Hi, I am totally new to OpenWRT (don't kill me if I am doing something stupid).
I bought a Linksys router, have read OpenWRT documentation and setup my VLANs thanks to great tutorials on https://www.youtube.com/watch?v=qeuZqRqH-ug. My ISP modem is on bridge mode, everything seemed looking well (have connectivity and DNS working, zones blocking correctly, etc).
Now I tried to do some port scanning with NMAP to my public IP from a computer outside of my network. I did some simple TCP scan to all ports (-sT) and found some filtered ports and just port 21 OPEN. I see also run -sV to check this port 21 is tcpwrapped.
I tried then to identify what was listening to port 21 running
netstat -nutlp | grep 21 and there is nothing! Then I checked that I have no port forward rules, NAT rules or custom rules, and also no traffic rules mentioning port 21.
I would like to understand how this port is open... any hint?