Class B IP Analysis

Nerd Cafe | نرد کافه

Let’s do a step-by-step IP analysis of:

IP: 172.16.1.20/16

We will find:

1. Network IP

2. Broadcast IP

3. First IP (usable)

4. Last IP (usable)

5. Number of available IPs (hosts)

6. Subnet mask

Write IP in binary

Break down each octet to binary:

Octet	Decimal	Binary
1	172	10101100
2	16	00010000
3	1	00000001
4	20	00010100

Full IP in binary:

10101100.00010000.00000001.00010100

1. Subnet Mask in binary

CIDR = /16

Means:

• 16 bits for network (all 1’s)

• 16 bits for host (all 0’s)

Octet	Decimal	Binary
1	255	11111111
2	255	11111111
3	0	00000000
4	0	00000000

Subnet mask:

255.255.0.0

Binary:

11111111.11111111.00000000.00000000

Meaning:

• First 24 bits = Network part

• Last 8 bits = Host part

2. Find Network Address

Rule:

Network Address = IP AND Subnet Mask

IP in binary:

10101100.00010000.00000001.00010100

Subnet Mask:

11111111.11111111.00000000.00000000

Bitwise AND:

10101100.00010000.00000000.00000000

Convert to decimal:

Octet	Binary	Decimal
1	11000000	172
2	00010000	16
3	00000000	0
4	00000000	0

Network Address

172.16.0.0

3. Find Broadcast Address

Rule:

Broadcast = Network Address with all host bits = 1

• Network bits (first 24) stay the same

• Host bits (last 8) all 1

Binary:

10101100.00010000.11111111.11111111

Decimal:

Octet	Binary	Decimal
1	10101100	172
2	00010000	16
3	11111111	255
4	11111111	255

Broadcast Address

172.16.255.255

4. First Usable IP

Rule:

First Usable = Network Address + 1

• Network Address: 172.16.0.0

• Add 1 to last octet:

Network Address:

172.16.0.0

First IP in Binary:

10101100.00010000.00000000.00000001

First Usable IP

172.16.0.1

5. Last Usable IP

Rule:

Last Usable = Broadcast - 1

• Broadcast Address: 172.16.255.255

• Subtract 1 from last octet:

Broadcast Address:

172.16.255.255

Last IP in Binary:

10101100.00010000.11111111.11111110

Last Usable IP

172.16.255.254

6. Number of Usable IPs

Rule:

$$Usable\;IPs=2^{host\;bits}-2$$

• Host bits = 16 (since /16)

• Calculation:

2^16 = 65,536
65,536 - 2 = 65,534

Number of usable IP

65,534

Final Answer in Table (with Binary)

Item	Decimal	Binary
Subnet Mask	255.255.0.0	11111111.11111111.00000000.00000000
Network Address	172.16.0.0	10101100.00010000.00000000.00000000
Broadcast Address	172.16.255.255	10101100.00010000.11111111.11111111
First Usable IP	172.16.0.1	10101100.00010000.00000000.00000001
Last Usable IP	172.16.255.254	10101100.00010000.11111111.11111110
Number of Usable IPs	65,534	(2^16)-2

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Keywords

Network IP , Broadcast IP , First IP (usable) , Last IP (usable) , Number of available IPs (hosts) , Subnet mask , Nerd Cafe , نرد کافه

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