If you’re just starting out in networking you’ll likely read a lot of documents, books, blogs and such, that explain how packets work. You’ll see fancy diagrams that show how ARP works, DNS, DHCP, and a whole slew of other protocols that make the network work as it should. These are good learning aids, but what you might want to focus on is the data itself. You can analyze data using the free application, Wireshark.
When you enable a capture with wireshark on a live network you’re probably going to see more than you want. This will make it hard to learn. I recommend installing Wireshark and then downloading some of the sample captures. These will give you something specific to look at and ease you into a live capture.
Another method good for learning is using the wireshark capability built into GNS3. Simply right click on a link between two devices and select the “Start capturing” option.
Learning how to use wireshark will benefit you in your networking career and help you to gain a much better understanding of network traffic.