🌐 What is a Subnet Mask?

📖 Definition

A Subnet Mask is a 32-bit number used to divide an IP address into:

• Network ID (network portion)
• Host ID (device portion)

🧠 Simple Meaning

👉 Subnet mask tells:
Which part is network and which part is host

📍 Example

IP Address: 192.168.1.10
Subnet Mask: 255.255.255.0

👉 Meaning:

• Network → 192.168.1
• Host → 10

🔢 How Subnet Mask Works (Binary Concept)

Subnet mask uses:

• 1 → Network bits
• 0 → Host bits

📊 Example in Binary

Subnet Mask: 255.255.255.0

Binary:

11111111.11111111.11111111.00000000

👉 First 24 bits = Network
👉 Last 8 bits = Host

📌 Common Default Subnet Masks

🧠 What is CIDR?

📖 Definition

CIDR (Classless Inter-Domain Routing) is a method of representing IP addresses using a slash notation (/).

🧠 Simple Meaning

👉 CIDR tells how many bits are used for network

📍 Example

192.168.1.0/24

👉 /24 means:

• First 24 bits = Network
• Remaining bits = Host

🔄 Subnet Mask ↔ CIDR Conversion

⚡ Why Subnetting is Needed?

• Efficient use of IP addresses
• Better network management
• Improved security
• Reduced network traffic

🧠 Easy Trick to Remember CIDR

👉 Count number of 1s in subnet mask

Example:

255.255.255.0
→ 24 ones → /24

🎯 Key Exam Points

• Subnet mask divides network & host
• CIDR uses “/” notation
• 1 = Network, 0 = Host
• /24 = 255.255.255.0
• Used in subnetting

🎓 Interview-Ready Answers

❓ What is a subnet mask?

A subnet mask is a 32-bit number used to separate the network portion and host portion of an IP address.

❓ What is CIDR?

CIDR is a method of representing IP addresses using slash notation to indicate the number of bits used for the network portion.

❓ Difference between Subnet Mask and CIDR?

Subnet mask is written in dotted decimal format, while CIDR is a shorthand representation using slash notation.

🧠 Memory Trick

👉 Mask = Division
👉 CIDR = Count of Network Bits

👉 Explore IP Addressing and Subnetting concepts

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