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    DHCP Question...

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    wrcombs dhcp networking
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    • KellyK
      Kelly @JaredBusch
      last edited by

      @JaredBusch said in DHCP Question...:

      The DHCP range is always the full subnet. That is standard, even if Windows lets you do stupid shit.

      Here is my home router.
      Instead of visibly showing ranges to exclude, outside of windows, you typically tell it hat range to pass out. I'm passing out .31 - .254
      Primary DNS is my PiHole on .4
      Secondary DNS is the router on .1

      ef0668bf-f775-4b9d-af0e-3fa87b13a940-image.png

      Can you clarify something for me @JaredBusch. You stated that DHCP range is always the full subnet, but yours is from .31 to .254. I feel like I'm missing something.

      JaredBuschJ 1 Reply Last reply Reply Quote 1
      • JaredBuschJ
        JaredBusch @Kelly
        last edited by

        @Kelly said in DHCP Question...:

        @JaredBusch said in DHCP Question...:

        The DHCP range is always the full subnet. That is standard, even if Windows lets you do stupid shit.

        Here is my home router.
        Instead of visibly showing ranges to exclude, outside of windows, you typically tell it hat range to pass out. I'm passing out .31 - .254
        Primary DNS is my PiHole on .4
        Secondary DNS is the router on .1

        ef0668bf-f775-4b9d-af0e-3fa87b13a940-image.png

        Can you clarify something for me @JaredBusch. You stated that DHCP range is always the full subnet, but yours is from .31 to .254. I feel like I'm missing something.

        DHCP always serves the entire subnet it is defined on.

        If you tell it the scope is a /24, it serves .1-.254 always.
        You then subsequently define which part of the scope you want it to hand addresses out on.

        In windows that is done by "excluding" things.
        On most other platforms, it is done by telling it what range to supply to clients that ask for an address. Hence the .31 through .254

        But regardless of what you specify, either as a range to use or range to exclude, DHCP still serves the entire scope.

        This is why you can make reservations outside of the listed range as in my .7 printer and .10 phone.

        PhlipElderP 1 Reply Last reply Reply Quote 1
        • JaredBuschJ
          JaredBusch
          last edited by

          Here is a shot from Windows Server 2012 R2.

          I have had to explain many times over the years that just because you "exlcude" a range, it does not mean you cannot put a DHCP reservation in that excluded range. Because DHCP is still and always serving the entire subnet defined in the scope.
          42e53403-2096-44be-8f38-4b11d0fa68cb-image.png

          DashrenderD 1 Reply Last reply Reply Quote 0
          • PhlipElderP
            PhlipElder @JaredBusch
            last edited by PhlipElder

            @JaredBusch said in DHCP Question...:

            @Kelly said in DHCP Question...:

            @JaredBusch said in DHCP Question...:

            The DHCP range is always the full subnet. That is standard, even if Windows lets you do stupid shit.

            Here is my home router.
            Instead of visibly showing ranges to exclude, outside of windows, you typically tell it hat range to pass out. I'm passing out .31 - .254
            Primary DNS is my PiHole on .4
            Secondary DNS is the router on .1

            ef0668bf-f775-4b9d-af0e-3fa87b13a940-image.png

            Can you clarify something for me @JaredBusch. You stated that DHCP range is always the full subnet, but yours is from .31 to .254. I feel like I'm missing something.

            DHCP always serves the entire subnet it is defined on.

            If you tell it the scope is a /24, it serves .1-.254 always.
            You then subsequently define which part of the scope you want it to hand addresses out on.

            In windows that is done by "excluding" things.
            On most other platforms, it is done by telling it what range to supply to clients that ask for an address. Hence the .31 through .254

            But regardless of what you specify, either as a range to use or range to exclude, DHCP still serves the entire scope.

            This is why you can make reservations outside of the listed range as in my .7 printer and .10 phone.

            When we define the DHCP Scope we can set the delivery IPs define it to 10.100.10.31 - 10.100.10.225 or the like. One does not need to define the scope according to the full subnet whatever that may be.

