Extending IP range in DHCP

jcoleson · 2014-05-15T13:26:07.000Z

I am admittedly a novice, so please forgive my lack of knowledge!

Current condition:

DHCP server(Server 2008 R2) scope handing out 192.168.1.10-254 /255.255.255.0(this was setup prior to me coming here). If more info is needed let me know!

I am running out of IP’s continually. What would be the best plan of action to alleviate this? As I understand I need to change the sub-net. If so what is the best method for doing that?

Thanks for your assistance!!

stoddard · 2014-05-15T13:30:03.000Z

I would just change the subnet mask for /24 to /23. So make it 255.255.254.0. That will give you 192.168.0.1 - 192.168.1.254.

You would need to change it in the DHCP scope, and also on every device in the organization. So switches, printers, your firewall, etc.

stoddard · 2014-05-15T13:33:44.000Z

As far as the order to do this, I would:

First change it in each switch, printer, server, other devices
Change it on the firewall / any routers
Change the DHCP scope
Then after all that add in your DHCP address scope for the new 192.168.0.x range.

Little-Green-Man · 2014-05-15T13:34:44.000Z

You could also create a superscope too:

learn.microsoft.com

Superscopes

jcoleson · 2014-05-15T13:50:09.000Z

This all sounds good! Thanks for the input. Only problem is the current scope will not allow changing the sub-net mask. Will I need to create a new scope for the current network segment and just lose all of my current reservations?

Little-Green-Man · 2014-05-15T13:52:58.000Z

Yes you will need to create a new scope. Once a scope is configured you cannot edit the subnet mask.

jerrysmith · 2014-05-15T13:55:13.000Z

You actually have to delete/deactivate that scope and create a new one. A little nerve wracking but not really a big deal.

I tried to implement a SuperScope once and it was a disaster, it never worked right.

Little-Green-Man · 2014-05-15T14:02:31.000Z

Jerry.Smith:

I tried to implement a SuperScope once and it was a disaster, it never worked right.

That’s right they can be when not setup properly or used in the wrong manner. Last one I saw was replaced because the network it was set up for became too large, and actually caused problems for a guest network implementation. In short, it was used in place of VLANs. Wasn’t pretty at all.

jcoleson · 2014-05-15T14:02:34.000Z

Is it possible to create a new scope and just not make it active until I deactivate the old one? and is this something I could do during regular working hours?

Little-Green-Man · 2014-05-15T14:09:48.000Z

I believe you can, and during the configuration it may ask you if you want to create a super scope (if you choose /23) which allows you to bust up the scopes. You could do this during working hours, but it would require everyone reboot their machines, you reboot switches etc (if necessary) and could be a PITA really quickly depending on how much activity your network has.

Speaking from past experience, it’s much easier to do this after hours.

jcoleson · 2014-05-15T14:15:54.000Z

What do you think of this?

Proposed plan:

Superscope Extending IPs

scope 1 192.168.1.1-254 255.255.250.0(building 1) excluded from distribution
scope 2 192.168.2.1-254 255.255.250.0(building 2) excluded from distribution
scope 3 192.168.3.1-254 255.255.250.0(building 3) excluded from distribution
scope 4 192.168.4.1-254 255.255.250.0(building 4) excluded from distribution
scope 4 192.168.5.1-254 255.255.250.0 (address range for distribution) These would be added to reservations according to location

jcoleson · 2014-05-15T14:17:02.000Z

“PITA” I like that one!

Ethan6123 · 2014-05-15T14:17:47.000Z

JColeson:

Is it possible to create a new scope and just not make it active until I deactivate the old one? and is this something I could do during regular working hours?

Absolutely. This is what you should do. Also remember that your client’s won’t be looking to grab an ip address until their DHCP lease runs out (7 days is the default) so you can do this (DHCP changes) during working hours with little impact.

Subnet changes on the network should be done after hours.

Little-Green-Man · 2014-05-15T14:21:29.000Z

Ethan6123:

JColeson:

Is it possible to create a new scope and just not make it active until I deactivate the old one? and is this something I could do during regular working hours?

Absolutely. This is what you should do. Also remember that your client’s won’t be looking to grab an ip address until their DHCP lease runs out (7 days is the default) so you can do this (DHCP changes) during working hours with little impact.

Subnet changes on the network should be done after hours.

Actually it’s 8 days.

2014-05-15_12_20_17-Scope__192.168.1.0__Theorem_US_Office_Properties.png

jcoleson · 2014-05-15T14:45:52.000Z

I see after more research 255.255.250.0 is invalid 255.255.248.0 is correct. .

Ethan6123 · 2014-05-15T14:51:48.000Z

Yup, 8 days not 7. Thanks Bill.

Little-Green-Man · 2014-05-15T14:52:52.000Z

JColeson:

I see after more research 255.255.250.0 is invalid 255.255.248.0 is correct. .

Yup, here’s a cheat sheet for future reference and a link that could help you out:

http://www.aelius.com/njh/subnet_sheet.html

subnet-calculator.com

Online IP Subnet Calculator and CIDR Calculator

The original fully featured, professional IPv4 network calculators including classful subnet, CIDR and wildcard mask calculators

jcoleson · 2014-05-15T16:41:27.000Z

Thanks for all the help!

Wish me luck!

james-for-microsoft · 2014-05-15T18:18:03.000Z

I have not read all the replies so my apologies if this has already been brought up. Have you worked with the lease times? DHCP by default will reserve an IP until its released after its time is up. You can shorten the lease time to a hour or even less depending on your needs of how many clients you have using that scope.

Little-Green-Man · 2014-05-15T18:18:51.000Z

James for Microsoft:

I have not read all the replies so my apologies if this has already been brought up. Have you worked with the lease times? DHCP by default will reserve an IP until its released after its time is up. You can shorten the lease time to a hour or even less depending on your needs of how many clients you have using that scope.

Good point!