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TCP/IP subnet question

Posted on 2014-02-09
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Last Modified: 2014-03-03
My network is growing.  I am using dhcp and I have almost used all the available host ip addresses.
Everyone has a wifi need on their cellphones and it is adding up quickly.
I need to be able to have dhcp add more than the 254 and still be on my network.
How do I set up the subnet to handle that?
I am currently using 192.168.1.1 - .254 and the router is on 1.1
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Question by:KentBaldwin
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Korbus earned 500 total points
ID: 39845709
The simplest solution would be to expand your subnet mask by a single byte.

Use 192.168.1.1 - 192.168.254.254
You subnet mask would become simply
255.255.0.0

This will give you (aprox) 256*256 total IP addresses you can assign.

You could alternatively expand by only a single bit, which would double your number of available addresses:
Use 192.168.1.1 -192.168.2.254
SNM: 255.255.254.0


Once you make the subnet changes to all the statically-addressed computers, you'll change your DHCP scopes to match it.

Be careful though,  too many devices on the same subnet can hinder network performance.  If this starts happening, you may need to consider breaking your network into separate subnets (one for wifi devices, one for wired workstations and server, for example)
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by:strung
ID: 39845725
I am not sure that is right. My understanding is the Class C 192.168.x.x series of addresses have a maximum of 256 addresses in a subnet. For larger number of addresses, you are supposed to use the Class A or B addresses:

10.0.0.0 - 10.255.255.255
or
172.16.0.0 - 172.31.255.255

See:  http://en.wikipedia.org/wiki/Private_network

and

http://www.cse.uconn.edu/~vcb5043/MISC/IP%20Intranet.html
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Expert Comment

by:Fred Marshall
ID: 39845804
I believe that "Class C", etc. is an anachronism.  Best not think that way.

The private range of addresses that you are using is within:
192.168.0.0/16.

I wouldn't go to that extent however.
I would likely change the network address to 192.168.0.0/23 or 255.255.254.0 .
This will double the number of addresses while keeping the current addresses intact to a point - in that 192.168.1.0 to 192.168.1.254 are all viable addresses within 192.168.0.0/23.

So, if you have a printer with 192.168.1.2/24 then you could change that to 192.168.1.2/23 (or 255.255.254.0) on the printer but any computers pointing to that address would not need to be changed.  Well, except their own subnet mask would be changed of course to 255.255.254.0 but not the printer setup.  Just an example.....

During the transition you may find that everything works pretty well anyway before all the subnet masks are changed.  That can ease transition and is better than a wholesale change of the address range.  The process should start with the DHCP server's own subnet mask and the DHCP lease subnet mask and go from there giving highest priority to the core devices.
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by:Dave Baldwin
ID: 39845809
That "Class C" information is the "old way" of doing it.  The remarks about changing the network mask and DHCP range are correct and would apply even to the other private IP ranges you mentioned.  While the term "Class C" is still used in many places, it is not a technical method.  Classless Inter-Domain Routing (CIDR) was introduced in 1993 to make better use of the IP address space.  This page http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing has a chart that shows how to do subnetting or "IPv4 CIDR blocks".
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Expert Comment

by:vivigatt
ID: 39847782
You can perfectly expand your existing DHCP range/scope with a change in the subnet.

Check these resources:
http://support.microsoft.com/kb/255999

and

http://www.subnet-calculator.com/
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