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  1. Junior Member Registered Member
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    #1

    Default Summarizing an address

    Can someone please help me with this:
    Summarize the following without over-summarizing:
    10.22.0.0/23
    10.22.4.0/23
    10.22.2.0/24
    10.22.3.0/24
    10.22.7.0/24
    And how will the summarized address look if I add 10.22.6.0/24?

    My answer would be 10.22.0.0/21 and the summarized address won't change if we add 10.22.6.0/24.

    Also I would like to know what is the difference between not over-summarizing and over-summarizing with these same addresses.
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    #2
    Your answer is correct and nothing changes if you add that address.

    10.22.0.0/21 covers 10.22.0.0-10.22.7.255

    If you did 10.22.0.0/20, you would be over-summarizing because you are covering subnets that are not being asked to be summarized. It doesn't really apply here, but if you pretend that you were looking to include 10.22.8.0/24 and 10.22.9.0/24, using 10.22.0.0/20 would be over-summarizing because the summary includes additional address blocks that you are not necessarily trying to advertise in the summary address. To do it properly, you may consider two summary addresses; 10.22.0.0/21 and 10.22.8.0/23. You can go with 10.22.0.0/20 in that hypothetical example I provided potentially, but I would recommend going with the two separate summaries. Hope that helps.
    Last edited by hurricane1091; 01-23-2017 at 01:19 PM.
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  4. Junior Member Registered Member
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    #3
    If I want to be sure to not over-summarize can I make 2 summarized addresses, 10.22.0.0/22 and 10.22.4.0/22, where 10.22.4.0/22 would also include the added 10.22.6.0 address?
    Also, thank you very much for answering.
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  5. There is no spoon. p@r0tuXus's Avatar
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    #4
    For address summarization, whether for your ACLs or your Route Statements, the VLSM for CCNA level studies will probably require one address, not two, and this is just to ensure you know how to summarize. It's probably best not to over-complicate the CCNA as it's all ready a lot to wrap your head around.

    For the listed addresses above, you would summarize the largest necessary address and mask and no more. 10.22.0.0 /21

    Address / Mask- Binary Address (Network/Host Bits)
    10.22.0.0/23 00001010.00010110.00000000.00000000
    10.22.2.0/24 00001010.00010110.00000010.00000000
    10.22.3.0/24 00001010.00010110.00000011.00000000
    10.22.4.0/23 00001010.00010110.00000100.00000000
    10.22.6.0/24 00001010.00010110.00000110.00000000
    10.22.7.0/24 00001010.00010110.00000111.00000000
    10.22.0.0/21 00001010.00010110.00000111.00000000

    The last octet is fairly irrelevant, the largest host bit number in the 3rd octet becomes the most relevant as you'll have to have enough network bits to accomodate in the subnet mask to encompass all the ranges. Hence: 10.22.0.0 /21 would work fine.
    Last edited by p@r0tuXus; 01-23-2017 at 11:01 PM.
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