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Example Microsoft Subnet Question

Discussion in 'Networks' started by miff2009, May 14, 2009.

  1. miff2009

    miff2009 New Member

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    Hi All,

    I've been reading up on Subnetting and applied what I learnt to the following Microsoft exam example but I don't know how they derived the Network Addresses, may be someone can offer a better explanation. Thanks.


    Question:

    Your boss asked you to subnet a network in the lab for an upcoming class. He hands you a piece of paper while he's on the phone and it simply says "192.168.10.x/25. 4 subnets." What is the subnet mask and the first address in each subnet?


    Correct Answer:

    255.255.255.128 / 192.168.10.1, 192.168.10.33, 192.168.10.65, 192.168.10.97

    (I got the answer right, based on the subnet - as it was the only one that had 128 in the answer, however, I didn't get the Network Addresses correct)



    Explanation given:

    Using the network notation /25 indicates you need to use 25 network bits. 255.255.255.0 typically is used for the default subnet mask for Class C networks and uses 24 bits (often noted /24). Therefore, if you add one bit, you change the left-most bit in the right-most octet to 1. This equals 128, creating a subnet mask of 255.255.255.128. The starting addresses (the first assignable IP address) in each subnet would have the right-most octet set to 1, 33, 65, and 97. The network addresses themselves would be 192.168.10.0, 192.168.10.32, 192.168.10.64, and 192.168.10.96.




    I don't understand how they derived the number of Hosts, and it's making the assumption that the first network is 192.168.10.0.

    I read the following site on Subnetting and used the same principles but didn't get it right. http://www.pantz.org/software/tcpip/subnetchart.html
     
  2. danielno8

    danielno8 Gigabyte Poster

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    that subnet mask with 192.168.10.0 gives you:

    192.168.10.0-->127 (host range 1-126)
    192.168.10.128-->255 (host range 129-254)

    To get the First host addresses given as the correct answer you would need a subnet mask of /27 or 255.255.255.224 not /25
     
    Certifications: CCENT, CCNA
    WIP: CCNP

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