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  • Subnetting

    Hi,

    Maybe not a bright question but forgive me my ignorance.

    Let's say I wanted to subnet a class B address with subnet 255.255.254.0

    so i know i have 126 subnets

    510 hosts per subnet

    Now here is my question

    When i start the first host 2.1 to the last 3.254 that is one subnet


    Then I start 4.1 to 5.254 the second one


    Now between these subnets do I just use a switch? or a router? Or you just use a router when ur subnet is completely different? Let's say if I had a 255.255.240 address?

  • #2
    Re: Subnetting

    You'll need to use a router.
    Originally posted by Daveinholland View Post
    Let's say I wanted to subnet a class B address with subnet 255.255.254.0
    I think some of your confusion is that 255.255.254.0 is a subnet mask. A subnet mask lets you know, among other things, how big your subnet is.

    Here's a good article about IP addressing http://www.3com.com/other/pdfs/infra..._US/501302.pdf

    Thanks for the post.
    Let us know if you have anymore questions.
    Regards,
    Jeremy

    Network Consultant/Engineer
    Baltimore - Washington area and beyond
    www.gma-cpa.com

    Comment


    • #3
      Re: Subnetting

      Ah thx a lot.

      I was wondering do you also know a great article about vlsm?

      Comment


      • #4
        Re: Subnetting

        Have you looked at the link? It has 13 pages dealing specifically with VLSM (starting on page 21) and it's followed by a CIDR section which is closely related to VLSM. If those 13 pages are not enough then I would search the web for articles or find a good book on the subject.
        Regards,
        Jeremy

        Network Consultant/Engineer
        Baltimore - Washington area and beyond
        www.gma-cpa.com

        Comment


        • #5
          Re: Subnetting

          Originally posted by Daveinholland View Post
          Hi,

          Maybe not a bright question but forgive me my ignorance.

          Let's say I wanted to subnet a class B address with subnet 255.255.254.0

          so i know i have 126 subnets

          510 hosts per subnet

          Now here is my question

          When i start the first host 2.1 to the last 3.254 that is one subnet


          Then I start 4.1 to 5.254 the second one


          Now between these subnets do I just use a switch? or a router? Or you just use a router when ur subnet is completely different? Let's say if I had a 255.255.240 address?
          OK.... let's say your original Class B address is 160.160.0.0 (A0 A0 00 00 hex) your subnet mask of FF FF FE 00 means that basically anything from A0 A0 00 00 to A0 A0 FE 00 (with an EVEN third octet) is one of "your" subnets.

          A router will be required for any of these subnets to talk to any other subnet and/or any other network such as the Internet. Let's say for instance that you decide to use only two of your networks:

          A0 A0 02 00 (160.160.2.0) and A0 A0 FE 00 (160.160.254.0) you can see that they're STILL separate networks, because the subnet mask has masked off all the bits we're using, so that we can identify the network ID.

          What about all the ODD octets, I hear you cry? Well - because your subnet mask stops at bit one of the third octet, and leaves bit zero as a zero, then the "1" at the end that would make it odd is part of the host ID, NOT the network ID.

          So for instance, host 160.160.255.0 is host number 256 on the 160.160.254.0 network... (NOTE - before anyone says ANYTHING - the Host ID is NOT all zeroes in this case; it has a "1" in the bit 8 position...)

          255 255 254 0
          1111 1111 * 1111 1111 * 1111 1110 * 0000 0000

          1010 0000 * 1010 0000 * 1111 1110 * 0000 0000 = Network ID - 160.160.254.0

          * * 1 * 0000 0000 = Host ID ..1.0
          Last edited by Stonelaughter; 18th December 2006, 23:36. Reason: minor error in the numbers


          Tom
          For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

          Anything you say will be misquoted and used against you

          Comment


          • #6
            Re: Subnetting

            Hi Daveinholland,

            Just to answer the question at the end of your original post-

            If you want two subnets to communicate you must have a router between the subnets to route. Say you had two subnets that you wanted to connect. The router would have two interfaces - one to each subnet.

            If you put a switch in between subnets, they would be physically connected but would not be able to communicate.

            That was a good question.

            If you have more questions, please post em' here.

            Thanks,
            David
            David Davis - Petri Forums Moderator & Video Training Author
            Train Signal - The Global Leader in IT Video Training
            TrainSignalTraining.com - Free IT Training Products
            Personal Websites: HappyRouter.com & VMwareVideos.com

            Comment


            • #7
              Re: Subnetting

              Originally posted by daviddavis View Post
              Hi Daveinholland,

              Just to answer the question at the end of your original post-
              Originally posted by stonelaughter
              A router will be required for any of these subnets to talk to any other subnet and/or any other network such as the Internet.
              ??!?!!!?!??


              Tom
              For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

              Anything you say will be misquoted and used against you

              Comment


              • #8
                Re: Subnetting

                Tom,
                Please accept my apologies!
                You did an excellent job answering this question and I didn't read thoroughly before responding to see that you had already answered it, and had gone above and beyond.
                I am going to give you reputation points because I appreciate your posting so much!
                Again, sorry about that.
                David
                David Davis - Petri Forums Moderator & Video Training Author
                Train Signal - The Global Leader in IT Video Training
                TrainSignalTraining.com - Free IT Training Products
                Personal Websites: HappyRouter.com & VMwareVideos.com

                Comment


                • #9
                  Re: Subnetting

                  Thank you - and no apology needed - I guess I could have bolded it or something as the actual answer to his actual question!


                  Tom
                  For my own and your protection, I do not provide support by private message under any circumstances. All such messages will be deleted and ignored.

                  Anything you say will be misquoted and used against you

                  Comment


                  • #10
                    Re: Subnetting

                    Originally posted by JeremyW View Post
                    You'll need to use a router.
                    Sould I jump on the band wagon?
                    Regards,
                    Jeremy

                    Network Consultant/Engineer
                    Baltimore - Washington area and beyond
                    www.gma-cpa.com

                    Comment


                    • #11
                      Re: Subnetting

                      ...or a layer 3 switch?? i.e Cisco 3750.
                      Thank you,

                      Marc

                      Comment

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