Enforcing duplexing in server hosted IPP queues

[Jose Hales-Garcia]

This is a beginner's question (again).

I have a CUPS server hosting IPP queues.  I want to enforce duplexing from the server.

I've tried setting the default option for the IPP queues to two-sided printing (along the long edge) using the CUPS web interface, but the jobs sent by the clients are printed out simplex.

I'm able to enforce server-side duplexing using LPD.  How can I do it with IPP?

The server is running on Mac OS X 10.6.6, if that makes a difference.

Sincerely,
Jose