Saturday, August 20, 2022

Another Way To Check UDP Port to a Linux Server

In a previous post, I have shared a way to check for udp port allowance to a linux server using netcat and ngrep.

I have found out an even easier way to accomplish this, just by using netcat, without the need to install additional software like ngrep.

To do this, first we need to setup a netcat to listen to the udp port, in the target machine. For example, we wanted to test udp port 10000 allowance, just run below command on the target machine
$ nc -klu 10000
The command will hang there, waiting for a connection to be sent to it.

In the client machine, just use netcat to send some text over to the target machine, like below (assuming the ip address of the target machine is
$ echo "testing udp" | nc -u
If the udp port is not blocked, we will see the "testing udp" text printed on the terminal in the target machine, where we listen for 10000 udp, like example below

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