title: Detect another host with the same MAC address
body: <p>How can I detect if another host is using the same MAC address as the current host, e.g. because the other host is spoofing?</p>
  
  <p>I'm working in an embedded environment, so looking for answers on a protocol level, rather than “use such and such a tool”.</p>
  
  <p><strong>Edit</strong>: RARP does <em>not</em> solve this problem. For RARP to get any reply at all, there has to be at least one host on the segment which supports RARP. Since RARP is obsolete, modern operating systems don't support it. Furthermore, all RARP can do is tell you your own IP address - the response won't be any different if there’s another host on the segment with the same MAC, unless that host has itself used a different IP address.</p>