Is there an ethernet link layer protocol to get remote IPv4 settings?

Question

Given one or more embedded devices of the same type with some unknown IPv4 addresses or maybe no IPv4 addresses set at all: is there any Ethernet based network protocol to ”find“ those devices in the local net (LAN) from remote (PC) and get their IPv4 settings?

What not works for me:

• ARP: IP address must be known or only finds device I communicated with before (or ugly ARP floods …)
• LLDP: point to point only (?), so I would only see the switch between device and me. Also, just announces, no response on request (because there are no requests). Further: asking the switch (which supports LLDP) through SNMP is no option when using dumb switches
• IP based protocols: I played with UDP and broadcasts (both as request and response), but that does not work reliably if device and me are on different subnets, and it does not work at all if device has no IPv4 set.
• DHCP: does not work in networks without DHCP server, maybe no DHCP client on the embedded device

I assume others had the same problem before, take manufactures of network equipment like access points which should be configured remotely, powerline adapters, switches … all those where the vendor gives you some proprietary tool, the device shows up like magic in a list and you can assign some IPv4 then.

Of course the device must have some daemon listening and responding to certain requests, but what would be a standard protocol for such a task? Or do I have to make up some new protocol for that? May some of the above mentioned is possible, but I overlooked something?

Answer 1

Ethernet only provides a layer 2 connection, so anything Ethernet-based can't ever work across a router (ARP, LLDP - LLDP doesn't even cross a decent switch as it's link layer only).

Depending on the network, routed multicasts or directed broadcasts could work - normally they don't. All vendor tools I've seen just use (Ethernet) broadcasts and don't work across routers.

Most often, simple DNS is used for this purpose - the device registers with the DNS server or is preregistered and you just resolve the name.

Edit: without the router problem, the simplest way is to use a UDP broadcast to some unused port. With DHCP unavailable, the device could fall back to zeroconf (169.254.0.0/16) and broadcast from there.

Without IP, you'd need a "raw" Ethernet socket and use an Ethertype that doesn't interfere with normal network operations.