Is there a way, via standard ethernet layer2 protocols, to test latency to a device without using it's IP address?
I have a fibre "box" provided by my ISP physically connected to my router via copper ethernet. The ISP gave me the IP address of the device after I asked for it in order to run latency graphing using smokeping.
Unfortunately it seems the device's IP address is not locally routable, meaning traffic to the device goes out to the ISP's core network, probably to another city, and only after that does it come back down the fibre service to the device. Instead of less than 1ms, latency to the on-site device is about 20ms. By comparison, latency to the ISP's core router in my city is about 800μs.
I do not have configuration access to the device, therefore I cannot set up a "local" IP. The ISP also refuses to add such an IP to the device - likely because it would then not conform to how all their other on-site devices are configured.