Gimp::Net is a communication module for the gimp-perl server.
For Gimp::Net (and thus commandline and remote scripts) to work, you first have to install the "Perl-Server" extension somewhere where Gimp can find it (e.g in your .gimp/plug-ins/ directory). Usually this is done automatically while installing the Gimp extension. If you have a menu entry < Xtns/Perl-Server > then it is probably installed.
The Perl-Server can either be started from the < Xtns > menu in Gimp, or automatically when a perl script can't find a running Perl-Server.
When started from within The Gimp, the Perl-Server will create a unix domain socket to which local clients can connect. If an authorization password is given to the Perl-Server (by defining the environment variable GIMP_HOST before starting The Gimp), it will also listen on a tcp port (default 10009).
Since the password is transmitted in cleartext, using the Perl-Server over tcp effectively lowers the security of your network to the level of telnet. Even worse: the current Gimp::Net-protocol can be used for denial of service attacks, i.e. crashing the Perl-Server. There also *might* be buffer-overflows (although I do care a lot for these).