1 2 Previous Next 28 Replies Latest reply: Aug 3, 2014 10:31 PM by Darren Starr (CCSI, 4xCCNP, 7xCCNA) RSS

    route summarization

    florian

      hi,

       

      one question regading route summarization.

       

      how would you summarize the routes:

       

      10.1.1.0/24

      10.1.2.0/24

      10.1.3.0/24

       

      thought it would be 10.1.1.0/22, but according to my book thats wrong and i dont understand why.

       

      thanks for any help!

        • 1. Re: route summarization
          Anders Jul Jensen

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

          • 2. Re: route summarization
            Age

            Hi,

             

            It should be 10.1.0.0/22.

             

            Thanks

            • 3. Re: route summarization
              ESummers

              10.1.0.0/22 would also include network 10.1.0.0, which may or may not be a good thing depending on the design.

               

              You may need to advertise:

              10.1.1.0/24

              10.1.2.0/23

              • 4. Re: route summarization
                Donnie

                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?

                • 5. Re: route summarization
                  florian

                  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.

                  e.g.

                  192.168.0.0/24

                  192.168.1.0/24

                  192.168.2.0/24

                  192.168.3.0/24

                   

                  the summary route would be: 192.168.0.0/22

                  i understand this cause the first 22 network bits match, thus this is the mask and the 192.168.0.0 is the smallest ip address from all of them.

                   

                  but the example with the 10.1.1.0 networks i dont understand. could someone please clarify why it is 10.1.0.0/22 and not 10.1.1.0/22.

                   

                  i understand how to come up with the netmask, but why is it 10.1.0.0 and not 10.1.1.0

                   

                  thanks.

                  • 6. Re: route summarization
                    Anders Jul Jensen

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

                     

                    WIth the last to bits you get 4 combinations

                     

                    00

                    01

                    10

                    11

                     

                    in numbers this will result:

                     

                    0

                    1

                    2

                    3

                     

                    So subnets will look lige

                     

                    10.1.0.0

                    10.1.4.0

                    10.1.8.0

                    10.1.12.0

                    and so on...

                    • 7. Re: route summarization
                      Age

                      Right...

                       

                      The third octet for the IP addresses is

                       

                      10.1.1.0/24 --- 0000 0001

                      10.1.2.0/24 --- 0000 0010

                      10.1.3.0/24 --- 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 10.1.0.0/22.

                       

                      Thanks,

                      • 8. Re: route summarization
                        sambotech12

                        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.

                        e.g.

                        192.168.0.0/24

                        192.168.1.0/24

                        192.168.2.0/24

                        192.168.3.0/24

                         

                        the summary route would be: 192.168.0.0/22

                        i understand this cause the first 22 network bits match, thus this is the mask and the 192.168.0.0 is the smallest ip address from all of them.

                         

                        but the example with the 10.1.1.0 networks i dont understand. could someone please clarify why it is 10.1.0.0/22 and not 10.1.1.0/22.

                         

                        i understand how to come up with the netmask, but why is it 10.1.0.0 and not 10.1.1.0

                         

                        thanks.

                         

                        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.

                         

                        Summary_2.jpg

                         

                        Hth,

                        -sambotech12

                        • 9. Re: route summarization
                          Uttam

                          Sambotech,

                           

                          would you like to share that excel file

                           

                           

                           

                          • 10. Re: route summarization
                            sambotech12

                            Uttam wrote:

                             

                            Sambotech,

                             

                            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

                            • 11. Re: route summarization
                              sambotech12

                              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:

                              Subnet_1.jpg

                               

                              Subnet_2.jpg

                              =================================================================

                               

                              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.

                               

                              Summary_2.jpg

                               

                              =====================================================================

                               

                              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:

                               

                              VLSM_Inv_blk.jpg

                               

                              ====================================

                               

                              A picture of an invalid subnetting scheme:

                               

                              VLSM_Inv_sub.jpg

                               

                              ===================================

                               

                              A picture of a valid subnetting scheme:

                               

                              VLSM_Val_sub.jpg

                               

                              =================================

                               

                              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?

                               

                              -sambotech12

                              • 12. Re: route summarization
                                florian

                                so i actually just say that the host bits are always 0 for this matter? and i just use the network bits for the summary network?

                                 

                                e.g.

                                192.168.1.0/24

                                192.168.2.0/24

                                192.168.3.0/24

                                 

                                the first 2 octects are the same and the 3rd:

                                 

                                00000001

                                00000010

                                00000011

                                 

                                so subnet mask would be /22 and the summary address 192.168.0.0. cause the last two bits are host bits and i just set them to 0 to find the summary address. right?

                                 

                                thanks!

                                • 13. Re: route summarization
                                  Jeff

                                  Lets see an example here

                                  With a typical network "192.168.1.0/24" , you wouldnt say it as "192.168.1.1/24"or"192.168.1.2/24" network , right?

                                  Since 10.1.1.0 is one of the ip address included within "10.1.0.0/22" network,you cant reference it as"10.1.1.0/22" network.

                                  • 14. Re: route summarization
                                    Age

                                    That is right...

                                     

                                    Thanks

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