            DashrenderD 1 Reply Last reply Reply Quote 3
            • DashrenderD
              Dashrender @JaredBusch
              last edited by

              @JaredBusch said in DHCP Question...:

              Here is a shot from Windows Server 2012 R2.

              I have had to explain many times over the years that just because you "exlcude" a range, it does not mean you cannot put a DHCP reservation in that excluded range. Because DHCP is still and always serving the entire subnet defined in the scope.
              42e53403-2096-44be-8f38-4b11d0fa68cb-image.png

              OK - that makes sense since you put it that way. But Windows does allow you to specify things other than the whole subnet, i.e. the whole /24, just like your EdgeRouter does

              4eb377a5-849b-43c0-9f90-de311c4a2ae2-image.png

              J 1 Reply Last reply Reply Quote 0
              • DashrenderD
                Dashrender @PhlipElder
                last edited by

                @PhlipElder said in DHCP Question...:

                @JaredBusch said in DHCP Question...:

                @Kelly said in DHCP Question...:

                @JaredBusch said in DHCP Question...:

                The DHCP range is always the full subnet. That is standard, even if Windows lets you do stupid shit.

                Here is my home router.
                Instead of visibly showing ranges to exclude, outside of windows, you typically tell it hat range to pass out. I'm passing out .31 - .254
                Primary DNS is my PiHole on .4
                Secondary DNS is the router on .1

                ef0668bf-f775-4b9d-af0e-3fa87b13a940-image.png

                Can you clarify something for me @JaredBusch. You stated that DHCP range is always the full subnet, but yours is from .31 to .254. I feel like I'm missing something.

                DHCP always serves the entire subnet it is defined on.

                If you tell it the scope is a /24, it serves .1-.254 always.
                You then subsequently define which part of the scope you want it to hand addresses out on.

                In windows that is done by "excluding" things.
                On most other platforms, it is done by telling it what range to supply to clients that ask for an address. Hence the .31 through .254

                But regardless of what you specify, either as a range to use or range to exclude, DHCP still serves the entire scope.

                This is why you can make reservations outside of the listed range as in my .7 printer and .10 phone.

                When we define the DHCP Scope we can set the delivery IPs define it to 10.100.10.31 - 10.100.10.225 or the like. One does not need to define the scope according to the full subnet whatever that may be.

                Right, in Windows, you have a starting point and an ending point.
                I suppose he's talking about the Length indicator here. That Windows will serve that entire /24 as long as it has data in that range to provide, i.e. the scope or reservations outside of the scope.

                That's cool - I didn't know that, hadn't considered it before.
                713394cb-0cb5-4bcc-aaa2-88dd5b6c58a7-image.png

                PhlipElderP 1 Reply Last reply Reply Quote 0
                • PhlipElderP
                  PhlipElder @Dashrender
                  last edited by

                  @Dashrender said in DHCP Question...:

                  @PhlipElder said in DHCP Question...:

                  @JaredBusch said in DHCP Question...:

                  @Kelly said in DHCP Question...:

                  @JaredBusch said in DHCP Question...:

                  The DHCP range is always the full subnet. That is standard, even if Windows lets you do stupid shit.

                  Here is my home router.
                  Instead of visibly showing ranges to exclude, outside of windows, you typically tell it hat range to pass out. I'm passing out .31 - .254
                  Primary DNS is my PiHole on .4
                  Secondary DNS is the router on .1

                  ef0668bf-f775-4b9d-af0e-3fa87b13a940-image.png

                  Can you clarify something for me @JaredBusch. You stated that DHCP range is always the full subnet, but yours is from .31 to .254. I feel like I'm missing something.

                  DHCP always serves the entire subnet it is defined on.

                  If you tell it the scope is a /24, it serves .1-.254 always.
                  You then subsequently define which part of the scope you want it to hand addresses out on.

                  In windows that is done by "excluding" things.
                  On most other platforms, it is done by telling it what range to supply to clients that ask for an address. Hence the .31 through .254

                  But regardless of what you specify, either as a range to use or range to exclude, DHCP still serves the entire scope.

                  This is why you can make reservations outside of the listed range as in my .7 printer and .10 phone.

