when you get a webpage, like Facebok, it comes into your computer in many small packets.

Let’s see what those look like!

Packets are split into a few sections (or “headers”)

ethernet/wifi

82:53:ac:99:2f:33 (MAC address)

“physical layer”: this gets changed constantly as your packet moves between computers

IP (“internet protocol”)

FROM: 172.96.2.3 TO: 123.9.2.32

in charge of getting your packet to the right server (like an address on an envelope)

TCP (or UDP)

sequence number: 877392 (counts bytes sent so far)
checksum: 8847 (detect corrupted data)
from: port 9979 to: port 80

in charge of preventing data corruption and helping you retry lost packets. video streaming uses UDP instead. UDP does not try to be reliable.

HTTP (or whatever)

GET / HTTP 1.1
Host: google.com
Accept-Language:en-US

the actual data you’re trying to send!