What ports to open on a firewall for printing to a HP LaserJet CP1525nw

Question

I'm trying to open ports on a firewall for a sub-network to be able to print to a wireless printer (HP LaserJet CP1525nw) from the main network (which is behind a firewall also). What ports would I need to open to be able to do printing and to access the management web interface on the printer?

Solution

You need a number of ports:
For the actual printing port 9100 (tcp). This is the HP JetDirect print protocol, which, as far as I know, all HP Laserprinters use.
For the web-interface the normal HTTP port 80 (tcp).
For printer-status (which is what Windows REALLY likes, else it keeps telling you the printer is off-line) you also need to open the SNMP protocol. That is port 161 and this can be either UDP or TCP so you best open it for both (or just for IP in general, which covers both).
Additonally it can't hurt to open port 631 (IPP protocol) which is used by CUPS (Linux and MacOS) as prefered printer-protocol. Cups can fall-back to JetDirect if neccessary, but if IPP is available gettting the printer setup on Linux or MacOS is a bit easier.