title: How do I get a MAC address for a remote system when I only know it's IP address?
body: <p>I'm working on a Wake on LAN service that will run from a web site and should interact with many different platforms - therefore, no Windows-only solutions.  When a user registers their system with the web site, I need to get the MAC address to use in constructing the <a href="http://en.wikipedia.org/wiki/Wake_on_lan#Magic_Packet" rel="nofollow noreferrer">"magic" packet</a>.  I have a Java Applet that is able to do this for me and am aware of an ActiveX control that will work, but I'm wondering if there is a way to do this server-side by querying routers/switches.  Since the system may be on any of a number of different physical subnets, using ARP won't work -- unless there's a way to configure the router(s) to perform the ARP on my behalf.</p>
  
  <p>Anyone know of any network APIs, proprietary or otherwise, that can be used to look up MAC addresses given an IP address?  I think we're using Cisco routers, but it's a complicated network and there may be multiple vendors involved at various levels.  I'd like to get some background information on possible solutions before I go to make a sacrifice to the network gods.  No point in abasing myself if it's not technically possible.  :-)</p>
  
  <p><strong>EDIT:</strong> We do have the network infrastructure set up to allow directed broadcast, though figuring out the exact broadcast address since netmasks are not always /24 is another conundrum that I need to solve.</p>