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CIDR

Nov 05, 20233 min read

CIDR

  • Classless Inter-Domain Routing
  • A Longest Prefix Match

Class A: Allows 2^24 host addresses on the network. The starting host address is 0.0.0.0 and the ending address is 127.0.0.0. These networks use the 255.0.0.0 subnet mask, or /8 CIDR notation.

Class B: Allows 2^16 host addresses on the network. The starting host address is 128.0.0.0 and the ending address is 191.255.0.0. These networks use the 255.255.0.0 subnet mask, or /16 CIDR notation.

Class C: Allows 2^8 host addresses on the network. The starting host address is 192.0.0.0 and the ending address is 223.255.255.0. These networks use the 255.255.255.0 subnet mask, or /24 CIDR notation.

Classful IP

Class A

  • Public IP Range: 0.0.0.0 to 127.255.255.255
    • First octet value range from 0 to 127
  • Private IP Range: 10.0.0.0 to 10.255.255.255 (See Private IP Addresses below for more information)
  • Subnet Mask: 255.0.0.0 (8 bits)
  • Number of Networks: 126
  • Number of Hosts per Network: 16,777,214

Class B

  • Public IP Range: 128.0.0.0 to 191.255.0.0
    • First octet value range from 128 to 191
  • Private IP Range: 172.16.0.0 to 172.31.255.255 (See Private IP Addresses below for more information)
  • Subnet Mask: 255.255.0.0 (16 bits)
  • Number of Networks: 16,382
  • Number of Hosts per Network: 65,534

Class C

  • Public IP Range: 192.0.0.0 to 223.255.255.0
    • First octet value range from 192 to 223
  • Private IP Range: 192.168.0.0 to 192.168.255.255 (See Private IP Addresses below for more information)
  • Special IP Range: 127.0.0.1 to 127.255.255.255 (See Special IP Addresses below for more information)
  • Subnet Mask: 255.255.255.0 (24 bits)
  • Number of Networks: 2,097,150
  • Number of Hosts per Network: 254

Class D

  • Range: 224.0.0.0 to 239.255.255.255
    • First octet value range from 224 to 239
  • Number of Networks: N/A
  • Number of Hosts per Network: Multicasting
  • IGMP

Class E

  • Range: 240.0.0.0 to 255.255.255.255
    • First octet value range from 240 to 255
  • Number of Networks: N/A
  • Number of Hosts per Network: Research/Reserved/Experimental
Class A
  0.  0.  0.  0 = 00000000.00000000.00000000.00000000
127.255.255.255 = 01111111.11111111.11111111.11111111
                  0nnnnnnn.HHHHHHHH.HHHHHHHH.HHHHHHHH

Class B
128.  0.  0.  0 = 10000000.00000000.00000000.00000000
191.255.255.255 = 10111111.11111111.11111111.11111111
                  10nnnnnn.nnnnnnnn.HHHHHHHH.HHHHHHHH

Class C
192.  0.  0.  0 = 11000000.00000000.00000000.00000000
223.255.255.255 = 11011111.11111111.11111111.11111111
                  110nnnnn.nnnnnnnn.nnnnnnnn.HHHHHHHH

Class D
224.  0.  0.  0 = 11100000.00000000.00000000.00000000
239.255.255.255 = 11101111.11111111.11111111.11111111
                  1110XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX

Class E
240.  0.  0.  0 = 11110000.00000000.00000000.00000000
255.255.255.255 = 11111111.11111111.11111111.11111111
                  1111XXXX.XXXXXXXX.XXXXXXXX.XXXXXXXX

Private IP Addresses

  • Class A Private Range: 10.0.0.0 to 10.255.255.255

  • Class B Private APIPA Range: 169.254.0.0 to 169.254.255.255

    • Automatic Private IP Addressing (APIPA) is a feature with Microsoft Windows-based computers to automatically assign itself an IP address within this range if a Dynamic Host Configuration Protocol (DHCP) server is not available on the network. A DHCP server is a network device that is responsible for assigning IP addresses to devices on the network.
    • At your home, your Internet modem or router likely provides this functionality. In your work place, a Microsoft Windows Server, a network firewall, or some other specialized network device likely provides this functionality for the computer at your work environment.

  • Class B Private Range: 172.16.0.0 to 172.31.255.255

  • Class C Private Range: 192.168.0.0 to 192.168.255.255

  • Ethernet Numbers

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