How does Wireshark know which protocol a packet uses, especially higher-level protocols like HTTP and TCP, which don’t operate at the network layer?

What I understood from my computer networks class is that packets are exchanged at the network layer and encapsulate all the segments received from the transport layer in the packet’s payload. A single transport layer segment might be broken down and sent across as multiple packets. So how does Wireshark know if a packet is TCP or UDP? Does it look inside the payload to determine it?

Some packets are shown to be using an application layer protocol like HTTP while others use transport layer protocols like TCP/UDP. In the case of the packets using TCP/UDP, which application layer protocol do these packets belong to?

submitted by /u/pseudopodia_
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March 1, 2023
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