Expanding the IP range on an existing network


  • Service Provider

    So over in this thread, it was mentioned that expanding the OP's current subnet would be the better way to go.

    The following two things were said, and I wanted to expand on them.

    @Dashrender said:

    1. change your IP to a /23 or /22 - this will require updating all of your current equipment with a new Subnet Mask.

    @scottalanmiller said:

    Not range related. You are changing your subnet mask. So if you are /24, go to /22.

    For the purpose of this example, I am going to use the good old 192.168.1.0/24 that no one should ever be using in their business.

    As we all know a /24 gives us 256 IP addresses of which we can use 254 (.1-.254).
    0_1455828640537_2016-02-18 14_49_39-Online IP CIDR _ VLSM Supernet Calculator.png

    In this type of setup, most people have their router using 192.168.1.1 and all the devices had the netmask set to 255.255.255.0.

    When you expand a network from a /24 to say a /23, you suddenly have access to 512 IP addresses, of which 510 are usable.
    0_1455829037359_2016-02-18 14_55_51-Online IP CIDR _ VLSM Supernet Calculator.png

    Due to the arcane arts of binary, you also expand downward on the third octet, but that is a lesson for a different post.

    Now that we have that background information I will get to the reason I copied in those responses above.

    When you expand your network, it is a common fallacy to assume that it is a huge thing requiring reprogramming all of the things. This is simply not true. The only device that is required to be updated is the router itself and on top of that only the netmask needs updated. That is it. So our router will still be on 192.168.1.1 with an updated netmask of 255.255.254.0 or a /23 if your router uses CIDR nomenclature.

    All of your existing devices will continue to work unchanged on their original /24 netmask because the router is still within their IP range.

    You can immediately add new devices to the expanded range, but you will be need to avoid using 192.168.1.0. Now the devices you put in the new range, will be able to talk to the router because that is withing their netmask. What you will not be able to do is communicate with any device above 192.168.1.1 that still has the original netmask because that is outside of the old netmask range and the device will send it to the router instead of the device.

    But what this does is allow you to expand in a planned and controlled fashion. In the case of the original post, they can simply select a range of IP addresses to be used for the phones and set them up without affecting the existing network.

    You can then take your time and plan out the schedule to update your DHCP scope and then the various fixed IP devices for the new netmask.

    Readdressing your network is not a super hard thing. It just takes a little knowledge and planning.



  • JB does have a good point here.

    But things that will need to have their Subnet mask changed more quickly that others are - servers and printers.

    Any devices in the 192.168.1.x range won't be able to talk to those old servers and printers, or more correctly, your new device will be able to talk to them, but the old won't be able to respond correctly.

    In the case of putting phones up in that new higher range, this is probably not that big of a deal, but if you have laptops, desktops etc... now you problems - not insurmountable ones, just something to deal with.


  • Service Provider

    @Dashrender said:

    JB does have a good point here.

    But things that will need to have their Subnet mask changed more quickly that others are - servers and printers.

    Any devices in the 192.168.1.x range won't be able to talk to those old servers and printers, or more correctly, your new device will be able to talk to them, but the old won't be able to respond correctly.

    In the case of putting phones up in that new higher range, this is probably not that big of a deal, but if you have laptops, desktops etc... now you problems - not insurmountable ones, just something to deal with.

    Correct, you would want to change your servers first. so that devices in the new range can get answers back.

    In my case, printers are always DHCP reservations. So as soon as I update the DHCP scope that will come down.



  • @JaredBusch said:

    Correct, you would want to change your servers first. so that devices in the new range can get answers back.

    In my case, printers are always DHCP reservations. So as soon as I update the DHCP scope that will come down.

    I've seen you post that before - I think I need to adapt that.


  • Service Provider

    @Dashrender said:

    @JaredBusch said:

    Correct, you would want to change your servers first. so that devices in the new range can get answers back.

    In my case, printers are always DHCP reservations. So as soon as I update the DHCP scope that will come down.

    I've seen you post that before - I think I need to adapt that.

    Everything is DHCP reservations except the core server infrastructure, HOST, DC, DHCP, and the Router. Exverything else is DHCP reservations, Printers, secondary servers, PBX, everything. Desktops and phones, just normal DHCP.



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