Additional DHCP scope

I currently have a Windows 2003 network just about filled to the brim of 128.100.0.x / 255.255.255.0
I would like to set up a either a 2nd scope of 128.100.0.1.x if thats possible, that can talk to everything on the original scope. I'd prefer not to have to create a whole new scope with completely different IP addresses because we have a few static IPs floating around on devices. The firewall is a PIX 515e but its not acting as a DHCP server.
What are my options and whats the easiest way to get more IP addresses? Thank you.
nzv101Asked:
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naomelixesCTOCommented:
First off, since those are private addresses, you'd be better off assigning them a private range (192.168.x.x, 10.x.x.x, or 172.16.0.0 to 172.31.255.255). Of course, the probability of you having problems is very low (you will probably only have them if you try to communicate with 256 of the billions of IPv4 addresses in the world), but still... It's cleaner.

As for the question: just enable another scope (128.100.1.0 with the subnet mask of 255.255.255.0, for example) and then setup the routes between both networks (128.100.0.0/24 and 128.100.1.0/24).
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smangognaCommented:
128.100.0.1.x  ??

I suggest to change your subnet mast to 255.255.0.0 so you can have 128.100.x.x networks

Sergio
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simpsolCommented:
Maybe I am misunderstanding. IPV4 address can only have 4 octects and since you are using a Class C Address (255.255.255.0) you will have to either change the subnet mask to allow more hosts or create a new subnet and then route traffic between the two subnets.

From your post above it seems there are five octects 128.100.0.1.x which is not possible. The 128.100.0.x and 128.100.0.1 with subnet of 255.255.255.0 are referring to the same network

Please clarify
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naomelixesCTOCommented:
If you prefer to change the subnet mask of the dhcp scope, I would change it from 128.100.0.0 with a mask of 255.255.255.0 to 128.100.0.0 with a mask of 255.255.254.0, as that will restrict addresses to 128.100.0.0 through 128.100.1.255.
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nzv101Author Commented:
Sorry, typo,  I meant to say 128.100.0.x and 128.100.1.x as two different subnets.

How would I change the mask to 255.255.254.0 without disrupting anything in place? A range of 128.100.0.0 - 128.100.1.255 will give me an additional 255 IP addresses and that will last me for years.
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naomelixesCTOCommented:
What is running DHCP? A Windows server? A network device?
It really depends on the DHCP server and how it is setup... Some low-end products have DHCP servers with only a limited number of options and clients, but any semi-capable DHCP server will support this change.
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nzv101Author Commented:
DHCP is running on a windows server 2003 SP1 machine.
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Lee_YCPCommented:
Three options:
1.  As naomelixes suggestes:  You change the subnet mask on all the current devices to 255.255.254.0.  Then you change the DHCP scope to include 128.100.0.1 - 128.100.1.254 and use the 255.255.254.0 mask.  It is a simple enough change and it does not require you to change any IPs, so you have to get into DNS issues.   But you will have to change each device that uses a mask.
2.  As smanqoqa suggests:  Similar to option 1, you change your mask to something like 255.255.0.0 and probably never run out of IPs again.  Same impact as option 1.
3.  You leave everything the way it is.  Setup a new scope in DHCP with 128.100.1.0 network with a 255.255.255.0 mask.  Create subinterfaces on your gateway router.  One subinterface will be the current ip on that interface and the second subinterface will be an IP in the new scope and ultimately the gateway for that subnet.  That router will then be able to provide a route between the two subnets.  The new subinterface will also need to forward DHCP requests or you will need to multi-home your DHCP server or let something else serve DHCP in that new subnet.  

Note:  If the PIX is the only thing doing your routing, someone else will have to comment on its ability to do subinterfaces.  If the PIX is the only thing doing your routing, what do your collision domains look like?
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nzv101Author Commented:
For option 1, from what I can tell, the only way to do that is to delete the current scope then create a new one so they don't overlap. Is that right?
Can the current scope just be deactivated or modified to have the new mask?
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naomelixesCTOCommented:
I think that is correct. I can't access a 2003 DHCP server right now to be sure if you can just change the running scope.
Don't forget to manually change the mask in any static IP devices, or they won't communicate with the "old" network.
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simpsolCommented:
I disagree with just changing the DHCP Scope as in the orginal post the user said that he has devices with static IP address. If you change the Subnet mask you will have to manually go and change the subnet mask on each of those devices which has static IP address. If you only have a handful then it is doable, but if they are at different sites then it is something you need to consider.

If the DHCP Server is a window server ehn set up reservations for the devices having the Static IP address and manage them using the DHCP server.
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nzv101Author Commented:
I may end up resubnetting, but first I have to talk to some people and find out exactly where all the static devices are. We only have a couple sites that are near each other, but there's a lot of device creep around here.
Is there a way to dump all the existing leases, reservations and exclusions into a new scope or do I have to enter them all in again manually? Even if I deactivate the scope and try to make a new one, I think dhcp just tells me it will overlap, so I have to delete the whole thing, and don't want to type in everything again manually.
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smangognaCommented:
I think the the optimum vould be to buy layer3 switches and create VLAN so you don't have to change any of stati ip addresses, you can create different vlan for different floor or building, and you optimize your network, you will reduce drastically broadcasts.
And please use private classes for the new vlan.

Sergio
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Lee_YCPCommented:
Until you weigh the options and decide, you may consider reducing your DHCP lease period to provide the most available IPs at any given time.  Remember windows starts midperiod seeing if it can renew its IP address, meaning if you have a 7 day lease period, windows will try to renew at 3.5 days.  In contrast, if the machine boots, grabs an ip from DHCP, then shuts down, DHCP would not cancel the reservation for 7 days.  So having a smaller renewal period may keep as many IPs free as you can.
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nzv101Author Commented:
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