IP Subnetting

1. IP Subnetting Shahzad Rashid NOC Executive Engineer (TXN) Telenor Pakistan 2. Contents

• IP Classes

• Why Subnetting

• Subnetting for Networks

• Subnetting for Hosts

3.

• IP Classes:

• Class A: 1-126 (16 Million Hosts on 127 Networks)

• Class B: 128-191 (65000 Hosts on 16000 Networks)

• Class C: 192-223 (254 Hosts on 2 Million Networks)

• Class D: 224-239 (Reserved for Multicast Groups)

• Class E: 240-254 (For Future use and R & D)

• Loop Back Address: 127.x.x.x (Reserved for Loopback Tests)

• .1/.2 are usually used as Gateway Addresses

• The last address e.g. .255 is used as Broadcast Address

• Why Subnetting:

• To preserve Public IPv4 Addresses

4. Subnetting for Networks

• .

• Step 1: Convert the Number of Networks to Binary

• Step 2: Reserve bits in Subnet Mask according to the Number of Networks Converted to Binary (From Left to Right)

• Step 3: Use the Last Reserved bit to find your Network Ranges

5. Practice Scenario

• .

• Subnetting for 5 Networks using Class C IP Address: 192.168.1.0

• Default Class C Mask: 255.255.255.0

• Step 1: Convert required Networks to Binary

• 128 64 32 16 8 4 2 1

• 0 0 0 0 0 1 0 1

• Bit 1 and 3 are Turned ON. That makes a total of 5

• Now Count from Right to Left and see how far is the last bit Turned ON

• 3 is the count from Right to Left

6. Practice Scenario (Contd…)

• .

• Step 2:

• Subnet mask: 255.255.255.0

• Reserve 3 bits in the Fourth Octet of Subnet Mask from Left to Right (Turn them ON and turn OFF the remaining bits)

• 255 255 255 0

• 11111111 11111111 11111111 000000000

• 11111111 11111111 11111111 111 000000

• First 3 Bits of the Last (Fourth) Octet Reserved

• Subnet Mask comes out to be : 255.255.255.224

• This is the Subnet Mask for 5 Networks

7. Practice Scenario (Contd…)

• .

• Step 3:

• 255 255 255 0

• 11111111 11111111 11111111 000000000

• 11111111 11111111 11111111 111 000000

• Refer to the Last Octet

• 128 64 32 16 8 4 2 1

• 1 1 1 0 0 0 0 0

• Starting from Left to Right notice the last bit Turned ON

• Last bit Turned ON is 32

• Network Ranges will be determined using 32

8. Practice Scenario (Contd…)

• .

• Step 3 (Contd…):

• Network Ranges (The best possible utilization of IP for 5 Networks)

• 1. 192.168.1.1 ----- 192.168.1.31

• 2. 192.168.1.32 ----- 192.168.1.63

• 3. 192.168.1.64 ----- 192.168.1.95

• 4. 192.168.1.96 ----- 192.168.1.127

• 5. 192.168.1.128 ----- 192.168.1.159

• 6. 192.168.1.160 ----- 192.168.1.191

• 7. 192.168.1.192 ----- 192.168.1.223

• These are the 7 Seven Network Ranges which is the most appropriate Subnetting for 5 Networks without misusing the IP’s

9. Subnetting for Hosts

• .

• Step 1: Convert the Number of Hosts to Binary

• Step 2: Reserve bits in Subnet Mask according to the Number of Hosts Converted to Binary (From Right to Left)

• Step 3: Use Last Reserved bit to find your Network Ranges

10. Practice Scenario

• .

• Subnetting for 50 Hosts using Class C IP Address: 192.168.1.0

• Default Class C Mask: 255.255.255.0

• Step 1: Convert required Networks to Binary

• 128 64 32 16 8 4 2 1

• 0 0 1 1 0 0 1 0

• Bit 2, 5 and 6 are Turned ON. That makes a total of 50

• Now Count from Left to Right and see how far is the last bit Turned ON

• 6 is the count from Right to Left

11. Practice Scenario (Contd…)

• .

• Step 2:

• Subnet mask: 255.255.255.0

• Reserve 6 bits in the Fourth Octet of Subnet Mask from Right to Left (Turn them OFF and turn ON the remaining bits)

• 255 255 255 0

• 11111111 11111111 11111111 000000000

• 11111111 11111111 11111111 11 0000000

• Last 6 Bits of the Last (Fourth) Octet Reserved

• Subnet Mask comes out to be : 255.255.255.192

• This is the Subnet Mask for 50 Hosts

12. Practice Scenario (Contd…)

• .

• Step 3:

• 255 255 255 0

• 11111111 11111111 11111111 000000000

• 11111111 11111111 11111111 11 0000000

• Refer to the Last Octet

• 128 64 32 16 8 4 2 1

• 1 1 0 0 0 0 0 0

• Starting from Left to Right notice the last bit Turned ON

• Last bit Turned ON is 64

• Network Ranges for 50 Hosts will be determined using 64

13. Practice Scenario (Contd…)

• .

• Step 3 (Contd…):

• Network Ranges (The best possible utilization of IP for 50 Hosts)

• 1. 192.168.1.1 ----- 192.168.1.63

• 2. 192.168.1.64 ----- 192.168.1.127

• 3. 192.168.1.128 ----- 192.168.1.191

• 4. 192.168.1.192 ----- 192.168.1.255

• Each Network Range can have around 60-61 Hosts each, which is the best possible Subnetting for 50 Hosts

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