In my house I have an Asus AX88U router, distributing addresses in the 192.168.0.x range and another GL-300M16 router distributing addresses in the 10.0.20.x range.
These two routers are interconnected via Wifi, with static routing between them.
I can ping between computers on both subnets.
The problem is that on the GL-300M16 network, there is a label printer (Zebra) that uses port 9100. I can communicate and print labels through a computer on the same subnet (10.0.20.x), but I cannot print from a computer located on the other subnet (192.168.0.x).
Remembering that I can ping the printer normally.
Do I need to open or forward port 9100?
If positive, how do I do it? I tried, but I don’t know if I was doing it correctly.
Without knowing the specific firmware version of the Shadow (GL GUI → System → Upgrade) it’s hard to tell… but here’s how to confirm the port is open. You’ll need to SSH into the Shadow. See below for specifics on all that.
root@flint:~# opkg update; opkg install nmap
root@flint:~# nmap -p 9100 $printerIPGoesHere
Thanks for answering.
The router is using the latest firmware (4.3.7).
I’m sorry, but I don’t have much experience with Nmap and I’m not sure I understand it correctly.
I think you want me to check if I can access port 9100 through the GL-AR300M16.
What happens is that the printer (10.0.20.101) is part of the LAN of this router (10.0.20.x), so I have no difficulty printing within this subnet. The problem occurs when I try to print from a computer on the Asus router’s subnet (192.168.0.x).
I can do a ping test between these networks and everything is OK. The problem seems to be exactly happening with port 9100.
I did some tests yesterday using it, including putting both the computer in DMZ mode on the Asus, and I also put the printer in DMZ mode on the GL-AR300M16. The problem persisted. No printing.
Ah, 4.3.7; good to know. The GL docs still link to v3. For v4.x, you should find it under GL GUI → Network → Firewall → Open Ports on Router → [ Add ] .
nmap is a command line tool to scan for open ports on a remote host/device; in this case I was going to get you to scan whatever subnets you had to confirm the port to the printer’s IP was indeed open. Such tools is also available for phones/mobile devices, if that helps… & features a GUI.
This is assuming you, of course, have a Android device & F-Droid already installed for the very best in Free & Open Source Software 
(I don’t use Apple & try to stay away from closed sourced software when possible). I’m pretty sure there’d be something similar for iOS, though.
If opening the port doesn’t work, I question if Port Forwarding isn’t the method to use here.
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