Reminder: how to listen with netcat


A little reminder on how to put netcat in listen mode.

It occurred to me that I needed to setup a little listener on a machine to see if traffic was going through correctly. What better tool than netcat to do this?!?

It turns out that I didn’t remember almost at all how to use it. I first tried this:

netcat -l 54321

Nice try, Flavio! But to listen to port 54321 you need to use option -p, so…

netcat -l -p 54321

… is closer but still not correct, because to set the listening address you need to use option -s, which leads us to…

netcat -l -p 54321 -s

… which, in the end, is correct.

Then, of course, take a deep look at your iptables -vnL, because traffic might get trapped there!

Oh My!

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