                  When we define the DHCP Scope we can set the delivery IPs define it to 10.100.10.31 - 10.100.10.225 or the like. One does not need to define the scope according to the full subnet whatever that may be.

                  Right, in Windows, you have a starting point and an ending point.
                  I suppose he's talking about the Length indicator here. That Windows will serve that entire /24 as long as it has data in that range to provide, i.e. the scope or reservations outside of the scope.

                  That's cool - I didn't know that, hadn't considered it before.
                  713394cb-0cb5-4bcc-aaa2-88dd5b6c58a7-image.png

                  Yeah, that's the ticket. Start IP and End IP settings can be whatever so long as they fall in the subnet mask below.

                  1 Reply Last reply Reply Quote 0
                  • J
                    JasGot @Dashrender
                    last edited by

                    @Dashrender said in DHCP Question...:

                    But Windows does allow you to specify things other than the whole subnet, i.e. the whole /24, just like your EdgeRouter does

                    You can define more than a /24, but not less.
                    In the following pic, you can see the subnet is /24, in the 192.168.100.0 scope.
                    The popout is where you define the DHCP scope to be distributed, not the scope of the subnet.

                    Be sure not to use "Subnet" and "DHCP Scope" interchangeably like M$ does.
                    MS Has you define a scope when you create a new subnet to be served by DHCP, you don't really do anything with the DHCP Scope until you start filling in the Start IP and End IP. No matter how restrictive you make the DHCP Scope (11 to 50 in this case), you will still have a subnet of 255.255.255.0. If you were to make the DHCP scope 192.168.100.1 to 192.168.101.254, you would see the Subnet automatically change to 255.255.254.0

                    66f1e2e3-914b-4cbb-9936-cdbe77b75582-image.png

                    PhlipElderP scottalanmillerS 2 Replies Last reply Reply Quote 1
                    • PhlipElderP
                      PhlipElder @JasGot
                      last edited by

                      @JasGot said in DHCP Question...:

                      @Dashrender said in DHCP Question...:

                      But Windows does allow you to specify things other than the whole subnet, i.e. the whole /24, just like your EdgeRouter does

                      You can define more than a /24, but not less.
                      In the following pic, you can see the subnet is /24, in the 192.168.100.0 scope.
                      The popout is where you define the DHCP scope to be distributed, not the scope of the subnet.

                      Be sure not to use "Subnet" and "DHCP Scope" interchangeably like M$ does.
                      MS Has you define a scope when you create a new subnet to be served by DHCP, you don't really do anything with the DHCP Scope until you start filling in the Start IP and End IP. No matter how restrictive you make the DHCP Scope (11 to 50 in this case), you will still have a subnet of 255.255.255.0. If you were to make the DHCP scope 192.168.100.1 to 192.168.101.254, you would see the Subnet automatically change to 255.255.254.0

                      66f1e2e3-914b-4cbb-9936-cdbe77b75582-image.png

                      News to me?

                      7ef5d752-f831-4741-8749-3c214c1b0111-image.png

                      1 Reply Last reply Reply Quote 2
                      • DashrenderD
                        Dashrender
                        last edited by

                        Exactly - you can definitely declare less than /24
                        d68e5161-18a8-4f14-a5ac-3dde7c466028-image.png

                        You can declare anything that's valid for the given CIDR range
                        My example shows two scopes with /26 subnet

                        1 Reply Last reply Reply Quote 2
                        • scottalanmillerS
                          scottalanmiller @JasGot
                          last edited by

                          @JasGot said in DHCP Question...:

                          In the following pic, you can see the subnet is /24, in the 192.168.100.0 scope.

                          Where does it show that?

                          1 Reply Last reply Reply Quote 0
                          • J
                            JasGot
                            last edited by

                            I guess I am going back subnet school.

                            scottalanmillerS 1 Reply Last reply Reply Quote 1
                            • scottalanmillerS
                              scottalanmiller @JasGot
                              last edited by

                              @JasGot said in DHCP Question...:

                              I guess I am going back subnet school.

                              I found it, it's in the faded greyed out area under the red rectangle.

                              1 Reply Last reply Reply Quote 0
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