Explanation
To enable network printing, the firewall needs to open the ports that are used by the network printers and the print servers. Two common ports for network printing are 515 (LDP) and 631 (IPP). LDP stands for Line Printer Daemon Protocol, which is a TCP-based protocol for sending print jobs to a remote printer. IPP stands for Internet Printing Protocol, which is a HTTP-based protocol for managing and monitoring print jobs over the Internet. According to the CompTIA Core1 objectives, one of the network ports that is related to printing is
515. A research paper on network printing also mentions that LDP and IPP are widely used protocols for network printing.