OK, so thanks to the help I've received here... I can remotely power ON/OFF my server.
This is currently working via IPMItool using UDP port 623. But I have multiple servers that I would like to be able to control. Currently, the port forwarding of the router is set to port forward UDP 623 to serverA. If I want to control serverB... I must edit the port forwarding in the router of UDP 623 to point it to serverB, etc.
This can be done remotely, but it is a hassle to have to do this each time I want to control a different machine. Ideally, I would want to setup multiple port forwards for all the servers and then use the IPMItool to specify which machine I wanted to control by changing the port used. But I can only make the IPMItool use port 623. (I thought I found that I could use the -p option to specify the port used by ipmitool, but it doesn't seem to work).
For example, if I port forward UDP port 40000 to a particular server and then tell the ipmitool to use -p 40000... it doesn't connect.