packages

host$ virsh domif-setlink lp1718568-xenial vnet6 down
Device updated successfully

ubuntu@lp1718568-xenial:~$ sudo dhclient -v -6 ens7
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/

no link-local IPv6 address for ens7

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.

with -proposed pkg:

ubuntu@lp1718568-xenial:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.3.3-5ubuntu12.10 amd64 DHCP client for automatically obtaining an IP address
ii isc-dhcp-common 4.3.3-5ubuntu12.10 amd64 common files used by all of the isc-dhcp packages
ubuntu@lp1718568-xenial:~$ sudo ip l set down dev ens7
ubuntu@lp1718568-xenial:~$ sudo ip l show dev ens7
3: ens7: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:f3:99:a8 brd ff:ff:ff:ff:ff:ff

ubuntu@lp1718568-xenial:~$ sudo dhclient -v -6 ens7
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/

(blocks)

$ virsh domif-setlink lp1718568-xenial vnet6 up
Device updated successfully

Listening on Socket/ens7
Sending on Socket/ens7
Created duid \000\001\000\001\"4D\337RT\000\363\231\250.
PRC: Soliciting for leases (INIT).
XMT: Forming Solicit, 0 ms elapsed.
XMT: X-- IA_NA 00:f3:99:a8
XMT: | X-- Request renew in +3600
XMT: | X-- Request rebind in +5400
XMT: Solicit on ens7, interval 1040ms.
RCV: Advertise message on ens7 from fe80::5054:ff:fec9:897c.
RCV: X-- IA_NA 00:f3:99:a8
RCV: | X-- starts 1520535647
RCV: | X-- t1 - renew +3600
RCV: | X-- t2 - rebind +7200
RCV: | X-- [Options]
RCV: | | X-- IAADDR 2001:db8::98
RCV: | | | X-- Preferred lifetime 604800.
RCV: | | | X-- Max lifetime 2592000.
RCV: X-- Server ID: 00:01:00:01:22:2c:61:12:52:54:00:c9:89:7c
RCV: Advertisement recorded.
PRC: Selecting best advertised lease.
PRC: Considering best lease.
PRC: X-- Initial candidate 00:01:00:01:22:2c:61:12:52:54:00:c9:89:7c (s: 155, p: 0).
XMT: Forming Request, 0 ms elapsed.
XMT: X-- IA_NA 00:f3:99:a8
XMT: | X-- Requested renew +3600
XMT: | X-- Requested rebind +5400
XMT: | | X-- IAADDR 2001:db8::98
XMT: | | | X-- Preferred lifetime +7200
XMT: | | | X-- Max lifetime +7500
XMT: V IA_NA appended.
XMT: Request on ens7, interval 990ms.
RCV: Reply message on ens7 from fe80::5054:ff:fec9...

[Dan Streetman (ddstreet)]

trusty:

host~$ virsh domif-setlink lp1718568-trusty vnet4 down
Device updated successfully

ubuntu@lp1718568-trusty:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.2.4-7ubuntu12.12 amd64 ISC DHCP client
ii isc-dhcp-common 4.2.4-7ubuntu12.12 amd64 common files used by all the isc-dhcp* packages
ubuntu@lp1718568-trusty:~$ sudo ip l set down dev eth1
ubuntu@lp1718568-trusty:~$ sudo ip l show eth1
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:1f:1a:c6 brd ff:ff:ff:ff:ff:ff

ubuntu@lp1718568-trusty:~$ sudo dhclient -v -6 eth1
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

no link-local IPv6 address for eth1

with -updates pkg:

ubuntu@lp1718568-trusty:~$ dpkg -l | grep isc-dhcp
ii isc-dhcp-client 4.2.4-7ubuntu12.13 amd64 ISC DHCP client
ii isc-dhcp-common 4.2.4-7ubuntu12.13 amd64 common files used by all the isc-dhcp* packages
ubuntu@lp1718568-trusty:~$ sudo ip l set down dev eth1
ubuntu@lp1718568-trusty:~$ sudo ip l show eth1
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN mode DEFAULT group default qlen 1000
    link/ether 52:54:00:1f:1a:c6 brd ff:ff:ff:ff:ff:ff

ubuntu@lp1718568-trusty:~$ sudo dhclient -v -6 eth1
Internet Systems Consortium DHCP Client 4.2.4
Copyright 2004-2012 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

