Find free addresses in DHCP - Windows 2008

Posted on 2011-04-28
Last Modified: 2012-05-11
Hi - I am running Windows 2008 SP2 (NOT R2)
I need to find out how many more free addresses are available via DHCP on the server to prepare for the installation of a load of new computers.
Is there a utility I can run, either built into Windows or third party that will give me the required information.

thanks in advance
Question by:naifyboy123
    LVL 7

    Accepted Solution

    Open up the DHCP Console under Administrative Tools on the DHCP server and see how many IP addresses are in the pool, how many are excluded and how many have been leased.

    If you only have one subnet in your DHCP scope, then you will only have a maximum of 254 addresses available to lease.

    Check how many servers and computers you have on the one subnet, subtract 254 from this and this will give you how many IP addresses (in a rough way) you SHOULD have available.  

    You need to take into account that some machines/equipment may have multiple IP addresses assigned to them.

    You will also need to take into account the machines with Static addresses applied as these may not show up in DHCP unless you have created a reservation for them.

    Author Comment

    Thanks - I have looked on the console already but cant find where any 'totals' are listed. So I think I would have to manually count them up.
    This is not ideal. As mentioned, I would like a to report on this so I don't have to count them all up.
    LVL 7

    Expert Comment

    I don't know of anything out there that counts your DHCP leases for you.  

    Have you looked at the counters in Perfmon?
    LVL 1

    Assisted Solution

    Slight correction, the maximum number of addresses is not necesarrily 254. This is really determined by how the network segment is subnetted. = 254 hosts = 4094 hosts = 62 hosts

    Though regardless of the subnet the daveforster is right that the Address Pool in the DHCP server will tell you how many host addresses that the DHCP server is handling, minus reservations. The Address Leases under your scope should give you a list of all the active leases. This plus the reservations will give you a snapshot. Take into consideration any machines that are offline at the time of that snapshot to get an idea of max load on the DHCP server to figure how many "free" addresses are left in the DHCP scope.
    LVL 7

    Expert Comment

    Sorry're right!  I was generalising a little too much! :)

    Author Comment

    thanks guys.
    In the end in simply exported as a list, the DHCP scope into a CSV. This showed me the current leases and also reservations. From that I can work out how many I have spare.
    thanks for your help in finding this info.

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