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Expanding DHCP scope.

I have a Server 2003 R2 DC and also a secondary DC. My issueis that i am running out of ip's on my scope. My scope is 192.168.25.66-192.168.25.199. The ip's outside the scope are almost completely used for static network devices, servers, etc. I need a way to add an extra subnet and scope and use my 192.168.25.X subnet for static IP's and 192.168.26.X for DHCP. How would I go about this. There is no way that I can change all the subnet mask on all of the static network devices.
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bryangoss
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bryangoss
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lucius_theCommented:
You need to either:

a) extend your current subnet
change the subnet value on all devices that have statically configured IP addresses from 255.255.255.0 to 255.255.254.0. NOTE that this way you will get adrress ranges from 192.168.24.1 to 192.168.25.254 in your subnet. So move the DHCP range to 192.168.24.X instead of 192.168.26.X and problem solved.

b) dual-home your server - add another IP address range on your server and define a DHCP there. Note that this way you need routing to get from one subnet to another. Case (a) does not need a router, all devices will see each other directly on the cable.
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lucius_theCommented:
When configuring DHCP server for case (a), you need of course to reconfigure your DHCP server to issue addresses with subnet value of 255.255.254.0 otherwise not all equipment will be able to talk to each other without a router.
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bryangossAuthor Commented:
RE:
b) dual-home your server - add another IP address range on your server and define a DHCP there. Note that this way you need routing to get from one subnet to another. Case (a) does not need a router, all devices will see each other directly on the cable.


RE: Does this require a second interface on the server? Is there a tech article on this process? I can take care of the router side. What are possible issues that I might face or some of the concerns?

Is it better just to change the subnet mask on the scope, even though it would be a major headache. Has anyone had to face this same issue, if so, can I have some opinions?
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lucius_theCommented:
You do not need an additional interface on the server, go to your network adapter, open TCP/IP properties, click Advanced, and then click Add under "IP settings" tab. This way you can have more than one IP address on the same interface.

If you choose this path, you will need to route packets from one subnet to another. Your server will be able to communicate with both network subnets. Also, you can do this trick on your other devices. But this is an unclean solution, I wouldn't recommend it, especially if you have workstations communicating directly to each other.

Perhaps you can can also lower the DHCP lease time, which is 3 days by default, I think, so this might help if you have a lot of users that come and go (notebooks etc).
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bryangossAuthor Commented:
So from what I gather is that it is best to just change the subnet mask on the dhcp scope. So if I change from 255.255.255.0 to 2555.255.252.0, my network will expand from 192.168.25.1-254, to 192.168 24.1 thru 192.168.25.254. Is this correct? What is the best way to go about the change, and is there a step by step on this, so I'm not trying to fix server problem at the same time as chnage subnet mask on all static network devices?
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lucius_theCommented:
Ok, first, if you change your subnet from 255.255.255.0 to 255.255.252.0 you will get IP range from 192.168.24.0 to 192.168.27.0. Use an online subnet calculator (like this one http://www.subnet-calculator.com/subnet.php?net_class=B) to see what you would get.

So, whatever you choose to get a big enough address range is ok. Be sure not to go too far with this. Ethernet broadcasts can slow your network down if you have a lot of users on the same network segment (I mean ethernet segments here, it won't help if you add two IP segments).

That being sad, just change the subnet mask, say, to 255.255.254.0 on all devices that use static IP addreses. One by one, communication won't be lost, maybe just during the change, but will work immediately after the change is done. You don't have to change all at the same time, go one by one and test to be sure. After that, change DHCP setting to start issuing IP addreses in range 192.168.24.0-192.168.24.254. That's it.

One note - before you do anything check that your DSL router, or whatever you are using, supports subnets other than 255.255.255.0. It is very possible for cheap SOHO routers that you won't be able to expand the subnet to 255.255.254.0 and therefore you will need to upgrade the router to a better one to allow devices on 192.168.24.X to access the Internet.

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