Hi

This is on Ubuntu 14.04

I assign ipv6 address statically using ip -6 addr add
When I bring the interface down using ip link set
or ifconfig, the ipv6 address gets deleted. After setting
the interface back up, the ipv6 address is not restored.
Who is deleting the ipv6 address and why and How can I stop it?

I've tried this after stopping network-manager also, but the same behavior
persists

root@nasir-VirtualBox:~# stop network-manager
network-manager stop/waiting
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~# ip addr show eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:8e:9b:ec brd ff:ff:ff:ff:ff:ff
inet6 fe80::a00:27ff:fe8e:9bec/64 scope link
valid_lft forever preferred_lft forever
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~# ip -6 addr add 4455::1/64 dev eth1
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~# ip addr show eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:8e:9b:ec brd ff:ff:ff:ff:ff:ff
inet6 4455::1/64 scope global
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe8e:9bec/64 scope link
valid_lft forever preferred_lft forever
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~# ip link set eth1 down
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~# ip addr show eth1
3: eth1: <BROADCAST,MULTICAST> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
link/ether 08:00:27:8e:9b:ec brd ff:ff:ff:ff:ff:ff
root@nasir-VirtualBox:~#
root@nasir-VirtualBox:~# start network-manager
network-manager start/running, process 8463
root@nasir-VirtualBox:~# ip addr show eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:8e:9b:ec brd ff:ff:ff:ff:ff:ff
inet 10.0.3.15/24 brd 10.0.3.255 scope global eth1
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe8e:9bec/64 scope link
valid_lft forever preferred_lft forever
root@nasir-VirtualBox:~# uname -a
Linux nasir-VirtualBox 3.16.0-41-generic #55~14.04.1-Ubuntu SMP Sun Jun 14 18:43:36 UTC 2015 x86_64 x86_64 x86_64 GNU/Linux
root@nasir-VirtualBox:~#

root@nasir-VirtualBox:/home/nasir/tools# ip addr show eth1
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
link/ether 08:00:27:8e:9b:ec brd ff:ff:ff:ff:ff:ff
inet 10.0.3.15/24 brd 10.0.3.255 scope global eth1
valid_lft forever preferred_lft forever
inet6 fe80::a00:27ff:fe8e:9bec/64 scope link
valid_lft forever preferred_lft forever
root@nasir-VirtualBox:/home/nasir/tools#

If you want your IPv6 address to remain then you need to edit the config file for the interface and add it. It is being deleted because every time you start the network the config file is read and applied. If the IPv6 address isn't there it doesn't get applied.

Thanks Robert for the reply. Is there anyway the config file mechanism can be disabled. I want my software to provision and deprovision the IPv6 addresses based on
user CLI

It's going to have to be configured somewhere. So if you are manually setting it then you have to manully set it everytime you restart the interface.