[systemd-devel] networkd: IPv6 prefix delegation not updated when prefix changes

[Tobias Brink]

Andrei Borzenkov <arvidjaar at gmail.com> writes:

> 13.04.2020 18:18, Tobias Brink пишет:
>
> DHCPv6 IA prefix option includes lifetime. Client is expected to renew
> delegation before lifetime expires. If information handed out to client
> expires before this timer, standard defines Reconfigure message that can
> be used by server to inform client that it needs to renew lease. In both
> cases it is really up to provider and its equipment.

I did check this. Unfortunately, the CPE does not send a Reconfigure
message. That would be the best, but there's nothing I can do about
it.

Nevertheless, that's not the whole issue. As stated in the other
subthread, when the prefix is up for renewal, networkd sends a request
and gets a NoBinding reponse because the prefix is no longer valid. At
that point, it keeps retrying the (now) invalid prefix instead of
requesting a new one. The (now) invalid routes are also never removed.

I will re-test this extensively with the git master version of networkd
and open an issue just on that part if it still occurs there.

> Still even if all of this is implemented there is still some short
> period of lost connectivity, before client has renewed delegation and
> pushed updated information downstream. To make it completely transparent
> provider would need to keep both prefixes as valid for some transitional
> time.

I am in fact not 100% sure if the old routes do not stay valid for a
(very?) short time, I would have to do some testing. I suspect that the
lifetimes passed on by the CPE do not necessarily reflect the ones on
the ISP side. Not the most important for me, though, because I can set
the renewal time to be in the night in the CPE so that I mostly wouldn't
notice. The primary concern for the moment is to get the new prefix at all.

Tobias