A packet crosses the internet one hop at a time. Each machine looks at the destination address on the packet. It passes the packet along to the next connected machine. Choosing which way to send a packet toward its destination is called routing, and routers are the machines that do it.
IP addresses of the older kind, IPv4, are 32 bits long, which means four 8-bit parts. As of November 2026, IPv6 is a newer version of the Internet Protocol that allows many more different addresses than IPv4.
IP is a "best efforts" service. It tries to deliver packets, but it cannot promise that they all arrive or that they arrive in order. Every IPv6 packet carries a hop limit. Each router lowers this number by one as it passes the packet on, and if the number reaches zero, the packet is thrown away. This keeps stray packets from circling the network forever.
TCP sits on top of IP. It notices lost packets by their sequence numbers, then sends them again. Before two computers swap data over TCP, they set up a connection with a three-way handshake. The first computer sends a SYN message, the second answers with SYN-ACK, and the first replies with ACK. Then the connection is open and the computers can pass data back and forth.
In 1983, DNS was developed because keeping a list of every computer's number and name could not keep up with the internet's growth. A resolver is a program that asks name servers for the answer to a client's question about a domain name. If a DNS server does not know a website's address, it can ask another DNS server, and root servers know where to look.
Internet exchange points are places where internet service providers swap data directly with each other. An exchange point is run on switches that connect the networks taking part. A content delivery network, or CDN, is a group of servers spread out over many places. The servers keep copies of data. They answer each request from the server closest to the person asking.
A company called a registrar sells a domain name for a website, and a registry runs each top-level domain such as com. The Internet Assigned Numbers Authority keeps public lists, called registries, of identifiers such as domain names and IP addresses so they are assigned without clashing.
Cables under the sea are laid from cable ships that carry thousands of miles of coiled cable. Near shore, where fishing and anchors are a danger, the ship tows a plough that cuts a furrow for the cable. In the deep sea the cable is simply laid directly on the ocean floor.
Between 2007 and 2014, fish bites, a category that includes sharks, caused zero cable faults. As of November 2026, most damage to these cables comes from human activity such as fishing and ships dragging anchors, not from sharks, and repairs can take weeks or months because of permit rules, customs delays and other hurdles.
Companies spread their traffic across several cables, so if one breaks the network keeps running over the others while the broken one is repaired. As of November 2026, almost all the data that travels between countries goes through cables laid on the sea floor.
Words to know
- routing: choosing a way
- handshake: connection setup
- resolver: DNS asker
- registrar: domain seller
- registry: runs a domain
