Internet Layer (TCP IP) - buaamer81/IT130-Networking-Wiki GitHub Wiki

Internet Layer (TCP/IP Model)

📘 Overview

The Internet Layer is the third layer in the TCP/IP Model.
Its primary job is to handle logical addressing and routing so that data can travel across multiple networks (even across the world).

Think of it as:
“How does your data know where to go — from your home network to Google’s servers?”

🔧 Key Responsibilities

Logical addressing using IP Address (IPv4/IPv6)
Routing packets across different networks
Packet creation & delivery
Path determination (choosing the best route)
Error handling (ICMP reporting)
Address resolution (mapping IP to MAC)

📦 Data Unit: Packet

At the Internet Layer:

Data from the Transport Layer is encapsulated into Packets
Each Packet contains:
- Source IP Address
- Destination IP Address
- Data payload

🔁 Protocols at the Internet Layer

Protocol	Purpose
IP (Internet Protocol)	Logical addressing and packet delivery
ICMP (Internet Control Message Protocol)	Error reporting and network diagnostics
ARP (Address Resolution Protocol)	Resolves IP to MAC addresses
IGMP (Internet Group Management Protocol)	Multicast management

🛠 Devices Operating at the Internet Layer

Device	Function
Router	Reads IP addresses, forwards packets to next network
Layer 3 Switch	Combines switching & routing at high speed

🧠 Real-Life Scenario

Sending an email to someone across the globe:

The Internet Layer assigns source & destination IP addresses.
Packets are routed through multiple routers.
Each router reads the destination IP and forwards the packet closer to the recipient.

🧪 Troubleshooting at Internet Layer

Issue	Cause
Unreachable host	Incorrect IP, Routing problem
Wrong path	Routing misconfiguration
Packet loss	Congestion or faulty routes
No IP Resolution	ARP or DNS issues

Tools to troubleshoot:

ping
tracert / traceroute
ipconfig / ifconfig
arp -a

📊 Visual Aids

🔁 Related Pages

Return to: TCP/IP Model Overview