(blocks)

host$ virsh domif-setlink lp1718568-trusty vnet4 up
Device updated successfully

Listening on Socket/eth1
Sending on Socket/eth1
PRC: Soliciting for leases (INIT).
XMT: Forming Solicit, 0 ms elapsed.
XMT: X-- IA_NA 00:1f:1a:c6
XMT: | X-- Request renew in +3600
XMT: | X-- Request rebind in +5400
XMT: Solicit on eth1, interval 1010ms.
RCV: Advertise message on eth1 from fe80::5054:ff:fec9:897c.
RCV: X-- IA_NA 00:1f:1a:c6
RCV: | X-- starts 1520536242
RCV: | X-- t1 - renew +3600
RCV: | X-- t2 - rebind +7200
RCV: | X-- [Options]
RCV: | | X-- IAADDR 2001:db8::93
RCV: | | | X-- Preferred lifetime 604800.
RCV: | | | X-- Max lifetime 2592000.
RCV: X-- Server ID: 00:01:00:01:22:2c:61:12:52:54:00:c9:89:7c
RCV: Advertisement recorded.
PRC: Selecting best advertised lease.
PRC: Considering best lease.
PRC: X-- Initial candidate 00:01:00:01:22:2c:61:12:52:54:00:c9:89:7c (s: 155, p: 0).
XMT: Forming Request, 0 ms elapsed.
XMT: X-- IA_NA 00:1f:1a:c6
XMT: | X-- Requested renew +3600
XMT: | X-- Requested rebind +5400
XMT: | | X-- IAADDR 2001:db8::93
XMT: | | | X-- Preferred lifetime +7200
XMT: | | | X-- Max lifetime +7500
XMT: V IA_NA appended.
XMT: Request on eth1, interval 1040ms.
RCV: Reply message on eth1 from fe80::5054:ff:fec9:897c.
RCV: X-- IA_NA 00:1f:1a:c6
RCV: | X-- starts 1520536243
RCV: | X-- t1 - renew +3600
RCV: | X-- t2 - rebind +7200
RCV: | X-- [Options]
RCV: | | X-- IAADDR 2001:db8::93
RCV: | | | X-- Prefer...

[Łukasz Zemczak (sil2100)]

Hey Dan! I see some autopkgtests failing for this upload for artful, I re-ran them to see how frequently those are reproducible. The systemd one is flaky, but I would like someone to take a look at the network-manager ones.

[Dan Streetman (ddstreet)]

The only failure shown now seems to be network-manager, which is failing its 'test_no_ap' test; that appears to have been failing for a while:
http://autopkgtest.ubuntu.com/packages/n/network-manager/artful/amd64

also there's a bug opened today for it:
https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1755466

The test log in that bug description shows the same failure, test_no_ap, and the log shows the isc-dhcp installed package version is 4.3.5-3ubuntu2.2, which doesn't contain the change from this bug.

The other autopkgtest it's failing is the 'killswitches-no-urfkill' test; it fails at this check:

if ! LC_MESSAGES=C nmcli radio wifi | grep -qc disabled; then
        echo "ERROR: NM could not track device state."

This is failing because the test case is faulty; it's being tracked in this bug:
https://bugs.launchpad.net/ubuntu/+source/network-manager/+bug/1733321

So I think we can ignore both these autopkgtest failures.

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.3.5-3ubuntu2.3

---------------
isc-dhcp (4.3.5-3ubuntu2.3) artful; urgency=medium

  * dhclient-script.linux: handle empty case also when waiting for ipv6 link
    local DAD. (LP: #1718568)

 -- Dan Streetman <email address hidden> Fri, 02 Mar 2018 13:14:51 -0500

[Łukasz Zemczak (sil2100)]

The verification of the Stable Release Update for isc-dhcp has completed successfully and the package has now been released to -updates. Subsequently, the Ubuntu Stable Release Updates Team is being unsubscribed and will not receive messages about this bug report. In the event that you encounter a regression using the package from -updates please report a new bug using ubuntu-bug and tag the bug report regression-update so we can easily find any regressions.

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.3.3-5ubuntu12.10

---------------
isc-dhcp (4.3.3-5ubuntu12.10) xenial; urgency=medium

  * dhclient-script.linux: handle empty case also when waiting for ipv6 link
    local DAD. (LP: #1718568)

 -- Dan Streetman <email address hidden> Fri, 02 Mar 2018 13:16:05 -0500

[Launchpad Janitor (janitor)]

This bug was fixed in the package isc-dhcp - 4.2.4-7ubuntu12.13

---------------
isc-dhcp (4.2.4-7ubuntu12.13) trusty; urgency=medium

  * dhclient-script.linux: handle empty case also when waiting for ipv6 link
    local DAD. (LP: #1718568)

 -- Dan Streetman <email address hidden> Fri, 02 Mar 2018 13:17:36 -0500