Duplex printing to an HP Laserjet P3005dn

[Eddie Lawrence]

I am attempting to do duplex printing to an HP Laserjet P3005dn. I am using the following command to send the print jobs:

lpr -#1 -P HP_LaserJet_P3005 -o sides=two-sided-long-edge -o media=Letter filename

The printer seems to ignore the "-o sides=two-sided-long-edge" option. The printer is capable of duplexing and does print both sides from Microsoft Office applications. I just can't get it to print duplex from Linux. Could this be a problem with the CUPS printer definition?