{"id":335,"date":"2017-02-03T07:51:00","date_gmt":"2017-02-03T07:51:00","guid":{"rendered":"https:\/\/opstree.com\/blog\/\/2017\/02\/03\/classless-inter-domain-routing-made-easy\/"},"modified":"2025-11-28T10:57:23","modified_gmt":"2025-11-28T05:27:23","slug":"classless-inter-domain-routing-made-easy","status":"publish","type":"post","link":"https:\/\/opstree.com\/blog\/2017\/02\/03\/classless-inter-domain-routing-made-easy\/","title":{"rendered":"Classless Inter Domain Routing Made Easy"},"content":{"rendered":"
\n
Introduction :<\/div>\n
One day I was working with VPC (Virtual Private Cloud) inside AWS(Amazon Web Services), where I had a need to calculate the CIDR notation of an IP address and subnet combinations.<\/div>\n
I had to use online tools to calculate the Subnets and CIDR every time when I was working with VPC, but I found it interesting that how the network get \u00a0broken into different small Networks. So, finally I decided why not to learn CIDR Methods, and then calculate it by my own side instead of using tools every time.<\/div>\n
<\/div>\n
But the questions that striked in my mind were:<\/div>\n
    \n
  • \n
    What is CIDR ?<\/div>\n<\/li>\n
  • \n
    How CIDR Came into Picture ?<\/div>\n<\/li>\n
  • \n
    What CIDR do ?<\/div>\n<\/li>\n<\/ul>\n
    For Understanding CIDR – (Classless Inter-Domain Routing) few thing need to be cleared before :<\/div>\n

    1. IP Addresses<\/div>\n
    2. Structure of IP Address<\/div>\n
    3. Internet Protocol Address Types<\/div>\n
    4. Classes<\/div>\n
    5. Network Mask<\/div>\n
    6. Subnetting<\/div>\n

    IP Address –<\/h2>\n
    It is the Address of the Computer, Laptop, Printers or even of the Mobile Sets.
    Everyone has some Address, so as these devices also have an Internet Protocol Address (IP Address), also called as Logical Address.<\/div>\n
    In a Network there are many Computers \u2026<\/div>\n
    Network..??<\/div>\n
    A Network is a group of two or more Computers Linked Together.<\/div>\n
    So When there are Many Computers in a Network, We need to uniquely identify each Computer, so there IP ADDRESS works as an Unique Identifier for Computers and Other Devices.<\/div>\n
    For Example : There are Twin Sisters, How we are going to Identify them differently \u00a0
    By their Name that are unique for each of them.<\/div>\n
    Here Name of the Girls are the IP Addresses that will be unique and the two Girls are the two Devices.<\/div>\n

