To change the interface back to using DHCP and so have it allocated a different IP address
netsh interface ip set address "Local Area Connection" dhcp
netsh interface ip set dns "Local Area Connection" dhcp

Once I'd figured out the commands to use and put them together into two batch files (static.bat and dhcp.bat) I had a method that was sufficiently quick and easy to reproduce the bug I'd started out investigating.

However, this method has a significant drawback. Every time we toggle from static to DHCP or vice versa, the network interface goes down and back up again. This means we lose all connections to network drives, any existing telnet sessions, VNC sessions etc. Fortunately the client and the server I was debugging used a connectionless protocol (not TCP) and so the interface coming down did not prevent them from communicating further. However, with only one desktop machine at my disposal, debugging the server process running on a remote Linux box was proving to be difficult when the ssh session fell down each time.

With a bit of time and a lot of help from free and open source software, this problem can be overcome and we can change the effective IP address of our client program as seen from the server without tearing down all the ancillary connections needed to investigate what's going on. I'll explain how in the next installment.