Once the file has been transferred, the connection will close automatically. Using a second laptop (macbook pro), connect to the listening nc process, feeding it the file which is to be transferred: I am going start nc to listen on a specific port such as 4242, with output captured into a file called file.output: Now use IPv6 addresses only for $ nc -w 2 -v -6 443 More examplesĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != ĭNS fwd/rev mismatch: != For example, run the dig command/ host command as follows: The last command used IPv4, and it is useful when remote hosts have IPv4 and IPv6 addresses. Let us scan for UDP port 1194 (OpenVPN) or WireGuard VPN UDP port 31194: -6 : Make sure we use IPv6 version addresses only.-n : Use numeric-only IP addresses i.e.I will leave that for another blog post.Īnd if you want to validate that netcat is indeed listening on that port, you can connect to that port from another workstation by using nmap.Fig.01: Linux/Unix: Use Netcat to Establish and Test TCP and UDP Connections on a Server Have to dig deeper and see what it really means though. The -L means “listen harder, re-listen on socket close” :). If you run this on a Windows 7 machine, you will get this dreaded message “local listen fuxored: INVAL”. The command to have netcat listen on a specific port is “nc -l PORT_NUMBER”. You can download the windows port of the tool at If I am not mistaken, nc comes as a default tool in most of the Linux distros. You can run netcat on your workstation to listen on port 80, assign the IP address of the web server to your workstation and test the rule. But your web server is not built yet and you want to validate the rule. For example, say, you configured your firewall to allow TCP 80 traffic to your web server. You can use it to listen on certain ports or connect to certain ports. Netcat is a swiss army tool for network/security professionals.
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March 2023
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