Adding another IP Range to DHCP

[Nick_Parker]

Our DHCP is set to assign IPs with the following settings:

IP: 192.168.0.x
Subnet: 255.255.255.0

With a lease time of 7 days (to try and stop old addresses from filling up the leases etc...)

According to the scope statistics, we only have 4 addresses left, which is a problem, because 20 new laptops have just arrived (40 potential IP leases, one for wired, one for wireless)

What is the best way to go about adding another range to our DHCP server?

I read somewhere on this forum that one method would be to add another range of 192.168.1.x
and to change the subnet on both ranged to 255.255.254.0

Is this correct?

Thanks for your help!

[tmcd35]

Is there a reason for currently using 192.168.0.x, apart from it being a well used private range? Are you now deeply tied into using this range - ie, loads of servers/switches/ap/printers/etc with static IP's that'd be a complete arse to change?

If not then you may want to consider switching to class B addresses: 172.16.x.x with a subnet 255.255.0.0 - This'll solve your problem not only for now but far, far into any forseeable future, which must be a good thing.

[Nick_Parker]

There are a few static printers/switches/APs, however, if your recommend this as the best option, then i'm happy to spend a weekend changing them over...

Would this mean anything in the 172.16.x.x range is valid and viewable?

[tmcd35]

Exactly, this give you something like 65000 valid IP address. If it was my network I'd split these further into logically smaller subnets and only allow the DHCP server to lease a small number of IP's. Thus:

say - 172.16.1.x for servers
172.16.11.x for switches
172.16.51.x for AP's
172.16.101.x for DHCP - everything outside of this range is excluded in the DHCP server. If I need more than 256 leases, then I'd un-excluded the 172.16.102.x range.

Remember, because the subnet mask is 255.255.0.0, that everything on all the above ranges can see each other, your not making actual physical subnets, your just making it easier to manage your IP's. You could try and work out better subnet mask to shrink the available range of IP's, but unless you paranoid about others hacking your network it's rearly not work it.

Also, I've noticed your DHCP lease is 7 days. A bit long if you ask me! Are all the computers in the school likely to be on at the same time? Our lease here is a couple hours (i think). So when a laptop is switched off it's address is freed for another machine. Reducing your lease time could in itself create the extra IP's you need without extended/changing your current range.

We have to pay for our IP ranges from county here. They use the 10.x.x.x class A subnet and 'sell' us a subnet for our school from within that range. This means when (were close) run out of IP's (again) we have to pay for another range! I did set up a NAT sever and use my own class B IP's the last time we ran out, but county did not like my solution! I'd give anything for the freedom of my own totaly private subnet.

[FN-GM]

What you have to pay for the IP address? that’s robbery!
We are fine here, well within our range. We use also use 172.
Our range is 172.24.32.0 – 172.24.35.254

[tmcd35]

What you have to pay for the IP address? that’s robbery!

Tell me about it! Part of using our LEA as our ISP...

[zag]

Paying for internal IP addresses?? Now I've heard it all

Just increase your subnet to .252 instead of .255, that will give you 1000 extra IP's right away.

[raufdean]

Just increase your subnet to .252 instead of .255, that will give you 1000 extra IP's right away

Absoulutley. 2 second job.

Just have to add my incredulity at the fact that you're paying for private IP space..

Rauf

[projector1]

Paying for internal IP addresses?? Now I've heard it all

Just increase your subnet to .252 instead of .255, that will give you 1000 extra IP's right away.

the good old CIDR (classless interdomain routing!)

[cookie_monster]

A few LEAs do this now (and some charge for it) so that all of their schools are on a semi private network, i don't think we do under EMBC but i'd have to check the details of the package. I'm not totally surprised that they would charge for more addresses as they would then have to pass on the work to Fujitsu or whoever to make the changes and they wouldn't do it for free i suspect. County hate it when you use a NAT box as it gets in the way of their plan for world domination (and they can't nosey into your network), they also point out that all of the great services that they 'DON'T' offer will be degraded by using NAT.

As you're using your own internal IP range the suggestion of a custom net mask is a good solution.

[Geoff]

If you are in one of these brain damaged LEAs that charged for private IPs, I suggest you grab a NAT firewall (Smoothwall express, IPCop, DIY Linux, ISA server) and do things that way. If you have anything that 'needs' to be addressable externally, you can use the DMZ functionality.

Cheaper in the long run and more secure.

[Nick_Parker]

Paying for internal IP addresses?? Now I've heard it all

Just increase your subnet to .252 instead of .255, that will give you 1000 extra IP's right away.

If I change the subnet to .252
What IP ranges are then usable?

[Nick_Parker]

Never fear, figured it out, found a very nifty site, helped me work through my moment of dimness!

http://ipcalc.nmonitoring.com

Thanks to everybody that helped and thanks for all your suggestions!

[Nick_Parker]

I have another query please,

If i setup multiple Scopes, how does the server know which one to lease addresses from?

[Grommit]

We have to pay for our IP ranges from county here. They use the 10.x.x.x class A subnet and 'sell' us a subnet for our school from within that range. This means when (were close) run out of IP's (again) we have to pay for another range! I did set up a NAT sever and use my own class B IP's the last time we ran out, but county did not like my solution! I'd give anything for the freedom of my own totaly private subnet.

All you do is get a server and put in 2 network card... Put the 10.x.x.x facing the LEA and then the 172 internal and then set the DHCP to 172..

You then have your own range