Home Forums OS X Server and Client Discussion DNS Running out of IP Addresses

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    I’m sure this is a common question and I apologize for being an idiot, but that’s my God given gift, so I guess I can’t complain.

    Things were running really nice here for the last 10 years, one subnet was MORE than enough IP addresses.

    Then we got two carts of iPod Touches. That’s 80 IP addresses…yes, yes, I know, why put them on the Internet? I could go into a whole RANT on that, but I won’t bore you.

    Anyhow, the 80 IP addresses that get sucked up are making some laptops self-assign IP addresses. (Took me a whole hour with Apple Tech Support before >>> I <<< figured out that there were no more available IP addresses from the DHCP server - I deleted a bunch of iPod leases and things went back to normal...that is...until today when I see the iPods in the DHCP list again....evidently just charging them activates the wireless and they get IP addresses again even if NO ONE is using them.) I know how to set up a new subnet on my OSX Server (10.6.2), but I'm afraid it's more than that, right? I mean, don't I have to change the subnet mask so that my File Server ( will be seen by a laptop that's issued an IP of 192.168.2.xxx??? My plan was just to duplicate the existing subnet setup: 1. change the subnet name to 192.168.2.x from 192.168.1.x 2. hand out IPs from to 3. leave the router set to what it is now - it's basically a gateway out to the internet. However, I'm not sure about the subnet mask. Wouldn't I set that for (currently it's Is that all that needs to be done? (It CAN'T be that simple?) I tell you what I'd love to do and that is ISOLATE the iPods to the new subnet, but I'm not sure how to do that. I should be using VLANs and stuff like that, but (see the first sentence above)...I'm overwhelmed as it is. Anyhow...thanks for any help on this. John


    I have no idea what anyone would need 80 iPods for, but is your server box the one doling out the DHCP functionality or are you using a router for this? If it’s a router, is it smart enough to make decisions based on MAC addresses?


    Don’t even get me started on the issue of the iPods. While they are great for lower schoolers, I really did NOT want to put them on the network. But there are some applications that require “calling home” every time the units are started up.

    Right now my OSX Server 10.6.2 is running DHCP and handing out IP addresses. I’d like to keep it so that the server can hand them out.

    I have two routers – one for our cable modem line and one for the T1 line. The cable modem router CAN hand out IP addresses, but I’m afraid that would segment stuff too much?

    But to directly answer your question, YES, I can create IP reservations by mac address. I assume that’s what you mean?



    If you don’t already have one, get yourself an IP Address calculator. I like SubnetCalc.app, or ipnetmonitor.app has one. You can also find Web sites that offer IP address calculators online.

    Familiarize yourself with the different address combinations and results in terms of available IP addresses by altering the subnet mask. I use and we have plenty of addresses plus room to grow.

    If all of your machines and devices use addresses from your DHCP server, you should be able to change the subnet mask and once everything reboots you will have a larger pool of addresses.

    If you have a bunch of machines with manually-entered IP addresses or are doing something special with wireless access points then it becomes more complicated and you’ll have to run around and change a lot of things manually.

    I prefer to have the router distribute DHCP addresses, but it sounds like you have two different things going. Are you using a dual-WAN capable router?

    Assigning IP addresses based on MAC addresses is OK, too, but it won’t help much if there aren’t enough IP addresses to go around. Plus, maintaining the MAC address database can be time consuming as machines come and go. It does prevent unauthorized devices from gaining access to your network, though.


    To actually answer your question — YES it is that simple. You probably don’t want to use a mask of because that is a HUGE network. If you use a subnet mask of you’ll have one network with 1022 host IPs. This mask will give you a network that can use all of these IPs:


    In CIDR notation this network is

    There is a nice on-line subnet calculator here: [url]http://www.subnet-calculator.com/[/url]. You’ll want to look at making “Class B” subnets.


    The subnet calculator makes a lot of sense.

    I just got off the phone with a tech support guy from AdTran and he explained how I need a “supernet” rather than more “subnets”. I see how to do that now.

    Unfortunately, it doesn’t appear that my router (NetGear RP614V4) will support more than a Class C network, so I guess I’m still screwed.

    At least I better understand what I have to do.

    Thanks for the suggestions.



    I’m almost home…

    After numerous discussions w/ AdTran (did I mention how GREAT their tech support is?).

    I need a router that will support a “fractional” subnet (if you will). That is, my router will support subnet mask, but NOT

    In addition once that subnet mask is changed I need to change the physical IP configuration of my DHCP server to match the new subnet prior to creating it on the DHCP server. Otherwise the server throws an error message about the router not being on the same subnet.

    Additionally I’ll have to change ALL my devices that use static IPs to the new subnet mask.

    So the steps seem to be:
    [code]1. Change physical subnet mask of the server to
    2. Expand the subnet on the DHCP server to:
    Starting IP:
    Ending IP:
    Subnet Mask:
    3. Configure the router to handle the subnet with it’s current IP address but change to new subnet mask.[/code]
    It’s taken me two weeks, multiple posts to message boards, some emails to friends and thinking about this for more time that I care to admit. I guess the Internet works ❗

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