TCP/IP is the backbone of modern networking. Understanding how it works is essential for anyone managing servers or networks.

The Four Layers

TCP/IP has four abstraction layers:

1. Application — HTTP, SSH, DNS, SMTP
2. Transport — TCP, UDP
3. Internet — IP, ICMP
4. Link — Ethernet, WiFi

IP Addressing

IPv4 addresses are 32-bit numbers written as four octets:

192.168.1.1

Key concepts include subnet masks (255.255.255.0), CIDR notation (192.168.1.0/24), and the distinction between public and private addresses.

TCP Three-Way Handshake

Every TCP connection starts with a three-way handshake:

1. SYN — Client sends a synchronize packet
2. SYN-ACK — Server acknowledges
3. ACK — Client confirms

This ensures both sides are ready to communicate reliably.

Common Ports

Service	Port
HTTP	80
HTTPS	443
SSH	22
DNS	53

Knowing TCP/IP fundamentals helps you troubleshoot connectivity issues and configure firewalls effectively.