Here’s how to find out the IP address of the DHCP Server your Mac is currently using to obtain it’s IP address.
ipconfig getoption en0 server_identifier
You can also do more with ipconfig, things like determine the router address for an interface:
ipconfig getoption en0 router
this is sure easier than what I used to do:
netstat -nr | grep default | awk ‘{print $2}’;
this method, however, returns the system-wide default router whereas the ipconfig method returns the router for an individual interface. replace en0 for en1 if using AirPort…