TCP/IP Basics

TCP/IP (Transmission Control Protocol / Internet Protocol) is the set of rules that allows devices to communicate over a network or the internet. It’s the foundation of nearly all modern networking.

What is IP?

IP (Internet Protocol) assigns a unique address to every device on a network, similar to a postal address. Data is broken into packets, each labeled with a source and destination IP address, and routed across the network to reach its destination.

Device A (192.168.1.10)  --->  Router  --->  Device B (192.168.1.20)
     |                                              |
  IP Address                                   IP Address
    

What is TCP?

TCP ensures that data packets arrive correctly and in order. Before sending data, two devices perform a “three-way handshake” (SYN, SYN-ACK, ACK) to establish a reliable connection. If a packet is lost, TCP requests it again.

IPv4 vs IPv6

• IPv4: format like 192.168.1.1 (32-bit, ~4.3 billion addresses)
• IPv6: format like 2001:0db8::1 (128-bit, designed to solve address shortage)

Private vs Public IP Addresses

• Private IP: used inside a local network (e.g., 192.168.x.x, 10.x.x.x) – not reachable from the internet directly
• Public IP: assigned by an ISP, reachable from the internet

Why IT Support Needs This

Understanding TCP/IP helps when troubleshooting “no internet access” issues – checking if a device has a valid IP address (via ipconfig on Windows or ifconfig/ip a on Linux/macOS) is often the first diagnostic step.

Common Interview Talking Point

“When a user reports they can’t access the network, I’d first check their IP configuration to confirm they have a valid IP address, then test connectivity to the gateway and beyond using ping and tracert/traceroute.”