Tcpdump

Debugging HTTP On Server With tcpdump

So you have a connectivity problem and for whatever reason (firewalls, urgency) you need to debug this on a remote server.

Enter tcpdump

This is a command line tool very much like Wireshark, with it you can see activity.

Here is a great blog post that gives a load of examples:

https://danielmiessler.com/study/tcpdump/

Debugging Connections with A Particular Host

If you need to figure out what is going on when the server tries to communicate with a particular host, try this:

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tcpdump -i any host 123.123.123.123 -vvv