The VyOS config syntax currently does not support setting up a DHCPv6 server to hand out DNS settings such as nameservers and search domains to stateless clients.

Stateless clients are DHCPv6 clients that do not request an IP address. Typically they send a DHCPv6 "information request" message instead of the usual address assignment flow. This is typically used when addresses are assigned via SLAAC, but the client is sufficiently old that it does not support receiving DNS information via the RDNSS extension to the router advertisement. Sufficiently old clients include Windows 7 machines, and I've also observed this behavior in some fairly recent models of printers and Sony Blu-Ray players.

The isc-dhcp-server happily supports stateless clients, however it will only hand out parameters specified at the "shared network" level. The VyOS config syntax currently only support setting parameters at the subnet level. To enable support for this behavior, we should add the option to specify applicable parameters (such as name server and search domains) at the shared network level.