2 DHCPs for redundancy?

[Digitalcandy]

I've got a single site LAN with no routers and ~120 DHCP enabled computers/devices. I would like to implement DHCP on my second of two AD servers, but I am very low on IP addresses due to Windows VPN and Dial-up access (20 total reserved). I inherited a LAN that leases out IPs from;

192.168.0.10 to 192.168.0.199
subnet = 255.255.255.0


I need to free up IPs for my second DHCP server but as you can see, I only have ~189 total. Should I change the subnet to 255.255.0.0 to give me a butt load more? I know I'd also have to change non DHCP IPs such as firewall, switches, servers, printers, etc...

 

[JAC5528]

Are you using the addresses from .200 to.254? If not, you could open up those address on the current DHCP server or create another DHCP server and include just those address. Make sure all the scope options are the same for the second DHCP server.
Good Luck.

 

[markdmac]

If splitting your scope you will need to have enough IPs available on each server to service the clients.

I think you are on the right track and should change the subnet mask to allow you to take advantage of more IPs.

I hope you find this post helpful.

Regards,

Mark

 

[Daveyd123]

or else change to the 10.x.x.x network

 

[Digitalcandy]

JAC5528:

Yes, I am using IPs 200 - 254. I'd rather not change to the 10.x.x.x network because it would require 20-30 manual IP changes on switches, printers, and other machines. I suppose I could do it, and the best time would be Christmas week since we will be closed.

 

[dbMark]

Be forewarned that some routers cannot be configured for all classes. So a $100 router may not be capable of more than one 192.168.x.x range of 256 IPs unless it specifically says so.

Class A - 1 to 127
NAT ranges 10.x.x.x
Mask min.: 255.0.0.0
Network can access 256x256x256 IPs

Class B - 128 to 191
NAT ranges 172.16.x.x to 172.31.x.x
Mask min.: 255.255.0.0
Network can access at least 256x256 IPs

Class C - 192 to 254
NAT ranges 192.168.x.x
Mask min.: 255.255.255.0
Network can access 256 IPs (actually only 253*)

* A network cannot use 3 of available addresses for connected devices since these need to be reserved for network use: router IP, 0=network, 255=broadcast.

Therefore if you still want to use 192.168.x.x past 256 IP address, then you'll probably have to split your network in two? I'm not sure if your one router will allow multiple 198.168.x.x networks... Or try Class B configurations. Just be sure your router can handle Class B. Many routers don't even tell you which classes they can work with, but not all were designed to use Class A or B. If you have to buy a new router, verify its capabilities before you buy.

(I got burned once when I bought a $170 "small office" router that did not say anywhere which classes it could run, although I must admit all the examples did use Class C (192.168.x.x) ranges. I just assumed it could do any of them. I tried to configure it as 172.16.x.x but it wouldn't do it. It worked only for Class C. I guess it was designed only for the home or small office environment, not for mid-size companies.)

 

[AdminGreg]

The easiest way to increase the amount of usable IP addresses on your network would be to use a class B subnet mask on your class C network.

subnet - 192.168.1.0
mask - 255.255.0.0

I beleive that was your original idea, correct?
That would give you a grand total of 65536 host IP addresses (including network and broadcast).

 

[Digitalcandy]

AdminGreg:

Correct; however, I would still have to go around and manually change the subnet mask on 20-30 devices. I may as well switch to class A network 10.x.x.x.


dbMark:

I have no routers on my LAN other than our SonicWall firewall if that's what you're referring to. As stated above, I'll be switching to class A network so I don't mix a class B subnet with a class C network.

 

[Seaspray0]

Or how about this sollution. Get a router and split your LAN. Now you'll have 2 class C's to work with. You could put the second server on the second segment. Move 1/2 of your computers to the second LAN and leave the fixed IP's on the first LAN. If you allow the router to pass boot-p then you could have each server able to pass DHCP to both segments. Have 1 DHCP server cover the bottom half of the scope and the other cover the top half of the scope.


A+/MCP/MCSE/MCDBA