[SOLVED] Duplicate IPv6 addresses; /etc/machine-id not unique

[JChristensen]

I have three machines running LM19.1 Cinnamon 64-bit and they're being assigned duplicate IPv6 addresses. IPv4 addresses are unique and working fine.

If I understand correctly, DHCPv6 assigns addresses based on the DHCP Unique Identifier (DUID) as opposed to the MAC address, and the DUID in turn is based on the /etc/machine-id file.

Checking the machine-id files on my three machines, I found that they are identical. It seems like they should have been set up with unique values during installation. Other machines on the network running Ubuntu and Raspbian have unique values in /etc/machine-id and are not having issues with duplicate addresses.

Wondering if anyone can verify this issue, and how best to correct it.

[JChristensen]

I changed the machine-id file on one machine with

Code: Select all

# rm /etc/machine-id
# systemd-machine-id-setup
# reboot

This did indeed change the machine-id but the same IPv6 address was assigned. The default-duid value in /var/lib/NetworkManager/dhclient6[...].lease did not change so I must be barking up the wrong tree.

[JChristensen]

After generating the new machine-id file as above, I deleted the dhclient6-* files in /var/lib/NetworkManager and rebooted; now both the default-duid and the IPv6 address are different.

It seems like the Mint installation process should have set up unique machine-id files. Reading man machine-id it sounds like this could be a security issue. It was sure making SSH confusing.

Edit: Running the commands below on each machine seems to have fixed the issue. The machine-id files are now different as are the default-duid values. I can also see unique DUIDs via my router's administrative interface.

Code: Select all

$ sudo su
# rm /var/lib/NetworkManager/dhclient6-*
# rm /etc/machine-id
# systemd-machine-id-setup
# reboot