6 Replies Latest reply: Nov 23, 2018 7:36 AM by mike RSS

    Lab subnetting question

    mike

      So I am trying to separate my lab network from my home network.  I have a physical firewall (ipcop) that I created a new segment on.

      I configured that segment as 10.1.2.0 /23, making the interface 10.1.2.1 /23

       

      my question is how do I subnet that on the router?  My first thought was just to set g0/0 to 10.1.2.2 /23, then create subinterfaces g0/1.xx with all my subnets.

      but of course I get the ip overlaps with g0/0 error

       

      Any help would be appreciated.

         
        • 1. Re: Lab subnetting question
          Ing_Percy

          Hi!

           

          If you want to creat subnets, you must vary the subnets mask (VLSM), for example

           

          your network base: 10.1.2.0/23

          Range: from 10.1.2.0 to 10.1.3.255

           

          *You could form the following subnets:

          10.1.2.0/24

          10.1.3.0(24

           

          **Another alternative to form subnets:

          10.1.2.0/25

          10.1.2.128/25

          10.1.3.0/25

          10.1.3.128/25

           

          The configuration will be the following (**)

           

          interface g0/1

           

          interface g0/1.10

          encapsulation dot1q 10

          ip add 10.1.2.1 255.255.255.128

           

          interface g0/1.20

          encapsulation dot1q 20

          ip add 10.1.2.129 255.255.255.128

           

          interface g0/1.30

          encapsulation dot1q 30

          ip add 10.1.3.1 255.255.255.128

           

          interface g0/1.40

          encapsulation dot1q 40

          ip add 10.1.3.129 255.255.255.128

           

          Best regards!

          • 2. Re: Lab subnetting question
            mike

            Exactly, however

             

            int g0/0

            ip add 10.1.2.2 255.255.254.0    << This goes to my firewall (10.1.2.1 /23)

             

            int g0/1.10

            encap dot1q 10

            ip add 10.1.3.1 255.255.255.0

             

            % 10.1.3.0 overlaps with g0/0    <<<  Just get the overlap error, and of course it does overlap.

            • 3. Re: Lab subnetting question
              Ing_Percy

              Hi!

               

              You are producing "overlapping"

               

              10.1.2.2 255.255.254.0

              The network ID is 10.1.2.0/23, the range is:from 10.1.2.0 to 10.1.3.255


              For that reason, when you configure the ip add 10.1.3.1 255,255,255,0, it has already been used by the another interface.

               

              You must apply subnet from the initial fase.

               

              Now if you have currently connections, then, you could consider modify the subnet mask of another devices.

              Is your network in production? or is it a lab of your course?

               

              Best regards!

              • 4. Re: Lab subnetting question
                mike

                Yes, i am overlapping.

                This is just a lab, so i can easily recreate anything

                 

                What I am trying to accomplish is subnetting the /23 into many smaller subnets within the lab.

                Just not sure how to do that initial break down.  I have the /23 on g0/0 where do I go from there?

                • 5. Re: Lab subnetting question
                  Ing_Percy

                  Hi!

                   

                  As I mentioned in my first post, you must apply subnets

                   

                  When you configure subinterface, it is a good practice not configure the physical interface. Only you configure the subinterfaces and associate these subinterfaces with a corresponding vlan (with the command: "encapsulation")

                   

                  For example

                   

                  interface g0/1

                   

                  interface g0/1.10

                  encapsulation dot1q 10

                  ip add 10.1.2.1 255.255.255.128   ---- VLAN 10, you could consider this subnet to connect your firewall

                   

                  interface g0/1.20

                  encapsulation dot1q 20

                  ip add 10.1.2.129 255.255.255.128

                   

                  interface g0/1.30

                  encapsulation dot1q 30

                  ip add 10.1.3.1 255.255.255.128

                   

                  interface g0/1.40

                  encapsulation dot1q 40

                  ip add 10.1.3.129 255.255.255.128

                   

                  Best regards!

                  • 6. Re: Lab subnetting question
                    mike

                    Got it.  And it works!

                    I never would have tried to connect a non trunk connection that way.

                     

                    Thanks!