[systemd-devel] Prefix delegation and IPv6 subnetting

[Andrei Borzenkov]

On 07.07.2022 18:25, Bent Bagger wrote:
> 
> The prefix delegation problem starts with the interactions between net0 
> and net2. Net0 is delegated a /56 prefix from the main router (which 
> runs radvd and dhcpd6, not networkd, for historical reasons). I want 
> net2 to delegate a /60 subnet to net3, but it doesn't happen.


networkd does not support prefix subdelegation. It supports querying
upstream for delegated prefixes and allocating one /64 received prefix
to downstream interface announcing it via RA. The same functionality as
NetworkManager. Nor does networkd support DHCPv6 server functionality.

For all practical purposes IPv6 on-link prefix can only be /64. So
"delegated a /56 prefix" is misleading. You get delegated block of
prefixes that are aggregated into /56 mask.

I am not aware of any single program that would implement both client
and server side w.r.t. to prefix delegation. You can use one program to
query prefixes (client side) and use this information to update
configuration of another program (server side).