Need to change the port that GDC listens on

GDC port can be changed when required.

Why would you want to change the port that GDC listens on?

You may need to run several versions of the GDC on the same machine. Since each one must have its own listening port, Genero allows you to specify the port. If you run more than one and don't specify the port, Genero opens the next available port. For example, the first instance would open 6400, the next instance would open 6401.
>gdc <- The port assigned would be 6400 
>gdc -n <- The port assigned would be 6401 
>gdc -n -p 7400 <- The port assigned would be 7400 
>gdc -n -p 7400 <- The port assigned would be 7401 
>gdc -q -p 7400 <- GDC won't start since the port 7400 is already
assigned

Another reason to change ports might be that you can't use the ssh functionality. What if you haven't installed the SSH package yet, but you have more than one client behind the same firewall router? You can add rules to the router to send 6400 to the first client, 6410 to the second client, and so on. Each client would be started with the corresponding -p <port>, and the router would make sure each client gets the connections intended for it.