How do I become proficient in TCP Protocol

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Assuming you have done some sort of training and/or zelfstudy on TCP I suggest you look at the various video's from Laura Chappel wehere she digs into troubleshooting various issue.

There is a ton of sample capture files on Wireshark University that can be fun to look at and see if you understand the nature of the problem shown in the capture files.

Check out the movies like: https://www.youtube.com/watch?v=PLvrv... https://www.youtube.com/watch?v=jdIRf... https://www.youtube.com/watch?v=t5OJe... https://www.youtube.com/watch?v=LNeZZ...

There are loads of videos if you search for "wireshark tcp troubleshooting". TCP hasn't changed so a 10 year old video might even be better then a new one.

Enjoy them.