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Subnet question. Need the correct subnet mask.

Hi,
I need to add more addresses to the DHCP pool.  We have completely exhausted the 192.168.0.x range.  I am trying to find the best most efficient way to expand the pool.  We are using Windows 2000 server providing DHCP and DNS.  All current addresses are in the 192.168.0.x 255.255.255.0 segment.  I would like to expand the address pool to at least double or even quadrupal the number IE 192.168.0.x, 192.168.1.x, 192.168.2.x, 192.168.3.x but I dont know how to limit the subnet mask to just allow these numbers.  For some reason I just dont get the mask portion...can some one tell me the correct mask to allow just these four segments?  Is there a better way?  I dont have extra routers and I would just like to use what I have to expand the amount of IP addresses.  Please help.  

Clueless
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zeroiq01
Asked:
zeroiq01
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1 Solution
 
Rob WilliamsCommented:
Changing the subnet mask to 255.255.252.0 would allow you to use from 192.168.0.1 to 192.168.3.254  (with a network ID of 192.168.0.0 and a broadcast address of 192.168.3.255)
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mav7469Commented:
There are a few questions first.. How many segments are on your network?  Easiest way to think of this is how many different sites or Local Area Networks do you need?  Once you have that, then we can better answer your question.

Thanks

Mav
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zeroiq01Author Commented:
ok,

we have one subnet that is full for the entire company 192.168.0.1-254 255.255.255.0.  I need to get more addresses.  I need the most efficeint way.  the way it stands now.

---firewall\vpn\router 192.168.0.1
---2000-server DHCP 192.168.0.8
---180 clients 192.168.0.31-220 DHCP
---wireless router 192.168.0.3 passes DHCP 192.168.0.221-239
---44 addresses 192.168.0.1-30 reserved (Servers/swiches), 192.168.0.240-254 reserved (printers/copiers/fax)

I need the best way to get more addresses.

i thought of:

192.168.0.x reserved for servers /printers /switches /admin
192.168.1.x front office cubes 100plus clients and growing
192.168.2.x fab computers 80+ clients and growing
192.168.3.x wireless access points. we are adding at least one if not two.

problem is one. Ive never done this before and two i dont have seperate routers for each of the switches.  I currently have 4 hp 4000m switches with 64 ports apiece
and one 48 port gig switch.  What I need is the ability of all devices to see all the servers and printers,  currentely located at 192.168.0.4-29 and 192.168.0.240-254.  What is the best way to do this? seprate nets (like above) or just expanding the DHCP pool and reserving?

clueless
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knightrider2k2Commented:
Robwill is correct. Just configure your dhcp server for (255.255.252.0) subnet and use this subnet on all your servers and routers. They will come under 1 broadcast domain.
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Rob WilliamsCommented:
You can put it all under one subnet and all will work fine, but you could get better network performance by breaking it up into multiple subnets and adding routers.
Regardless, when you are ready to make the change, make sure you do some planning as the subnet masks will have to be changed on all devices. Shorten your DHCP lease times beforehand so the changes will take place quickly. and make note of all statically assigned devices so that you can make the change quickly with no over-sights.
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jpdaveyCommented:
Not that this will impact your overall plan, but one small problem with your "I thought of" comment is that you won't be able to make (short of static addresses or reservations) the DHCP server hand out, say, 192.168.1.x addresses to the front office cubes. Any DHCP client will grab whatever DHCP address the DHCP server feels like handing out at that time.

Segmenting would rock. Is it possible that your switch is a layer three switch (it does routing). Or if it does VLANs you could cordon off your .0, .1, .2 and .3 networks that way...

Whatever you do, RobWill's last comment was right on target.

JP
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lrmooreCommented:
All the above is logically correct, but I would be remiss if I did not point out that changing the subnet mask on your 192.168.0.0 network to 255.255.252.0 is not technically a subnet mask. It is technically a supernet mask because 192.168.0.x is a Class C network.
While it makes perfect logical sense, not every device IP stack recognizes anything other than classful masks or subnet masks. Old printers, old Windows 9x boxes, older IP devices may simply not work. Not all applications will allow you to designate the IP address of server or client in anything other than classful masks or subnet masks.
Most of the newer stuff that recognizes classless addressing (CIDR) will be fine. Most of the older stuff will not.
My suggestion would be to change *everything* to a real Class B private subnet like 172.168.122.0/23
172.168.122.1 - 172.168.123.254
Mask 255.255.254.0
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lrmooreCommented:
oops... correction to the above:
>172.168.122.0/23
172.168.122.1 - 172.168.123.254

Should drop the "8":

172.16.122.0/23
172.16.122.1 - 172.16.123.254
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jpdaveyCommented:
So adding host range to the class is a supernet mask and subtracting host range is a subnet mask? Interesting!
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Rob WilliamsCommented:
Thanks zeroiq01,
--Rob
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