IPv6 DUID determination

[Beniamino Galvani]

On Sun, Jul 07, 2024 at 11:51:17AM +0000, Jaap Winius wrote:
> 
> Hi folks,
> 
> Can someone here can please tell me what the easiest way is to determine or
> predict the unique IPv6 DUIDs of systems that use NetworkManager 1.30.6 or
> higher?

The easiest way is to set 'ipv6.dhcp-duid=ll' in the connection; then
the DHCPv6 DUID is composed in the following way:

 https://datatracker.ietf.org/doc/html/rfc8415#section-11.4

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         DUID-Type (3)         |    hardware type (16 bits)    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      .                                                               .
      .             link-layer address (variable length)              .
      .                                                               .
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                         Figure 7: DUID-LL Format

The hardware type for Ethernet is 1.

If you want to set DUID-LL to be default for all connections on a
machine, add a file /etc/NetworkManager/conf.d/50-dhcpv6-duid-ll.conf
containing:

[connection-duid-ll]
ipv6.dhcp-duid=ll

Otherwise if you have a system that is already using a different DUID
generation mode, for example DUID-UUID, you can discover the value by
inspecting file /run/NetworkManager/device/$ifindex, which contains
among other things:

[dhcp6]
dhcp6.dhcp6_client_id=00:03:00:01:86:f1:6b:0d:5e:9e

This information is available only since NM 1.42.

Beniamino

> This is with the integrated DHCP clients. Knowing each DUID is
> necessary to configure my DHCPv6 server to always give these hosts the same
> IPv6 addresses.
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