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I need to expand my internal IP range. Using 192.168.101.xx now and have run out of fixed and DHCP addresses. How do I increase my range on a working network without an outage?

Posted on 2008-10-15
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Last Modified: 2010-04-21
I am using a Windows 2000 server doing DHCP and DNS in an Active Domain environment.  I want to add a new 2003 Server and open my IP range to allow 192.168.102.xx and 192.168.103.xx ranges.  Where do I start and can I do this without buying a router.  I have a switch that is L2 and L3 but don't know much about VLANs or how to set one up.  Current subnet mask is 255.255.255.0 as you might suspect.  Any good suggestions for a new guy on the block?
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by:razorwoods
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You just want both of these /24's to be visible on your flat network ?

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by:that1guy15
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All you need to do is change your mask in the DHCP setting to 255.255.252.0. This will expand your subnet to 192.168.102.1 - 192.168.103.254. You will then also need to update the subnet mask on all statically assigned servers since DHCP will not change those automatically.

Thats it all computers within that range will be able to communicate with each other. You will also need to change the mask on all network equipment too.
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by:lausengdn
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If you don't need to keep them apart you can change your subnet mask to 255.255.0.0
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by:jjmartineziii
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that1guy15 is correct. You may want to look into configuring the switch and using VLANs because you may start to see performance decreases due to an increased broadcast domain.
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by:securedreams_hotmail_com
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I have a HP 5406 switch and it talks about VLANs but I don't understand how that will work.  I still want my 192.168.101 devices to work but want to add the other ranges too.
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by:exx1976
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VLANs are not necessary on a network that size.

that1guy15 almost had it..   You want your netmask to be 255.255.254.0.  255.255.252.0 would give you a network that would span from 192.168.100.0 to 192.168.103.255..


Enjoy!
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by:razorwoods
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Agreed, just change the subnet and you're now broadcasting on the same , thus both ranges will be visible.

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by:that1guy15
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Just by simply changing your mask you will not need to set up vlans. Buy with that many devices on one subnet you might start seeing performance hits.

My suggestion would be to set up two vlans on your network. One for workstations and devices and the other for servers. But you can segregate your network any way you want.

Basically a vlan physically separates your network into separate broadcast domains. Vlans work at layer two. So only devices belonging to a vlan can comunicate with devices on that vlan. Usually vlans are split up by subnets. Like in your case you would have a vlan for the subnet 102 and for the subnet 103.

You will most likley need some communication between your vlans and you can control what is communicated between vlans on your switch.

If you would like help setting up vlans on your switch i can help but I dont work on HP switches often.
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by:that1guy15
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exx1976 thanks for the correction the 252 is a typo.
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by:exx1976
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Again, VLANs aren't necessary on a network of that size..  Expecially if it's GigE..  I have 9 VLANs here that are /21's, and there's no performance issues on any of them.  Granted, the core switches are 6509's with Sup720's and fabric-enabled line cards, but still..   The desktop access switches are only 10/100 2950's with copper uplinks..   :-D
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razorwoods earned 200 total points
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I think all he's looking to do is get both ranges to work and be visible to all machines.

So changing the subnet mask on all member machines is the quickie way to do this.

** as long as you want all the machines on both IP ranges to see and talk to each other.

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by:securedreams_hotmail_com
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Thanks ya all.  I think I may be beginning to understand.  I have a pair of DHCP servers, and a few others that look to a time server, etc.  If I understand correctly - I will basically have to shut everything down.  change the primary server, restart and change the remaining servers in the correct order, all of them going to the 255.255.252.0 subnet mask which will then give me 192.168.100.1 - 192.168.103.255 which is good.  Then I need to run around like a crazy person and change my wireless router and all my other fixed Ip devices.  I also need to tell my DHCP server to start giving out 192.168.102.xx addresses for my PCs that connect via DHCP and I can do that in the "scope"? I still leave my printers and Servers all in the 101 range ( hard coded ) but I do change their subnet mask, Right? Whew!  Gonna have a busy weekend if this is right.  Thanks again everyone.
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by:that1guy15
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The valid ip range will be 192.168.102.1 - 254

You should not need to reboot anything just change IP setting and expand the scope in DHCP.

Depending on if you are changing the DHCP ip range you might need to reboot DHCP clients or refresh their DHCP settings
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by:securedreams_hotmail_com
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I am running 255.255.255.0 now and have 192.168.101.1-255 and am wanting to add about 50 potential new ip addresses for the future growth.  I am trying to open it up to allow 192.168.100.1 thru 192.168.103.255 or equivelent to 4 class c address ranges - all seeing each other as they do now, just moving PCs away from the printer and server ( hardcoded 192.168.101.xx ) range and into the 102 range.  So my concern is which subnet mask do I use for that?  I thought I understood - but guess I am still missing another finer point or two here.  Thank you again forthe clarification.
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by:that1guy15
that1guy15 earned 200 total points
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For that range you will need to use a subnet mask of 255.255.252.0 which will give you a range of 192.168.100.1 - 192.168.103.254.


Here is a link to a subnet calculator that will help you figure out what you need.
http://www.subnet-calculator.com/

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by:exx1976
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+1, that's correct.  192.168.100.0/22 will give you 192.168.100.1 - 192.168.103.254

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by:securedreams_hotmail_com
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Thank you.  I feel more confident about trying it - You're awesome.
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by:that1guy15
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lol

exx1976 so my original typo of 252 I will retract!!. I guess i can just see into the future :)
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by:exx1976
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lol
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