Class A

  • Private address space: 0.0.0.0/8 to 127.0.0.0/8
  • Default subnet mask: 255.0.0.0
  • Class A uses a fixed /8 prefix with the 1st octet to indicate the network address and the remaining three octets for host address
  • Number of possible Networks – 127
  • Number of possible Hosts per Network – 16, 777,214

Class B

  • Private address space: 128.0.0.0/16 to 191.255.0.0/16
  • Default subnet mask: 255.255.0.0
  • Class B uses a fixed /16 prefix with two high-order octets to indicate the network address and the remaining two octets for host addresses.
  • Supports the needs of moderate to large size networks with up to 65,000 host addresses per network.
  • Number of possible Networks – 16,384
  • Number of possible Hosts per Network – 65,534

Class C

  • Private address space: 192.0.0.0/24 to 223.255.255.0/24
  • Default subnet mask: 255.255.255.0
  • Class C uses a fixed /24 prefix with the first three octets to indicates the network and the remaining octet for the host addresses
  • Designed to support small network with a maximum of 254 hosts
  • Number of possible Networks – 2,097,152
  • Number of possible Hosts per Network – 254
Class A Addressing Guide
0.0.0.0/8 to 127.0.0.0/8


Here, the Class A Addressing table shows how many host IP addresses we can have for the number of bits borrowed.





    CIDR (Classless Inter-Domain Routing)

    # of Bits Borrowed
    Subnet Mask
    Total # of Subnets
    Total # of Hosts
    Usable # of Hosts
  

  

    /8
    0
    255.0.0.0
    1
    16,777,216
    16,777,214
  

 

    /9
    1
    255.128.0.0
    2
    8,388,608
    8,388,606
  

  

    /10
    2
    255.192.0.0
    4
    4,194,304
    4,194,302
  

  

    /11
    3
    255.224.0.0
    8
    2,097,152
    2,097,150
  

  

    /12
    4
    255.240.0.0
    16
    1,048,576
    1,048,574
  

  

    /13
    5
    255.248.0.0
    32
    524,288
    524,286
  

  

    /14
    6
    255.252.0.0
    64
    262,144
    262,142
  

  

    /15
    7
    255.254.0.0
    128
    131,072
    131,070
  

  

    /16
    8
    255.255.0.0
    256
    65,536
    65,534
  

  

    /17
    9
    255.255.128.0
    512
    32,768
    32,766
  

  

    /18
    10
    255.255.192.0
    1,024
    16,384
    16,382
  

  

    /19
    11
    255.255.224.0
    2,048
    8,192
    8,190
  

  

    /20
    12
    255.255.240.0
    4,096
    4,096
    4,094
  

 

    /21
    13
    255.255.248.0
    8,192
    2,048
    2,046
  

  

    /22
    14
    255.255.252.0
    16,284
    1,024
    1,022
  

  

    /23
    15
    255.255.254.0
    32,768
    512
    510
  

  

    /24
    16
    255.255.255.0
    65,536
    256
    254
  

  

    /25
    17
    255.255.255.128
    131,072
    128
    126
  

  

    /26
    18
    255.255.255.192
    262,144
    64
    62
  

  

    /27
    19
    255.255.255.224
    524,288
    32
    30
  

  

    /28
    20
    255.255.255.240
    1,048,576
    16
    14
  

  

    /29
    21
    255.255.255.248
    2,097,152
    8
    6
  

  

    /30
    22
    255.255.255.252
    4,194,304
    4
    2
Class B Addressing Guide
128.0.0.0/16 to 191.255.0.0/16
Here, the Class B Addressing table shows how many host IP addresses including number of subnets we can have for the number of bits borrowed.





    CIDR (Classless Inter-Domain Routing)

    # of Bits Borrowed
    Subnet Mask
    Total # of Subnets
    Total # of Hosts
    Usable # of Hosts
  

  
  

    /16
    0
    255.255.0.0
    1
    65,536
    65,534
  

  

    /17
    1
    255.255.128.0
    2
    32,768
    32,766
  

  

    /18
    2
    255.255.192.0
    4
    16,384
    16,382
  

  

    /19
    3
    255.255.224.0
    8
    8,192
    8,190
  

  

    /20
    4
    255.255.240.0
    16
    4,096
    4,094
  

 

    /21
    5
    255.255.248.0
    32
    2,048
    2,046
  

  

    /22
    6
    255.255.252.0
    64
    1,024
    1,022
  

  

    /23
    7
    255.255.254.0
    128
    512
    510
  

  

    /24
    8
    255.255.255.0
    256
    256
    254
  

  

    /25
    9
    255.255.255.128
    512
    128
    126
  

  

    /26
    10
    255.255.255.192
    1,024
    64
    62
  

  

    /27
    11
    255.255.255.224
    2,048
    32
    30
  

  

    /28
    12
    255.255.255.240
    4,0966
    16
    14
  

  

    /29
    13
    255.255.255.248
    8,192
    8
    6
  

  

    /30
    14
    255.255.255.252
    16,384
    4
    2
Class C Addressing Guide
192.0.0.0/24 to 223.255.255.0/24
Here, the Class C Addressing table shows how many host IP addresses including number of subnets we can have for the number of bits borrowed.





    CIDR (Classless Inter-Domain Routing)

    # of Bits Borrowed
    Subnet Mask
    Total # of Subnets
    Total # of Hosts
    Usable # of Hosts
  

  
  

    /24
    0
    255.255.255.0
    1
    256
    254
  

  

    /25
    1
    255.255.255.128
    2
    128
    126
  

  

    /26
    2
    255.255.255.192
    4
    64
    62
  

  

    /27
    3
    255.255.255.224
    8
    32
    30
  

  

    /28
    4
    255.255.255.240
    16
    16
    14
  

  

    /29
    5
    255.255.255.248
    32
    8
    6
  

  

    /30
    6
    255.255.255.252
    64
    4
    2