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Subnetting

Discussion in 'Network+' started by Boycie, Jun 6, 2005.

  1. Boycie
    Honorary Member

    Boycie Senior Beer Tester

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    Hi Guys,

    As an example, if we wanted to subnet our Class C network then depending on how many IP address' we wanted per subnet then do you:

    subtract the number of IP address from 254?
    For example, If we wanted 30 IP address' per subnet that would give us a subnet of 255.255.255.224 (254-30=224)

    255.255.255.0 would be the first subnet network number
    255.255.255.1 would be the first address
    255.255.255.31 would be the broadcast address
    with everything between 1 and 30 availible for client address'

    255.255.255.32 would be the second subnet and so on....
    giving 8 subnet's with 30 IP address

    I hope that a) you guy's understand my poor way of explanation (this is how my mind has concepted it at the mo!) b)my theory is right! :blink
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT
  2. Phoenix
    Honorary Member

    Phoenix 53656e696f7220 4d6f64

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    Well your theory works in this example, because it just happens to be a number that works
    however I don't believe it would work for every random number you throw at it

    Subnets as far as I recall require the bits to be set in sequence

    for instance you can have a subnet of .224 (Binary = 11100000)
    but you couldnt have a subnet of .226 (Binary = 11100010)

    30 (or in essence, 32) just happens to be one of those power of 2 numbers that we know and love so well

    Valid subnets follow the binary sequence from (10000000 to 11111110) and even 11111110 requires special software understanding to make use of

    remember the sequence needs to be maintained, you cant have a gap in it or things that utilise subnets will get confused

    10000000 = 128
    11000000 = 192
    11100000 = 224
    11110000 = 240
    11111000 = 248
    11111100 = 252
    11111110 = 254

    You have to learn how to calculate the appropriate subnet mask for the given situation, not the precise number of hosts, as its often not possible, so if you required 22 IP addresses you would probably choose the same .224 subnet as the closest match with 30 hosts per subnet, as the next match in the sequence (240) only provides for 14 IP addresses, thus is of no use to your situation

    its not very clear, subnetting is a beast of a subject, and I'm far from a master of the subject, let alone a good teacher of it, hope it helps a little
     
    Certifications: MCSE, MCITP, VCP
    WIP: > 0
  3. Boycie
    Honorary Member

    Boycie Senior Beer Tester

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    Thanks again Ryan :D
    It looks like as far as the Network + exam goes as long as I have a good basic understanding I should be just fine :rolleyes:
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT
  4. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

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    When I was studying for my CCNA, I used "Learn to Subnet". It really made a difference. Click the link below to see for yourself.

    http://www.learntosubnet.com/
     
    Certifications: A+ and Network+
  5. Boycie
    Honorary Member

    Boycie Senior Beer Tester

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    Thanks Trip. What a cracking link :thumbleft
     
    Certifications: MCSA 2003, MCDST, A+, N+, CTT+, MCT

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