[systemd-devel] Prefix delegation and IPv6 subnetting

[Mantas Mikulėnas]

On Fri, Jul 8, 2022, 09:22 Andrei Borzenkov <arvidjaar at gmail.com> wrote:

> 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.
>

IME, "prefix" is a *very* common term for routed prefixes, not only on-link
ones – probably much more common than "/56 mask" (given that nothing uses
actual mask notation in IPv6). The upstream router doesn't care about
whether you're going to use it as on-link prefixes or not, anyway.
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