TCP Test Tool for Mac OS X
Solution 1:
The closest free tool might be Nmap and the associated X11 GUI called Zenmap.
It's great, powerful, but the free means you will spend some time getting it set up and running since it's not like buying a desk but more like directions and only the hard to obtain parts needed to make yourself a desk.
You can download all the source for these and compile the programs. For someone familiar with command line and building open source unix tools it might be 30 to 90 minutes of effort to figure out any build errors and correct them.
I don't see an up-to-date package that lets you download and run Zenmap and it runs under X11 so if you are new to X11 - do read up a bit here or on the Apple discussion boards - it's just a little different than a normal mac program so you might also spend some time learning X11 before you will be running the tool.
I don't mean to make any of this seem overly hard. A motivated but absolute beginner can get this all done in a day with luck - just that it's not something you will have running in 5 minutes. Your curiosity to debug networking might make this a great journey in learning how the software really works by looking at the code and seeing the tool actually run.
Solution 2:
You might also find Wireshark useful. I found a good video on Youtube to getting it setup.
http://www.youtube.com/watch?v=IxeHm0BKdwc
All the steps in the video may no longer be necessary as the changelog for version 1.6.0 says the following:
Wireshark is now distributed as an installation package rather than a drag-installer on OS X. The installer adds a startup item that should make it easier to capture packets.
Solution 3:
I can definitely recommend Packet Sender for sending and receiving TCP and UDP packets.
Here are some of the advantages:
- More focused than WireShark (which core functionality is capturing and analyzing existing traffic) and Nmap (which is mainly a security tool)
- Super-simple utility with GUI, no learning curve
- Open-source and free
- Cross-platform