Professor Messor Net+ 1.7.1 - Classful Subnetting

Professor Messor Net+ 1.7.1

Class A Network/Hosts Bits & Default Subnet Mask

• 8 Network Bits

• 24 Hosts Bits

• Default Subnet Mask: 255.0.0.0

Class B Network/Hosts Bits & Default Subnet Mask

• 16 Network Bits

• 16 Hosts Bits

• Default Subnet Mask: 255.255.0.0

Class C Network/Hosts Bits & Default Subnet Mask

• 24 Network Bits

• 8 Hosts Bits

• Default Subnet Mask: 255.255.255.0

Class A

• Leading Bits: 0xxx (0-127)

• Network Bits: 8

• Remaining Bits: 24

• Number of Networks: 128

• Hosts Per Network: 16,777,214

• Default Subnet Mask: 255.0.0.0

Class B

• Leading Bits: 10xx (128-191)

• Network Bits: 16

• Remaining Bits: 16

• Number of Networks: 16,384

• Hosts Per Network: 65,534

• Default Subnet Mask: 255.255.0.0

Class C

• Leading Bits: 110x (192-223)

• Network Bits: 24

• Remaining Bits: 8

• Number of Networks: 2,097,152

• Hosts Per Network: 254

• Default Subnet Mask: 255.255.0.0

Class D

• Class D is for multicast addressing

• Leading Bits: 1110 (224-239)

Class E

• Class E addresses are reserved

• Leading Bits: 1111 (240-255)

The Construction of a Subnet

• Network Address

  • This is the first IP address of a subnet

  • To calculate this, set all host bits of 0 (0 decimal)

• First usable host address

  • One number higher than the network address

• Network Broadcast Address

  • This the last IP address of a subnet

  • To calculate this, set all host bits to 1 (255 decimal)

• Last usable host address

  • This is one number lower than the broadcast address