This problem has been happening to me recently with up to date Ubuntu 16.04 amd64 desktop.
Workaround is to clean up the broken state by removing all leases:
1. Disconnect from the network in Network Manager
2. Execute: sudo rm /var/lib/NetworkManager/dhclient*.lease
3. Connect to the network in Network Manager
After this dhclient -6 keeps running and IPv6 leases are renewed correctly.
I had this problem on a second very similar installation. There it has been verified that dhclient -6 process is killed/crashed right after acquiring the IPv6 address, so I had a second reproduction.
I saved the contents of /var/lib/NetworkManager and can send it to the developer fixing it on request. There must be something there crashing dhclient in IPv6 mode.
This problem has been happening to me recently with up to date Ubuntu 16.04 amd64 desktop.
Workaround is to clean up the broken state by removing all leases:
1. Disconnect from the network in Network Manager NetworkManager/ dhclient* .lease
2. Execute: sudo rm /var/lib/
3. Connect to the network in Network Manager
After this dhclient -6 keeps running and IPv6 leases are renewed correctly.
I had this problem on a second very similar installation. There it has been verified that dhclient -6 process is killed/crashed right after acquiring the IPv6 address, so I had a second reproduction.
I saved the contents of /var/lib/ NetworkManager and can send it to the developer fixing it on request. There must be something there crashing dhclient in IPv6 mode.