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7675 Views 26 Replies Latest reply: Mar 14, 2014 10:47 PM by Ankur RSS 1 2 Previous Next

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route summarization

Sep 27, 2012 5:32 AM

florian 248 posts since
Oct 8, 2010



one question regading route summarization.


how would you summarize the routes:


thought it would be, but according to my book thats wrong and i dont understand why.


thanks for any help!

  • Currently Being Moderated
    1. Sep 27, 2012 6:02 AM (in response to florian)
    Re: route summarization

    It will also be my guess. is it the OCG route book?

  • Currently Being Moderated
    2. Sep 27, 2012 6:07 AM (in response to Anders Jul)
    Re: route summarization



    It should be



  • ESummers 312 posts since
    Sep 10, 2010
    Currently Being Moderated
    3. Sep 27, 2012 6:27 AM (in response to florian)
    Re: route summarization would also include network, which may or may not be a good thing depending on the design.


    You may need to advertise:

  • Donnie 38 posts since
    Mar 30, 2012
    Currently Being Moderated
    4. Sep 27, 2012 6:32 AM (in response to florian)
    Re: route summarization

    Good question,

    I'm afraid if I answer it I may be wrong, so I will simply say that I have gotten it right on certifications, but gotten it wrong in class tons of times. Can anyone document the stupid-proof steps to ensure that I never confuse it again?

  • Currently Being Moderated
    6. Sep 27, 2012 7:10 AM (in response to florian)
    Re: route summarization

    it's because the the mask is /22 = in binary 1octet.2octet.11111100.00000000


    WIth the last to bits you get 4 combinations







    in numbers this will result:







    So subnets will look lige


    and so on...

  • Currently Being Moderated
    7. Sep 27, 2012 7:16 AM (in response to Anders Jul)
    Re: route summarization



    The third octet for the IP addresses is

  --- 0000 0001 --- 0000 0010 --- 0000 0011


    if you want to have one summary address for all three the common bits are the first six and the last two varies. So you will put the last two as a host bit which will make the subnet mask /22. subnet mask 22 means the last 10 bit of the 32 bit IP address will be the host bits and the first 22 as a network bits. and when you indicate the network you will always use 0 on the host portion so the last 10 bits will be 0 for the summary network address. and since the first six bits of the third octet are common 0000 00 and the last two will be used as a host bits which will be 00 will make the third octet 0000 0000.


    so the summary address will be



  • sambotech12 727 posts since
    Apr 3, 2012
    Currently Being Moderated
    8. Sep 27, 2012 11:22 AM (in response to florian)
    Re: route summarization

    florian wrote:


    hi all,


    thanks for the fast replies.


    no its actually not the OCG, but a ccna book from mcgraw hill.


    iam confused cause there are multiple examples like the one mentioned above, but with a different outcome.



    the summary route would be:

    i understand this cause the first 22 network bits match, thus this is the mask and the is the smallest ip address from all of them.


    but the example with the networks i dont understand. could someone please clarify why it is and not


    i understand how to come up with the netmask, but why is it and not




    Hey florian,


    You should change the addresses into their binary form.  It will be clear as day then.  The summary address doesn't use the smallest IP address.  It uses the common bits of the addresses you are trying to summarize starting from the left side.






  • Uttam 362 posts since
    Mar 27, 2011
    Currently Being Moderated
    9. Sep 27, 2012 11:47 AM (in response to sambotech12)
    Re: route summarization



    would you like to share that excel file



  • sambotech12 727 posts since
    Apr 3, 2012
    Currently Being Moderated
    10. Sep 27, 2012 12:28 PM (in response to Uttam)
    Re: route summarization

    Uttam wrote:




    would you like to share that excel file



    Hi Uttam,


    ICND1, ICND2, and CCNA students really need to learn and practice these concepts until they can pretty much do them in their heads to pass the tests.  If they let MS Excel do the work for them, they most likely will not pass.  So do you want the Excel file to check your work?  I can see the point in sharing the file as a learning tool.



