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DHCP Server to give out more than 250 IP addresses on the same network

Posted on 2018-02-09
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Last Modified: 2018-02-13
Hi,

  When we have a WIndows server with DHCP server running, you can make it to give out IP addresses to computers on the network.  Say from 192.168.1.20-250.
  But if your network has, let's say, 350 desktops, 50 network printers and 250 IP phones, somehow you need to make DHCP server give out 650 IP addresses and you wan them to be on the same IP network.
  How do you accomplish that?

Thanks.
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Question by:sglee
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Expert Comment

by:Justin Evans
ID: 42463631
subnetworks in dhcp scope.  so for example you have allocated 192.168.1.20-250,  then you allocate 192.168.2.20-250 and so on.
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Expert Comment

by:Paul MacDonald
ID: 42463636
Change your subnet mask?

If your network is currently 192.168.1.x/24 you have 254 host IPs available to you.  Changing that to 192.168.1.x/23 will give you 512 host IPs.  Changing it to 192.168.1.x/22 will give you 1024 host IPs.

If you're the person in charge of this stuff, you really need to read up on it.  Here's an article from Microsoft about modifying the scope as well.
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Author Comment

by:sglee
ID: 42463658
DHCP 192.168.1.xNew DHCP Scope@Justin
The currnet scope in DHCP server is  [192.168.1.0] as seen in the screenshot.
Are you saying that I can create a new Scope [192.168.2.0]?
Anything else that I have to change? Do I need to make any changes to member servers or network printers that have static IP information?
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Expert Comment

by:Paul MacDonald
ID: 42463712
"Are you saying that I can create a new Scope [192.168.2.0]?"
NO.  Any you really shouldn't be changing this stuff if you don't know what you're doing.

The portion you want to change is illustrated in my screen shot, showing the properties of the existing scope.  You'll have to re-create the scope or create a superscope.  Either way DO NOT PROCEED until you have a better understanding of what you're doing.  You can - and likely will - cause yourself network problems if you don't do several things correctly.
DHCP-example.png
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Author Comment

by:sglee
ID: 42463718
@Paul
Thanks for the information. I will read upon it.
I was just curious about this subject and therefore I posted this question.
I do have a VIRTUAL test server environment where I can try these settings (Windows DC and a couple of virtual machines). The only problem is that, in my test environment,  there won't be hundreds of networks devices that would require IP addresses.
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Expert Comment

by:Paul MacDonald
ID: 42463727
DHCP is very straightforward, but it simplicity belies its power.  You won't destroy anything by misconfiguring DHCP, but you can prevent your clients from getting to your servers (or the Internet) if you don't know how all the pieces fit together.
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Expert Comment

by:masnrock
ID: 42463751
There are multiple ways to go about solving your problem, all of which you should make sure you know what you're doing BEFORE changing. Note I'm providing two suggestions, but that doesn't mean they're the only two ways.

1) Change the subnet mask from /24 to /22, which would give you 1024 IPs. (you might choose something different based on anticipated size) -- Paul made this suggestion.
2) Consider using VLANs. This will limit the sizes of network broadcasts. How you organize this is up to you. If I have a building with multiple floors, I would prefer having a VLAN for each floor. However, that's not the only way to go about it. However, you will also need to make sure to make changes across your switches, as well as get DHCP up and running for each VLAN (you can use your existing Windows server to do this, so don't feel that you have to invest in more equipment or even another server). Another consideration is type of traffic, so having separate VLANs for phones would be something to consider as well.
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Expert Comment

by:Justin Evans
ID: 42463782
@Justin
The currnet scope in DHCP server is  [192.168.1.0] as seen in the screenshot.
Are you saying that I can create a new Scope [192.168.2.0]?
Anything else that I have to change? Do I need to make any changes to member servers or network printers that have static IP information?
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Sglee,  I would strongly recommend you talk to the person in charge of your network IP Infrastructure,  Yes you can create a new scope 192.168.2.0 if that address range is available, and remember to authorise that scope on your Active directory

 ideally you will need to configure Active Directory sites and services to represent your network in Active Directory,  generally you can set a subnetwork for each floor or site in your companies infrastructure,  again go check with your network people.  

 Member servers and network printers that have static IP addresses will be fine if they have already been allocated.    be sure to allocate the scope options for your network,  to ensure Internet connectivity,  including

003 Router,  
006 Dns Servers,
015 DNS Domain Name  
019 IP Layer Fowarding

Please follow the link below for further information,  this applies to windows server 2008 but most of it is relevant to Windows Server 2012

https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-server-2008-R2-and-2008/dd283016(v%3dws.10)
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Author Comment

by:sglee
ID: 42463832
@Justin
Thanks for the information.
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Expert Comment

by:Robert Ornelas
ID: 42464235
Here are the steps i use when doing this.




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.
If you use the resubnetting option, you need to delete and re-create the DHCP scope with the new subnet mask (it is not possible to change only the mask for a particular scope). If you are servicing existing clients within a portion of this range, you should turn on conflict detection until all your clients are migrated into the new scope. This action requires you to perform the following steps:
1.      Configure the interface of each connected router and change the IP address for the connected interface, its subnet address, and its subnet mask.
2.      Delete your current DHCP scope.
3.      Create a new DHCP scope with the new subnet mask.
4.      Enable the Conflict Retries option on the DHCP server (set to 1 or 2).
5.      Force your DHCP clients to renew their DHCP leases.
6.      Change the IP address, subnet mask, and/or default gateway on each statically-configured host.
7.      The following example shows the result if you use the resubnetting option:
8.      Subnet Address: 192.168.100.0
Subnet Mask: 255.255.254.0
9.      You now have a network of 510 hosts with addresses from 192.168.100.1 to 192.168.101.254 (for scope 192.168.100.0), or 256 newly available DHCP addresses.
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Expert Comment

by:arnold
ID: 42464624
There are several ways to facilitate the connection of more than the 253 devices on a network.

One as you've discussed is to increase the scope of ip subnet.
The other option depending on the environment is by separating the various items onto their own segments
One DHCP with ip helpers configured on the switches can allocate IPs from multiple/several segments.

Ip super scopes.

Distinction, increasing the scope of the existing ip sunset, requires updates on all devices to avoid netmask mismatch ..
Adding a segment/s might be simpler by adding those segments to the router, then ...
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