    Structure of IP Address –<\/h2>\n
    Now the Question is How do an IP Address looks like??<\/div>\n
    IP ADDRESS : 192.168.33.10<\/div>\n
    IP ADDRESS is made up of 32-Bit – 8.8.8.8 = (8+8+8+8=32 Bits)<\/div>\n
    A bit (short for binary digit) is the smallest unit of data in a computer.<\/div>\n
    Binary Conversion for 192 :<\/div>\n
    192 :\u00a0\u00a0\u00a0 128\u00a0\u00a0\u00a0 \u00a0 64\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 32\u00a0\u00a0 \u00a0\u00a0 16\u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0 8 \u00a0\u00a0 \u00a0 4 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 2 \u00a0 \u00a0 \u00a0\u00a0\u00a0 1<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01\u00a0 \u00a0\u00a0 \u00a0\u00a0 1 \u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0 0 \u00a0\u00a0\u00a0 \u00a0 \u00a0 0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 0\u00a0 \u00a0 \u00a0\u00a0 0\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 0\u00a0 \u00a0 \u00a0 \u00a0\u00a0 0<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Bit 1 \u00a0\u00a0\u00a0Bit 2 \u00a0\u00a0\u00a0Bit 3 \u00a0\u00a0Bit 4 \u00a0\u00a0\u00a0\u00a0Bit 5 \u00a0\u00a0\u00a0Bit 6 \u00a0\u00a0Bit 7 \u00a0\u00a0\u00a0\u00a0Bit 8 \u00a0\u00a0\u00a0– Total Bit = 8<\/div>\n
    128+64 = 192
    So, 0\u2019s for Other and 1 for the Number whose sum will be 192<\/div>\n
    Binary Conversion for 168 :<\/div>\n
    168 : \u00a0\u00a0\u00a0128\u00a0\u00a0 \u00a0\u00a0 64 \u00a0 \u00a0\u00a0\u00a0 32\u00a0 \u00a0 \u00a0 \u00a0\u00a0 16 \u00a0 \u00a0 \u00a0 8 \u00a0 \u00a0 \u00a0 \u00a0\u00a0\u00a0 4 \u00a0 \u00a0 \u00a0\u00a0\u00a0 2 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 1<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Bit 1 \u00a0\u00a0\u00a0Bit 2 \u00a0\u00a0\u00a0Bit 3 \u00a0\u00a0Bit 4 \u00a0\u00a0\u00a0\u00a0Bit 5 \u00a0\u00a0\u00a0Bit 6 \u00a0\u00a0Bit 7 \u00a0\u00a0\u00a0\u00a0Bit 8 – Total Bit = 8<\/div>\n
    Binary Conversion for 33 :<\/div>\n
    \u00a0\u00a033 : \u00a0\u00a0128\u00a0\u00a0 \u00a0 \u00a0\u00a0 64\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 32\u00a0\u00a0 \u00a0 \u00a0\u00a0 16\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 8\u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0 4\u00a0 \u00a0 \u00a0 \u00a0\u00a0 2\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 1<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Bit 1 \u00a0\u00a0\u00a0Bit 2 \u00a0\u00a0\u00a0Bit 3 \u00a0\u00a0Bit 4 \u00a0\u00a0\u00a0\u00a0Bit 5 \u00a0\u00a0\u00a0Bit 6 \u00a0\u00a0Bit 7 \u00a0\u00a0\u00a0\u00a0Bit 8 – Total Bit = 8<\/div>\n
    Binary Conversion for 10 :<\/div>\n
    10 : \u00a0\u00a0\u00a0\u00a0128\u00a0 \u00a0 \u00a0\u00a0 64 \u00a0 \u00a0 \u00a0 32\u00a0\u00a0 \u00a0 \u00a0 \u00a0 16\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 8 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 4 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 2 \u00a0 \u00a0 \u00a0\u00a0 \u00a0 1<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a01 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a00<\/div>\n
    \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Bit 1 \u00a0\u00a0\u00a0Bit 2 \u00a0\u00a0\u00a0Bit 3 \u00a0\u00a0Bit 4 \u00a0\u00a0\u00a0\u00a0Bit 5 \u00a0\u00a0\u00a0Bit 6 \u00a0\u00a0Bit 7 \u00a0\u00a0\u00a0\u00a0Bit 8 – Total Bit = 8<\/div>\n
    8.8.8.8 – total of 32 Bit.<\/div>\n
    Dotted Decimal Notation : In dot form 4 Sections are called as OCTETS – Vendor Neutral Term for Bytes.<\/div>\n
    Let a IP Be : 200.10.20.30<\/div>\n
    Inside a Network : 200.10.20 – will remain same and 30 will be unique for each.<\/div>\n

    Type of IP Address –<\/h2>\n
      \n
    1. \n
      Assignment Method<\/div>\n<\/li>\n
    2. \n
      Classes : 1) Classful
      \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a02) Classless<\/div>\n<\/li>\n
    3. \n
      Public \/ Private<\/div>\n<\/li>\n
    4. \n
      Version<\/div>\n<\/li>\n<\/ol>\n

      Assignment Methods :<\/h3>\n
      Assignment Method is method that defines how to assign an IP address to a Device.<\/div>\n
      IP Address can be assigned in two ways<\/div>\n
      1) Static IP Address<\/div>\n
      Static IP Address is the IP Address in which configuration is done Manually and is used in small networks.<\/div>\n
      2) Dynamic IP Address<\/div>\n
      Dynamic IP Address is the IP Address in which the configuration is done by the Computer Interface or by the Host Interface – DHCP (Dynamic Host Configuration Protocol)<\/div>\n
      — Configuration is Automatic–<\/div>\n

