Why can I not receive a response from a TCP/IP cap

问题:

My ultimate goal is to send a print job to a printer over the internet. The catch is that the printer is connected directly to a router, so I can't count on a computer processing anything.

The path a print job takes is: Computer -> Internet -> Router -> Printer

The printer is an Epson TM-T88V with the UB-E02 connect it module (it originally came with the 25-pin module).

The router is a D-Link DIR-655 with port 9500 redirected to LAN port 9100 and the LAN IP address of the printer. With this setup, I can enter the router's WAN IP address + port 9500 in a web browser and the printer spits out the HTTP request it receives.

From the terminal, if I use lpr (specifically lpr -h ip-address:9500 filename.txt), the printer prints the HTTP request it receives (not the file) and lpr appears to just be waiting for a response. According to the UB-E02 Technical Reference Guide, the Connect-It module supports lp/lpr.

Why is it that the printer prints the HTTP request and doesn't send a response back?

回答1:

The port you opened is likely the raw data dump port for the printer. Likely there is a seperate port which speaks RFC1179 that will speak to your lpr client.

You should not be sending HTTP control to either of these ports.