Studying packet captures is one of the best methods to learn the operation of protocols in any of the 7 network layers. It doesn’t matter if they were made in wireshark, tshark, tcpdump or any other program.
Thanks to the work of very good people we do not need to create the conditions ourselves and make these captures. There are several “capture banks” available for us to enjoy and learn from:
Packetlife.net
Number one! well known by many, the bank of Jeremy Stretch.
https://packetlife.net/captures/
Chris Sanders github
Chris Sanders is the author of several books focusing on information security and packet capture analysis. The captures are not available directly on his website but in a github repository.
https://github.com/chrissanders/packets
njrusmc.net
While preparing to write this post I found one more page with wireshark packet captures. The “Job Aids” page from Nick Russo, also an author of several publications and training for CCIE and CCDE certifications.