Or IP all are eventually encapsulated in link-layer frames that are transmitted over physical media such as an Ethernet cable. Recall from the discussion from lecture 1 that messages exchanged by higher layer protocols such as HTTP, FTP, TCP, UDP, DNS, The packet capture library receives a copy of every link-layer frame that is sent from or received by your computer.
The packet sniffer, shown within the dashed rectangle in Figure 1 is an addition to the usual software in your computer, and consists of two parts. At the right of Figure 1 are the protocols (in this case, Internet protocols)Īnd applications (such as a web browser or ftp client) that normally run on your computer. Figure 1 shows the structure of a packet sniffer.
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