Comment 21 for bug 1718568

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 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: 10105, p: 0).
XMT: Forming Request, 0 ms elapsed.
XMT: X-- IA_NA 00:bf:16:8a
XMT: | X-- Requested renew +3600
XMT: | X-- Requested rebind +5400
XMT: | | X-- IAADDR 2001:db8::99
XMT: | | | X-- Preferred lifetime +7200
XMT: | | | X-- Max lifetime +7500
XMT: V IA_NA appended.
XMT: Request on ens7, interval 940ms.
RCV: Reply message on ens7 from fe80::5054:ff:fec9:897c.
RCV: X-- IA_NA 00:bf:16:8a
RCV: | X-- starts 1520535277
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
PRC: Bound to lease 00:01:00:01:22:2c:61:12:52:54:00:c9:89:7c.

-proposed package verified