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  1. Junior Member
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    #1

    Default Summarizing a block of IP addresses

    How would you go about summarizing the following contiguous block of subnets:

    10.48.226.x /25
    10.48.227.x /25

    all the way through to

    10.48.252.x /25


    I have the answer as 10.48.224.0 /19, however I am not sure why/how this is.

    Any advice would be appreciated.
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  3. chX
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    #2
    I'd first convert the IP addresses to binary:

    10.48.226.x
    10.48.227.x
    ...
    10.48.252.x
    ___________________________

    00001010.00110000.11100010.x
    00001010.00110000.11100011.x
    ...
    00001010.00110000.11111100.x


    Now compare which bits are similar across all of the addresses (red).

    00001010.00110000.11100000.x

    Convert it back to decimal:

    10.48.224.x

    Count the number of bits up until the point they do not all match (the three red bits)

    19.

    10.48.224.x /19


    Hope that makes sense!
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  4. Senior Member chmorin's Avatar
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    #3
    chX is on the money. That's how you do it.
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  5. Junior Member
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    #4
    Quote Originally Posted by chX View Post
    I'd first convert the IP addresses to binary:

    10.48.226.x
    10.48.227.x
    ...
    10.48.252.x
    ___________________________

    00001010.00110000.11100010.x
    00001010.00110000.11100011.x
    ...
    00001010.00110000.11111100.x


    Now compare which bits are similar across all of the addresses (red).

    00001010.00110000.11100000.x

    Convert it back to decimal:

    10.48.224.x

    Count the number of bits up until the point they do not all match (the three red bits)

    19.

    10.48.224.x /19


    Hope that makes sense!

    cheers, just what I was looking for, a simple explanation.

    It seems so straightforward now!
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  6. Junior Member Registered Member
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    #5

    Default summarization dielema

    heyy, i would be really glad if u help me out.
    i was studying summarization from todd lammle ccna guide, and one thing was confusing me was this:- summarization of 192.168.144.0/20.
    how r we using /20 as a mask in a class c network. doesnt it strts from /24 through /30????
    plzz help me out. i m totally confused.
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  7. Senior Member
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    #6
    Quote Originally Posted by palsantanu71 View Post
    heyy, i would be really glad if u help me out.
    i was studying summarization from todd lammle ccna guide, and one thing was confusing me was this:- summarization of 192.168.144.0/20.
    how r we using /20 as a mask in a class c network. doesnt it strts from /24 through /30????
    plzz help me out. i m totally confused.
    Why could you not use a /20 subnet? By default a Class C network has a /24 subnetmask. If you use /24, you subnetting a Class C network into smaller parts. Using /20 is going the otherway around, making it bigger.
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