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CIDR: "Classless" Inter-Domain Routing

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• CIDR: Classless Inter-Domain Routing...

  • Classless:

    In CIDR, there are no network classes: No class A Nor class B Etc

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  • Specifying a network domain in CIDR:

    A CIDR IP domain is specified by: a 32 bit IP address a IP network prefix (= number of bits that constitute the network ID) Example: Emory's CIDR IP domain is: 170.140.0.0/16 ^^ IP network prefix The number 16 indicates the first 16 bits is the network ID

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• How the CIDR methods solved the address shortage problem
  • Fact:

    The CIDR Internet domain specification allow you to assign the "rightsize" to an IP network

    Example:

    CIDR Address IP address range covered by CIDR address ================== ========================================== 255.255.255.0/24 from 11111111 11111111 11111111 00000000 to 11111111 11111111 11111111 11111111 ==> from 255.255.255.0 to 255.255.255.255 (= 28 = 256 addresses) 255.255.255.0/23 from 11111111 11111111 11111110 00000000 to 11111111 11111111 11111111 11111111 ==> from 255.255.254.0 to 255.255.255.255 (= 29 = 512 addresses)

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  • History:

    When CIDR was adopted: a large number of companies and universities (including Emory) who owned a class B addresses needed to return their IP domain Some were given smaller IP domains Result: A lot of IP addresses became available for use !!!

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  • Disadvantage of CIDR:

    The number of IP domains also increased Router needed to have more memory (It was OK, by then, the computer memory got much larger and memory prices has has dropped significantly...)