Sounds OK, superficially – I know almost nothing about dhcpcd or the protocol.

@vcunat To elaborate more: The data is sent during DHCPv6 solicitation. The packet looks like this (look at the last two):

It surely works here with my router, but I don't know if other routers could fail. I doubt it but you never be sure…

I don't think we should make this change because some routers may reject this vendorclassid, and the user cannot override it in extraConfig. As per dhcpcd.conf(5):

vendclass en data
Add the DHCPv6 Vendor Indetifying Vendor Class with the IANA assigned Enterprise Number en with the data. This option can be set more than once to add more data, but the
behaviour, as per RFC(3925) is undefined if the Enterprise Number differs.

So I'm afraid it's up to the user to set this manually if they want to expose less information.

@xeji So do you think it would be okay if I do it as optionalString?

I could see this being an optional value but it being open to the user to customize. In a datacenter, pxebooting machines could declare some other options to the dhcp server for it to take some other action. But I agree with @xeji that the default shouldn't change.

@cransom That's not a new feature compared to the currently existing extraConfig functionality. I'll close this PR, users can add the appropriate line to their configuration if they wish.

Explicit nixos options are easier to compose etc. but I suppose it's not a big deal in this case.

Totally agree. We should rather keep the options clean