7 Replies Latest reply: Dec 18, 2010 3:45 AM by Zaher Hamiyah RSS

    question about subneting

    student

      Hello Guys,

       

      I have some questions about subneting, I have attached the file in this discussion which has the question.

       

      I hope my question is clear.

       

       

      Message was edited to remove exam details by:

      Rigo

      Cisco Learning Network Moderator

        • 1. Re: question about subneting
          cjinfantino

          Hey,

           

          Looking at the diagram, the network address under 'Admin' was blurred out. So assuming that is 172.16.3.96 then yes "C" would be a good answer for Network A.

           

          For Link A I would choose answer "D" and the reason is what they are really asking is to assign addresses to Link A and Network A that will not overlap with other networks (because each router interface is a network boundary). It is also assumed they would want to have the most efficient use of the address space.

           

          Answer "D" will use the address 0-3 that is currently not being used. Also because it is a link, you will only need two addresses for each interface on the router. A /30 network does just that, 0 will be the network address, .3 is the broadcast address, .1 and .2 will be the addresses for your router interfaces.

           

          Hope that helps!

          • 2. Re: question about subneting
            student

            Hi Cjin

            Thanks for your reply, I understand what you mean, yes you are right, the 2nd choice of correct answer is "D"  but why "D"? Why not "E"? Even the IP address shown in answer "E" has 30 bits of Subneting "/30".

             

            I hope you understand what I mean,

             

            • 3. Re: question about subneting
              DelVonte

              If  the Admin VLAN is 172.16.3.96 /27, then using E for Link A would overlap with this subnet. In order to prevent any overlapping subnets, D is the best answer for Link A.

               

              HTH

              DelVonte

              • 4. Re: question about subneting
                Martin

                C and D are 2 answers. For 120 hosts, you need 7 bits; that leaves 1 bit for subnet, which is /25.

                • 5. Re: question about subneting
                  student

                  Hi Guys,

                   

                  DelVonte,thanks for your reply, but this question is not actually about VLANs and

                  in the diagram ,their is no switch and VLANs are created in switches. My question

                  was that why do we choose the answer D for Link A ?Why not the answer "E" for link A becoz even the ip address in answer "E" has 30 bits subneting "30/"?

                   

                  I hope now my question is more clear.

                  • 6. Re: question about subneting
                    Andreas Thrasivoulou

                    For Link A the correct answer is D because is a point to point which you only need 2 IPs usable the /30 link. you dont use E because that IPs can be used in a larger subnet. to better understand break the network in smaller pieces starting from the end.

                     

                    You have 172.16.3.0/24 break these network into to /25 networks 172.16.3.0/25 and 172.16.3.128/25 (these will be used for Network A so is gone)

                     

                    then break the 172.16.3.0/25 into smaller and these i believe will help you understand the subnetting

                    • 7. Re: question about subneting
                      Zaher Hamiyah

                      Student,

                       

                      you are posting illegal materials which is totally prohibited.