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Newbie Question -Subnet Mask

Discussion in 'A+' started by tallpaul, Jan 16, 2008.

  1. tallpaul

    tallpaul Bit Poster

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    I have just finished reading through the big fat Mike meyers book - which i found to be well-written and easy to read, by the way.
    The only concept i'm really having trouble with is a Subnet mask.Could somebody please give a plain english description of its meaning and application in the real world.I think i understand it - just ,but could do with some clarification. Thanks!
     
    Certifications: Nothing spoddy,all electrickery so far
    WIP: a+
  2. hbroomhall

    hbroomhall Petabyte Poster Gold Member

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    How good is your binary arithmetic and your logic? :biggrin

    An IP address is a 32 bit number. It is split into two parts, one part being the number of the network it is on, the other part is the number of the machine on that network.

    The big question is - how do you know which part is which?

    This is where the netmask comes in. By convention the most significant part of the IP address is the network, and the least significant is the machine number. So finding which part is which comes down to finding the boundary between the two parts.

    Now the binary maths and logic bit - if you 'binary AND' the netmask with the IP address you are left with the network part.

    Hope this helps.

    Harry.
     
    Certifications: ECDL A+ Network+ i-Net+
    WIP: Server+
  3. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

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    I've stopped trying to explain it as it involves quite a bit of typing...uh, keyboarding. If you just want to understand what a subnet mask is (which is all you really need to know for the Network+ exam), try these links (and remember, Google is your friend):

    http://ask-leo.com/what_is_a_subnet_mask.html

    http://compnetworking.about.com/od/workingwithipaddresses/a/subnetmask.htm

    If you are interesting in learning how to subnet a network (which you *don't* need to know for the Network+ exam but will need to know if you plan to do any actual serious networking), I highly recommend this site. It taught me enough about subnetting to get me through the CCNA exam:

    http://www.learntosubnet.com/
     
    Certifications: A+ and Network+
  4. nXPLOSi

    nXPLOSi Terabyte Poster

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    I'll try and help out here as well, in more basic terms as i've only really learnt about subnets myself over the last few months.

    An example, a subnet of 255.0.0.0 means that the first part of the IP is the Network part, and the following 3 parts are the machine.

    So, if we had an IP of 15.192.101.45, the 15 is the Network part and 192.101.45 is the machine part. Thats a class A address.

    Lets say for a class C address, we could have an IP of 193.156.101.45 and a subnet mask of 255.255.255.0. In this instance, the first 3 parts are the Network, and the last part is the Machine.

    Thats the basics, but as Trip said subnetting is a whole different ball game, and gets quite complicated. As long as you understand what I've said, thats plenty for the A+.

    Feel free to correct any mistakes I may of made here guys 8)
     
    Certifications: A+, Network+, Security+, MCSA 2003 (270, 290, 291), MCTS (640, 642), MCSA 2008
    WIP: MCSA 2012
  5. r.h.lee

    r.h.lee Gigabyte Poster

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    tallpaul,

    Do you either work with a lot of people or live with people?
     
    Certifications: MCSE, MCP+I, MCP, CCNA, A+
    WIP: CCDA
  6. JonGlory

    JonGlory Byte Poster

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    Subnet mask determines the network and host portion of a IP address.

    If a subnet mask (i.e 255.255.0.0) was to written left to right in binary

    11111111.11111111.00000000.00000000

    And a ip address(192.168.0.12) was to be written in binary

    11000000.10101000.00000000.00001100

    By anding these address together, you would have the following address

    11000000.10101000.00000000.00000000

    In decimal 192.168.0.0, this would be the network address.
     
    WIP: LIFE
  7. tallpaul

    tallpaul Bit Poster

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    thanks a lot everyone.It was the "ask-leo" link that explained it the best for me.
     
    Certifications: Nothing spoddy,all electrickery so far
    WIP: a+
  8. tallpaul

    tallpaul Bit Poster

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    Strange question, no i don't work with a lot of people & i live with my wife. Why do you ask?
     
    Certifications: Nothing spoddy,all electrickery so far
    WIP: a+
  9. tripwire45
    Honorary Member

    tripwire45 Zettabyte Poster

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    I'll echo tallpaul's question. What does this have to do with anything?
     
    Certifications: A+ and Network+
  10. TimoftheC

    TimoftheC Kilobyte Poster

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    I suspect that r.h. was planning to explain it with a real life example - just waiting to see what it is :D
     
    Certifications: A+; Network+
    WIP: MCDST???
  11. JonGlory

    JonGlory Byte Poster

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    Maybe his house number being the network address and the people living in the house being the host address.

    Post man delivers to the house address/network address, host picks up letter with his name on it/host address.

    Im bored as you can guess :)
     
    WIP: LIFE
  12. r.h.lee

    r.h.lee Gigabyte Poster

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    tallpaul,

    Can you imagine if all of your co-workers, bosses, and the entire company worked in the same room in the same office?
     
    Certifications: MCSE, MCP+I, MCP, CCNA, A+
    WIP: CCDA
  13. tallpaul

    tallpaul Bit Poster

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    thanks for the input r.h.lee, but can i save you the bother of writing a series of one-sentence posts by letting you know that i have been helped already?
    Ta anyway.
     
    Certifications: Nothing spoddy,all electrickery so far
    WIP: a+

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