Suppose I connect two machines directly together with an ethernet cable. I know nothing about machine2's configuration - I only have access to machine1.
What can I do on machine1 to determine machine2's IP address? (Note that machine2 could have any possible IP.)
(The practical use for this is having a client connect a cellular router to their machine, and not having to do any configuration on their side for me to be able to then configure the cell router to talk to their machine.)