Logical Addressing

🤔 What is Logical Addressing? (Basic Idea)

In a network, devices must have addresses so that data knows:

• 📤 Where it comes from

• 📥 Where it has to go

📌 At the Network Layer, this addressing is called Logical Addressing.

👉 Logical addressing is mainly done using IP addresses.

🧠 Simple Definition

📌 Logical addressing is the method of assigning logical (software-based) addresses to devices so they can be identified and located across different networks.

🧠 Why Is It Called “Logical”?

Because:

• It is not hardcoded into hardware

• It is assigned by software or network administrator

• It can be changed easily

📌 This is different from MAC address, which is physical and fixed.

🆚 Logical Address vs Physical Address

🌍 Why Logical Addressing Is Needed

Imagine this scenario 🚚:

• A courier needs to deliver a package

• Just knowing the house color is not enough

• It needs:

  • City

  • Area

  • Street

  • House number

📌 Logical addressing works the same way:

• Helps locate devices globally

• Works across multiple networks

• Enables routing

🧠 Role of Logical Addressing in Network Layer

Logical addressing helps the Network Layer to:

• 🌐 Identify source and destination devices

• 🛣️ Route packets across networks

• 🔁 Support internetworking

• 📦 Deliver packets correctly

🌐 IP Address – The Logical Address

🔹 What is an IP Address?

An IP (Internet Protocol) Address is a unique logical address assigned to each device in a network.

📌 It identifies:

• Network

• Host within that network

🧠 Simple Definition

📌 An IP address is a numerical label assigned to a device to identify it uniquely on a network.

🔢 Versions of IP Addressing

There are two versions:

1️⃣ IPv4

2️⃣ IPv6

📌 In this topic, we focus mainly on IPv4 basics.

📘 IPv4 Addressing (Introduction)

🔹 Structure of IPv4 Address

• Length: 32 bits

• Divided into 4 bytes (octets)

• Each byte = 8 bits

📌 Written in dotted decimal format

👉 Example:

192.168.1.1

🧠 How IPv4 Address Is Divided

An IPv4 address has two main parts:

1️⃣ Network ID

2️⃣ Host ID

📌 This division helps routers understand:

• Which network the device belongs to

• Which device inside that network

🧩 Example

IP Address: 192.168.1.10

• Network part → 192.168.1

• Host part → 10

🏷️ Network ID vs Host ID

📌 All devices in the same network share the same Network ID.

🧠 Logical Addressing & Routing

Routers use logical addresses (IP) to:

• Decide best path

• Forward packets

• Connect different networks

📌 Without logical addressing:

• Routing is impossible ❌

• Internet cannot work ❌

🧠 Static vs Dynamic Logical Addressing

🔹 Static IP Address

• Assigned manually

• Does not change

📌 Used in:

• Servers

• Routers

• Printers

🔹 Dynamic IP Address

• Assigned automatically (using DHCP)

• Changes over time

📌 Used in:

• Home users

• Mobile devices

🧠 Private vs Public IP Address (Basic Idea)

🔒 Private IP Address

• Used inside local networks

• Not accessible from Internet

Examples:

• 192.168.x.x

• 10.x.x.x

🌍 Public IP Address

• Used on the Internet

• Globally unique

📌 Assigned by ISP.

🧠 Logical Addressing vs Naming

📌 DNS converts names into logical addresses.

✍️ Exam-Oriented Definitions

📌 Logical Addressing:

Logical addressing is the Network Layer mechanism of assigning IP addresses to uniquely identify devices across networks.

📌 IP Address:

An IP address is a logical numerical identifier assigned to a device in a network for communication.

⭐ Advantages of Logical Addressing

• Supports large networks 🌍

• Enables routing

• Flexible & changeable

• Essential for Internet communication

⭐ One-Line Summary

🔹 Logical addressing uses IP addresses to uniquely identify devices and enable data routing across different networks.