Fallback to DHCPv6 if RA is never seen

[ColinMcInnes]

Sending out RSs, RA is never seen. Since we didn't see anything telling us to use DHCPv6 or SLAAC, dhcpcd doesn't ever send out a Solicit or Information Request

Is there currently a way to timeout on un-answered RS and fall back to DHCPv6 Solicit?

Keeping in mind the DHCPv6 address will be useless without a prefix in the DHCPv6 Advertisement.

[ColinMcInnes]

systemd/systemd#13770

Something like this, but I'm ok with waiting for a timeout, just in case the router is being dense.

[rsmarples]

I'm not sure what you're asking for here. As you say, any DHCPv6 reply would be pretty useless without a RA.
The systemd issue you link to is about requesting Prefix Delegation without a RA, which is possible with dhcpcd.

interface eth0
    ia_pd

You could also request ia_na or ia_ta and that will also start DHCPv6 without a RA. We just don't start DHCPv6 on any timeout - there's no point as any reply would be pretty useless I think.

[ColinMcInnes]

I'll give that a try. This is for cases where the router doesn't seem to send RA until after it has seen a DHCPv6 Solicit, or sends an RA without flags so we don't know which mode to use.

To clarify: the ISP start sending RA only once the first DHCPv6 exchange is done, and I'm not able to force networkd to start his DHCPv6 client... With my current isp, I receive RA packets but without the O or M flag. So even if DHCP is forced to "ipv6", the client is never started... systemd/systemd#16331