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  • Vlsm

    Hey, I'm currently trying to create a subnetted network using 172.16.0.0 for internal addressing. The deal is i need 1262 hosts and don't want to waste addresses. How would I use VLSM to conquer this problem? I understand VLSM is subnetting a subnet, but I just have a hard time with that concept. Thanks

  • #2
    Re: Vlsm

    http://www.subnet-calculator.com/cidr.php

    Maybe

    172.16.0.0/21 which gives 172.16.0.0 - 172.16.7.255
    cheers
    Andy

    Please read this before you post:


    Quis custodiet ipsos custodes?

    Comment


    • #3
      Re: Vlsm

      So basically I'd have 8 subnets with 256 possible hosts -2 after network and broadcast addresses. My effective range would be 172.16.0.1-172.16.0.254 and so on?

      Would any of these be wasted? Further more How Do I subnet a subnet? And Could I Put a /8 CIDR mask on a 172.16.0.0 network without wasting addresses?

      Comment


      • #4
        Re: Vlsm

        What do you mean by wasted? You can't have "completely" free reign with the amount of hosts due to the multiples involved so you usually have to accept the next highest number to get your range.

        Your range is 172.16.0.0 - 172.16.7.255

        Note the 7 in the 3rd octet.

        Subnet a subnet?
        Well 172.16.0.0 255.255.255.0 (or 172.16.0.0 /24)
        is 172.16.0.0 - 172.16.0.255

        therefore to subnet that you could have

        172.16.0.0 255.255.255.224
        which is
        172.16.0.0 to 172.16.0.31
        then
        172.16.0.32 to 172.16.0.63
        and so on.

        You could then setup a machine with an IP address of 172.16.0.3 255.255.255.224 which can only ping machines that fit within its subnet of 172.16.0.0 to 172.16.0.31
        Attached Files
        cheers
        Andy

        Please read this before you post:


        Quis custodiet ipsos custodes?

        Comment


        • #5
          Re: Vlsm

          Well the 1,362 devices are split into a 750 lan and and a 512, so you see I have to use an appropriate size for both, and also include 3 wan networks that i've already deduced have a mask of /30.

          /22 gives me 1022 possible hosts for my network with 750

          but I have a network with exactly 512 devices that need addressing.

          Would I simply be putting both on the same network and then utilize a /21?

          Comment


          • #6
            Re: Vlsm

            http://www.microsoft.com/technet/pro....mspx?mfr=true

            It's been such a long time since I thought about this....

            So you want separate networks a 750 and a 512? When you stated you needed 1262 (or 1362) hosts I thought that was as one network.

            The 512 will need the next bigger size as you lose the 2 as you suggest. This is a common thing to catch people out. This means you can treat the 750 and 512 as the same size pretty much.

            172.16.0.0 - 172.16.3.255 for the 750 (total 1022 hosts allowed)
            172.16.4.0 - 172.16.7.255 for the 512 (total 1022 hosts allowed)

            note they are the same as we can't drop the 512 to a smaller one because of the -2 for network and broadcast.

            which gives 172.16.0.0 - 172.16.7.255
            or 172.16.0.0 255.255.248.0
            or 172.16.0.0 /21

            Your router needs to talk to both but I am assuming your networks should only talk through the router? If so then the router would need something like
            172.16.0.0 0.0.7.255 I would guess
            cheers
            Andy

            Please read this before you post:


            Quis custodiet ipsos custodes?

            Comment


            • #7
              Re: Vlsm

              Well the idea is the have all serial interfaces on /30, and the other networks on a different subnet masking scheme. You waste addresses if you don't have each network on a different masking scheme.

              Comment


              • #8
                Re: Vlsm

                /30 is only 2 addresses usable (I do realise you know) which will be the routers interface at either end and they only need to talk to each other so this is fine. Whereabouts are these different networks with the 750 and 512 ranges?

                Is there a specific question you have been asked that is a bit broader than the original post?
                cheers
                Andy

                Please read this before you post:


                Quis custodiet ipsos custodes?

                Comment


                • #9
                  Re: Vlsm

                  Here's a suugestion for your router interfaces:

                  Don't create subnets or use addresses for the serial interfaces from your 172.16.0.0 network address so that you don't create wasted subnets or addresses. Since the serial interfaces only need to communicate with each other use a different RFC 1918 address range such as 10.0.0.0. For instance use 10.0.0.1/8 on one router serial interface and 10.0.0.2/8 on the other router serial interface.

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