  • sambotech12 727 posts since
    Apr 3, 2012
    Currently Being Moderated
    11. Sep 27, 2012 5:25 PM (in response to Uttam)
    Re: route summarization

    Hey Uttam,


    You never answered my question.  I just don't want ICND1, ICND2, and CCNA students using these files instead of practicing on their own.  If they fail their exams they're going to blame me.  A kind of "I provided the poisonous apple that they took a bite out of" situation.


    Anyway......I have three MS Excel files.  The first one is a 'Subnet' file.  The user enters an IP address and prefix length in the top row and the file will break it down into the following:


    1. Host Address (binary)
    2. network / host components
    3. Subnet Mask (binary)
    4. Network Address (binary)
    5. Network Address (decimal)
    6. First Usable Address (decimal)
    7. Last Usable Address (decimal)
    8. Broadcast Address (binary)
    9. Broadcast Address (decimal)
    10. Class A, B, or C with significant bits indicator
    11. Magic Number
    12. Interesting Octet
    13. Octet Indicator
    14. A list of the subnets
    15. A button to locate the subnet of the host address among the list of subnets


    The following two pictures are snapshots of the file:






    The second file is a 'Summarization' file.  As you can probably guess the file is for summarizing routes.  The user enters a route in the top row in the form of an IP address and prefix length and pushes the 'Summarize' button.  The program will compute the summary address with any previously entered routes.  So the user enters a route and pushes the button....enters another route and pushes the button....and so on.  A picture of the file is below.






    And the last file is a 'VLSM / SLSM Calculator'.  The user enters an address block in the form of a network IP address and prefix length in the top row.  The user also has to enter on the left-hand side the names and sizes of the subnets.  The subnets do not have to be in any particular order.  The program will list them from largest to smallest subnets.  Do not include the network and broadcast addresses in the size for each subnet....the algorithm already accounts for that.  So, for example, a /28 will accomodate up to a size of 14.  A size of 15 or 16 will require a /27.  If the entered address block is actually a host address, when the user pushes the 'Submit' button he/she gets a warning and the program stops.  There is also a visual indicator for a valid/invalid subnetting scheme.  A subnetting scheme is invalid if the total number of hosts goes beyond the address block.  The calculator stops subnetting once the addresses of the address block are all used up.


    I also have to explain the 'RESET' button.  To the right of the reset button is a number.  It's highlighted in green.  That number designates which part of the table is erased or reset.  It works as follows:


    • a '0' deletes the addresses in the yellow/green colored areas when the 'RESET' button is pushed
    • a '1' deletes the subnet sizes when the 'RESET' button is pushed
    • a '2' deletes the subnet names when the 'RESET' button is pushed


    The number cycles as the 'RESET' button is pushed.  It goes from 0, to 1, to 2, to 0, to 1, and so on.  The number can also be changed manually.  So the user has some control of what he/she wants to delete from the table.




    A picture of an invalid host address block:






    A picture of an invalid subnetting scheme:






    A picture of a valid subnetting scheme:






    Those are my Excel files.  Since you, Uttam, are the only person who has ever asked me for my Excel files, I'll leave the decision up to you.  If you think it's a good idea to give ICND1, ICND2, and CCNA students access to these files, I'll upload the files to the 'Documents' directory of my profile so that anyone could download them.  If you think they will use them in a positive way, as learning tools, I don't mind sharing.  If they fail the exams due to a lack of subnetting practice, the blame is on you....not me.  So what do you think?



  • Jeff 65 posts since
    Dec 4, 2010
    Currently Being Moderated
    13. Sep 28, 2012 12:31 AM (in response to Age)
    Re: route summarization

    Lets see an example here

    With a typical network "" , you wouldnt say it as ""or"" network , right?

    Since is one of the ip address included within "" network,you cant reference it as"" network.

  • Currently Being Moderated
    14. Sep 28, 2012 5:23 AM (in response to florian)
    Re: route summarization

    That is right...




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