Tag Archives: Telnet

Basic TCP and UDP Demos w/ netcat and telnet

I am currently working on a network & security training, module “OSI Layer 4 – Transport”. Therefore I made a very basic demo of a TCP and UDP connection in order to see the common “SYN, SYN-ACK, ACK” for TCP while none of them for UDP, “Follow TCP/UDP Stream” in Wireshark, and so on. I wanted to show that it’s not that complicated at all. Every common application/service simply uses these data streams to transfer data aka bytes between a client and a server.

That is: Here are the Linux commands for basic lab, a downloadable pcap, and, as always, some Wireshark screenshots:

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PAN Blocking Details

One of my readers sent me this question:

We have an internal discussion about whether it is possible to block the 3 way hanshake TCP but allow the JDBC application protocol. In other words we would like to block the test of the port with the command “telent address port” but we would like that the connections via JDBC continue to work. is it possible to do this theoretically? Is it possibile to do it with paloalto firewall?

Let’s have a look:

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