I was running nc in the background just to use the prompt again for nmap, which I was mistakenly executing in the server till now. And about nc, I don't have the netcat-traditional installed. It was always netcat-openbsd. Also, thanks for the explanation on nc and nmap.
Now, nc is run in the server in the foreground. nmap and telnet are run on my local machine now. The state of the port is now filtered (even after a server reboot) and telnet connection times out.
From what I have read from nmap manual,
I am sorry if something is evidently wrong with the rules above. I am yet to explore how networking works. Nor do I know much of the troubleshooting that I have to do now. I'll do some research online, but meanwhile if you have some troubleshooting that I can perform, or some resources to read, please do let me know.
Now, nc is run in the server in the foreground. nmap and telnet are run on my local machine now. The state of the port is now filtered (even after a server reboot) and telnet connection times out.
Code:
nmap xxx.xx.xx.xx -p 7890Starting Nmap 7.93 ( https://nmap.org ) at 2024-07-25 22:43 ISTNmap scan report for xxx.xx.xx.xxHost is up (0.13s latency).PORT STATE SERVICE7890/tcp filtered unknownNmap done: 1 IP address (1 host up) scanned in 1.50 secondsWhich probably explains why telnet times out too. My server runs Debian 12 that was upgraded from Debian 11 using full-upgrade. Debian 11 was installed using the cloud image downloaded from the Debian website. There are no front end firewalls installed. The only firewall like program is the iptable and the rule is as follows:Filtered means that a firewall, filter, or other network obstacle is blocking the port so that Nmap cannot tell whether it is open or closed.
Code:
sudo cat /etc/iptables/rules.v4# Generated by iptables-save v1.8.9 (nf_tables) on Thu Jul 25 12:57:12 2024*filter:INPUT ACCEPT [2712:274357]:FORWARD ACCEPT [0:0]:OUTPUT ACCEPT [1955:350557]-A INPUT -p tcp -m tcp --dport 7890 -j ACCEPTCOMMIT# Completed on Thu Jul 25 12:57:12 2024Statistics: Posted by debber — 2024-07-25 17:37