TCP/IP and Ports

~250 words · 2 min read

IP addresses

An IP address is a machine's address on a network — like a postal address for data. IPv4 (e.g. 192.168.1.10) is still the norm; IPv6 (e.g. 2001:db8::1) adds vastly more addresses.

TCP vs UDP

Two protocols sit on top of IP:

TCP — reliable, ordered, connection-based. Retransmits lost packets. Used for the web, email, SSH — anything where every byte must arrive.
UDP — fast, fire-and-forget, no guarantees. Used for DNS, video calls, games — where speed beats perfect delivery.

The three-way handshake

Before TCP sends data, the two sides establish a connection:

Client              Server
  |--- SYN -------->|   1. "Want to talk?"
  |<-- SYN-ACK ------|   2. "Yes, ready!"
  |--- ACK -------->|   3. "Got it, let's go"

Only after this exchange does real data flow. UDP skips all of it — it just sends.

The handshake is why a TCP connection has "latency" before the first byte. UDP starts instantly, which is why it powers real-time media.

Ports

A port identifies a specific service on a machine — an apartment number to the IP's street address. Well-known ports:

80 — HTTP
443 — HTTPS
22 — SSH
53 — DNS
3306 — MySQL

DNS