      Classes :<\/h2>\n
      classes define that in an IP, How much part will be for Network and How much is for Host.<\/div>\n
      There are 2 types of classes in IP Addressing :<\/div>\n
        \n
      1. \n
        Classful<\/div>\n<\/li>\n
      2. \n
        Classless<\/div>\n<\/li>\n<\/ol>\n
        CLASSFUL : IP Address are divided into 5 Classes;<\/div>\n
        Class A : 0 – 126 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0N.H.H.H \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Assigned for Large Organization<\/div>\n
        127\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0 \u00a0\u00a0\u00a0 N.H.H.H\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Assigned for the Loopback<\/div>\n
        Class B : 128 – 191 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0N.N.H.H \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Assigned for Medium Companies<\/div>\n
        Class C : 192 – 223 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0N.N.N.H \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Assigned for Small Organizations<\/div>\n
        Class D : 224 – 239 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Assigned for Multicasting<\/div>\n
        Class E : 240 – 255 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0Assigned for Experimental Purpose<\/div>\n
        \n
        CLASSLESS : Classless addressing is an \u00a0IP address where a subnet mask does not define its class. \u00a0Subnet mask can be anywhere between bit 0 and bit 31.<\/div>\n
        CLASS A IP ADDRESS :<\/div>\n
        Range of Class A IP Address : \u00a00.0.0.0 – 127.255.255.255<\/div>\n
        Network ID : 8 Bit<\/div>\n
        Host ID : 24 Bit (8+8+8)<\/div>\n
          \n
        • \n
          IP Address begins with 0,First Bit will always be Zero<\/div>\n<\/li>\n
        • \n
          7 Remaining Bits in Network part : Only 128 Possible class A Network<\/div>\n<\/li>\n
        • \n
          24 Bits in Local Part : Over 16 million hosts per Class A Network<\/div>\n<\/li>\n
        • \n
          All class A network parts are assigned or reserved.<\/div>\n<\/li>\n<\/ul>\n
          <\/div>\n
          \n\n\n\n\n\n<\/colgroup>\n\n\n
          \n
          Network ID(N)<\/div>\n<\/td>\n
          		\n
          Host ID(H)<\/div>\n<\/td>\n
          		\n
          Host ID(H)<\/div>\n<\/td>\n
          		\n
          Host ID(H)<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n
          0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a07 8 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a031<\/div>\n
          0NNNNNNN \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0. \u00a0\u00a0\u00a0\u00a0\u00a0HHHHHHHH \u00a0\u00a0\u00a0\u00a0. \u00a0\u00a0\u00a0\u00a0\u00a0HHHHHHHH \u00a0\u00a0. \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0HHHHHHHH<\/div>\n
          In Binary :<\/div>\n
          Class A starts from : 00000000.00000000.00000000.00000000<\/div>\n
          Class A ends at \u00a0\u00a0\u00a0\u00a0\u00a0: 01111111.11111111.11111111.11111111<\/div>\n
          In Decimal :<\/div>\n
          Class A IP Address is from 0.0.0.0 to 127.255.255.255<\/div>\n
          Number of Networks : 2^7 = 128<\/div>\n
          Number of Hosts : 2^24<\/div>\n
          SOME EXCEPTIONS IN CLASS A : Cannot be assigned to host<\/div>\n
          0.0.0.0 : For Self check – Represent Default Network or M<\/div>\n
          0.255.255.255 : For Self check – Represent Default Network or My IP<\/div>\n
          127.0.0.0 : Loop Back Address Range : solve NIC Problem<\/div>\n
          127.255.255.255 : Loop Back Address Range : solve NIC Problem<\/div>\n
          <\/div>\n
          \n
          CLASS B IP ADDRESS :<\/div>\n
          Range of Class B IP Address : 128.0.0.0 – 191.255.255.255<\/div>\n
          Network ID : 16 Bit(8+8)<\/div>\n
          Host ID : 16 Bit (8+8)<\/div>\n