1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Another subnetting guide

Discussion in 'General Cisco Certifications' started by datarunner, Aug 6, 2008.

  1. datarunner

    datarunner Byte Poster

    245
    1
    24
    hi all

    after struggling with subnetting for a while i have created a simple guide on how to do it easily and quickly. i have given some scenarios as to where subnetting might be used.

    im no guru on the subject, i just wanted to share wot ive learned so that it sticks

    you are welcome to comment or add to it if u like

    view it here
     
    Certifications: A+, N+, MCP 210, 270, HNC Networking
    WIP: MCSA
  2. datarunner

    datarunner Byte Poster

    245
    1
    24
    hi all

    just wanna verify that my basic info is correct

    Below are some scenarios which will help you to learn subnetting more easily

    Scenario 1 - Given a network address and subnet mask - How many subnets can you have and how many hosts per subnet.
    Here we are given the address of: 172.16.0.0 /22

    First we list the mask then the address in binary:

    11111111 11111111 11111100 00000000 - Subnet mask

    10101100 00010000 00000000 00000000 - Address

    To calculate the number of subnets we total up the extra bits we are using in the mask, in this case its 6

    So as we are using 6 extra bits for the mask we can use the formula:

    2 to the power of 6-2 or 2x2x2x2x2x2 = 64-2 =62 subnets

    To calculate the number of hosts per subnet we total up the bits available for hosts, in this case its 10

    So as we are using 10 bits for the host we can use the formula:

    2 to the power of 10-2 or 2x2x2x2x2x2x2x2x2x2 = 1024-2 1022 hosts per subnet

    Point to remember 2 to the power of bits used for either mask or hosts minus 2 will give you either the number of subnets or hosts per subnet



    Scenario 2 - Given a network address calculate the customers requirements or subnets and hosts per network
    Here we are given the address of: 172.16.0.0 and require 6 departments with 2000 hosts per department

    First we list the mask then the address in binary:

    11111111 11111111 00000000 00000000 - Subnet mask

    10101100 00010000 00000000 00000000 - Address

    As the first two octets are the default for this address type (255.255.0.0.) we go to the 3rd octet and start using bits there.

    using 1 bit will give us 2 to the power of 1 or 2x1 =2-2 =0 Not enough

    using 2 bits will give us 2 to the power of 2 or 2x2=4-2 =2 Not enough

    using 3 bits will give us 2 to the power of 3 or 2x2x2=8-2 = 6 Enough

    As we used 3 bits there are 13 bits left (5 from one octet 8 from the other) for hosts so 2 to the power of 13 = 8192-2 =8190 Enough for our hosts



    Scenario 3 - Given a network address and subnet mask list the valid subnets
    Here we are given the address of: 172.16.0.0 and subnet mask of 255.255.224.0

    First we list the mask then the address in binary:

    11111111 11111111 11100000 00000000 - Subnet mask

    10101100 00010000 00000000 00000000 - Address

    As we are using 3 extra bits for the mask we look at the right most bit in the binary table, in this case its 32 so our networks will increment in numbers of 32, 0 (not used), 32, 64, 96 etc until the 3 bits or 3 1s are full totallying to 224.

    all comments, suggestions, improvements welcome
     
    Certifications: A+, N+, MCP 210, 270, HNC Networking
    WIP: MCSA

Share This Page

Loading...