Running out of available DHCP addresses

Hi,

We have a server in the office which is currently providing DHCP for a range of computers on the network, I have reviewed the DHCP statistics and it is showing we only have 14 IP addresses left. After reading further I have discovered there is a possibility of setting up something called a Super Scope which I have never done, can someone tell me how I can go about doing this to provide additional IP addresses on the network?

Thanks in advance.
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Tahir2008Asked:
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James HIT DirectorCommented:
What is your subnet now?
I am assuming it is a class c 192.168.x.x
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Emmanuel AdebayoGlobal Windows Infrastructure Engineer - ConsultantCommented:
Hi,

You have the option superscope or resubnetting. Both of these options require you to make architectural changes to your network.
Superscope
Create a superscope by through the DHCP manager after determine the subnet that you want to use,i.esay your existing subnet is 192.168.0.x, and you new subnet will be 192.168.1.x

Create the scope for 192.168.1.x.
Complete the task by following the steps in the linkbelow

http://www.techrepublic.com/article/create-a-superscope-to-solve-the-problem-of-dwindling-ip-addresses/

Resubnetting
Resubnetting is the recommended procedure for increasing a DHCP scope when the current scope has entirely consumed the current subnet mask. However, this method requires you to change all subnet hosts and gateways. If you have an address range that has run out of available host addresses, you may be able to change the subnet mask to include a larger share of host addresses. However, simply changing the subnet mask requires that all routers and other statically assigned computers be reconfigured and all DHCP clients have renewed their lease obtaining the new parameters.

Additionally, the entire DHCP scope or scopes must first be deleted and then re-created using the new subnet mask. The potential for duplicate addresses exists during this period if you do not take steps to prevent leasing addresses that other clients may use. Despite all of the aforementioned caveats, resubnetting is still the recommended procedure. The resubnetting configuration creates no additional overhead on the subnet routers or gateways, and keeps all hosts on the same broadcast address.

http://support.microsoft.com/kb/255999
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vivigattCommented:
What is the current range of your current scope ?
 If you have 192.168.1.40-192.168.1.139, allowing 100 IP addresses, you can delete this scope and create a larger one using the same subnet, let's say 192.168.1.40-192.168.1.239. Of course, the newly available IP addresses in the scope have all to be available (or you may want to change the IP addresses of the nodes that currently use addresses in the 192.168.1.140-192.168.1.239 range, or exclude them...)
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Tahir2008Author Commented:
The current range is 192.168.67.0-254 on 255.255.255.0

Is it possible to leave the existing scope as is because there is a considerable number of reservations and devices running on the existing scope. I was hoping maybe I could add an additional scope like 192.168.68.0-254 and set the DHCP to start leasing those addresses when it gets full?
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vivigattCommented:
This is not that simple.
192.168.68.0/255.255.255.0 is ANOTHER subnet, so you would have to route packets between both subnets, using a router of some kind. You would also have to set a DHCP relay (often known as "ip-helper") for the DHCP requests (DHCP discover packets) to be forwarded from the 192.168.68.0 subnet to your DHCP server
BTW, 192.168.67.1_192.168.67.254 is the entire 192.168.67.0/255.255.255.0 subnet so, unless you actually do some kind of routing, your DHCP server should be in that range and its IP address must be static and it should be excluded from the scope range. ALso, npote that 192.168.67.0 with a subnet mask of 255.255.255.0 is usually not to be used as the IP address assigned to a host. Even if this is theoretically legit, since 192.168.67.0 represents also the subnet, some routers and other device will not work correctly with a host having said IP address, so it is recommended to avoid using it. Then, your DHCP scope range should be 192.168.67.1-192.168.67.254

In your case, I would try some change in subnetting.
Check this link:
http://www.subnet-calculator.com/
If you use a subnet of 255.255.254.0 instead of 255.255.255.0, you get 510 hosts instead of  252 and the scope could then be:
191.168.66.1 - 191.168.67.254
if you use 172.16.67.0/255.255.253.0 your range becomes
172.16.64.1 - 172.16.67.254 (1022 hosts in the subnet)

You have to change this subnet/subnet mask everywhere, including on the gateway to the Internet, on the DHCP server itself etc. This is not very complex but this is not trivial if you never did it before and you can expect to be doing some mistakes that will prevent your subnet(s) from reaching the Internet or from working correctly. Yet, it is easily fixable so you should not stress too much about it. Just plan to do the change when there are no users, and be sure to perform enough tests to validate that everything works OK.

Check this useful article:
http://www.techrepublic.com/article/get-it-done-ip-addressing-scheme-changes-require-a-cutover-plan/
You'll find more resources googling "change IP addressing plan"
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Tahir2008Author Commented:
Thanks for the helpful information. Am i correct in understanding if I did not want to go ahead and change the IP addressing plan for the complete network I would required a router on the network which would then lease out the new IP addresses from the new scope on the DHCP?

Am I correct in understanding that this would then work as follows:

Server provides DHCP for ranges:

192.168.67.1/255.255.255.0
192.168.68.1/255.255.255.0

The primary router would provide the DHCP leases for the 192.168.67.1 range and a new router would then be installed on the network to provide the new range 192.168.68.1? Also would these addresses start being served automatically when the DHCP scope for 192.168.67.1 is full?
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vivigattCommented:
This is not as simple.
The subnet that a particular host will belong to depends on the port of the switch it connects to or, if wireless, on the access point it connects to.
So are your hosts wired or wireless? or both?
Furthermore, even if routers/gateways sometimes have an embedded dhcp server, in your case, you would certainly want to use a"central" dhcp server, with 2 scopes. The scope a particular host gets its IP address from depends on the subnet it is connected to.
The router to the subnet that your DHCP server is NOT in will just have to relay DHCP discover messages, using a DHCP relay (or ip-helper in Cisco and Procurve world).
Here is how it works:
http://technet.microsoft.com/en-us/library/cc940466.aspx
http://blog.ipexpert.com/2012/04/05/understanding-dhcp-relays/

Last but not the least, with 2 subnets and 2 scopes, you would NOT begin to consume addresses in 192.168.68.0 when 192.168.67.0 is full...

For all these reasons, I really suggest that you consider resubnetting, using 192.168.64.0/255.255.252 for instance.
This is certainly the path of least resistance. No new router. addresses in 192.168.67.x still working.... You would consume addresses in teh entire scope but existsing hosts that already have an address in 192.168.67.x would usually still get the same address (as long as they renew it before the lease expired)
Check the subnet details here:
http://www.subnet-calculator.com/
Remember that  255.255.252.0 is a Class B network (even if 192.168.x.x are usually class C)
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Tahir2008Author Commented:
Another member of staff seems to have completed the superscoping process, still uncertain how this was done but the issue seems resolved now.
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