The Internet: Packets, Routing & Addresses

You’ll be able to

Describe how data is divided into packets and reassembled
Explain how routing moves packets across many possible paths
Explain the role of IP addresses and the Domain Name System

A network of networks

The Internet is a global system of interconnected computer networks — literally a network of networks. No single computer or company controls it; instead, independently owned networks agree to connect and pass along each other’s traffic. Devices connect through routers, and data hops from router to router across many networks to travel from source to destination. This decentralized design is deliberate: it lets the Internet grow without central coordination and keeps working even when individual parts fail.

Packets and reassembly

Data does not travel the Internet in one piece. A message is broken into small chunks called packets, each carrying a portion of the data plus metadata — including the destination address and the packet’s position in the sequence. Packets are sent independently and may take different paths and arrive out of order. The receiving computer uses the sequence information to reassemble them into the original message and can request any missing packet again. Splitting data into packets lets the network share links efficiently and route around trouble.

Addresses and names

Every device on the Internet has an IP address, a numeric label that identifies it so packets can be routed to it — like a mailing address for a computer. Because numbers are hard to remember, the Domain Name System (DNS) translates human-readable names like example.com into the IP address of the server that hosts it. Routing is the process by which routers choose a path for each packet toward its destination IP address; with many possible paths, the network can steer around congested or broken links.

Path of a web request

name (example.com) → DNS lookup → IP address → packets routed hop-by-hop → reassembled at destination

DNS turns a name into an IP address; the message is split into packets that are routed independently and reassembled at the other end.

Worked example

You load a large web page and the packets arrive out of order, with one packet lost along the way. How does your computer still reconstruct the page correctly?

1.Each packet carries metadata including its position in the sequence, so order of arrival does not matter.
2.Your computer buffers the packets and uses the sequence numbers to place them back in the original order.
3.It detects that one sequence number is missing, so the page is incomplete.
4.It requests the missing packet be resent; once it arrives, the full ordered message is reassembled.

Answer: Because every packet is labeled with its position, the receiver reorders arriving packets and detects the gap left by the lost one, then requests a resend. Sequence metadata plus retransmission make reliable delivery possible even over an unreliable, out-of-order network.

Checkpoint

When a large file is sent across the Internet, why is it broken into packets that may travel different routes?

Tip

Think of packets as pages of a letter mailed in separate envelopes, each numbered. They may arrive out of order or one may get lost, but the numbering lets the receiver reorder them and ask for any missing page again.

Checkpoint

What is the primary role of the Domain Name System (DNS)?

On the exam

Keep the roles distinct: IP addresses identify devices, DNS turns names into IP addresses, and routing picks each packet’s path. The exam mixes these up in answer choices on purpose.

Answer the 2 checkpoints as you read.