On the same local network, a phone can see a TV, a computer can see a printer, and a speaker can be used for casting, even when there is no dedicated DNS server doing local name resolution for them. When a device first joins the network, it may not even know who it is supposed to ask. Still, it has to recognize names first so that service discovery has somewhere to land.
Read MoreMany devices are not hard to see. The hard part is knowing what to do after you see them. On a local network, a printer may already resolve by name, but the client still does not know whether it actually offers printing, whether it uses TCP or UDP, what port to use, or whether it advertises extra parameters such as model, paper capabilities, or a path prefix. Knowing only that the machine is called printer.local is not enough to build the connection.