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The way I subnet

Discussion in 'General Cisco Certifications' started by HaDeS666, Aug 28, 2008.

  1. HaDeS666

    HaDeS666 Bit Poster

    The way I subnet: Takes around 30 seconds (if that) - with practice! :D

    I have seen some stupid subnetting questions :oops: and thought I'd offer they way I do it to try and help.

    Before you try and learn how to subnet you need to learn binary and the different classes of addresses.

    Forget magic numbers and special tables, if you know binary it's easy, trust me.

    Assumming the ip subnet zero command is in use, we will find the network address, broadbast address and address range. with a mask of

    Prefix notion: = /26

    In the mask you always ignore the 255 and the 0 part so we use the 192 part( 4th octet )in the mask and the address.

    192 in binary is
    128 64 32 16 8 4 2 1
    1 1 0 0 0 0 0 0

    What ever the last one is in the mask 64 in this case, this is the number the subnet go up by:

    Network number: 0 range: 0-62 BC Address: 63
    Network number: 64 range: 65-126 BC Address: 127
    Network number 128 range: 129-190 BC Address: 191
    Network number 192 range: 193-254 BC Address: 255
    Network number 256 (not valid as greater than 255)

    Therefore as 192 in the mask is the 4th octet we use the 4th octet in the address: 150

    From the above find what number is below 150, 150 is between 128 and 192 therefore: /26

    Network number /26
    range: -
    Broadcast Address:

    After a bit practice as soon as you see the mask, you know the multiples of the subnets.
    They can only be 128, 64, 32, 16, 8, 4, 2 or 1.. Look familiar don't they. :rolleyes:
    Certifications: A+ and CCNA
    WIP: MCSA then onto MCSE
  2. -Mercury-

    -Mercury- Byte Poster

    Good post, thanks for sharing.

    I'm going to start on my CCNA as soon as I get some of the lower level certs out of the way.
    Certifications: MCSA|MCDST|A+|Net+

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