DHCP Subnet Change

[karldenton]

Hi,

At present we have a superscope in DHCP (not my setup)

10.10.6.0 = computers, servers switches

7.0 - 10.0 not really used

 

However each scope EG 6.0 has subnet mask of 255.255.255.0 so only 254 devices. I'd like to extend one of these.

 

I've copied the dhcp file over to a non-domain test server to play about with it. If I delete the 7.0 and the 6.0 I can then create a new 6.0 with 255.255.254.0 giving me 510 devices through to 7.254.

 

The DC's are virtual.

 

What is the best way of doing this in production as once I delete the scope nothing will be able to connect to anything until I recreate it and all the options such as router, dns etc.

 

Thanks

[karldenton]

Well I've just followed Increasing the number of IP addresses in DHCP scope – windowstricks.in and got it working.

 

It creates the new Scope outside of the superscope though. Does that matter?

 

It also involves deleting the old one so will be some downtime. Just need to pluck up the courage to do it in production.

 

I'm presuming once I've done that all I should then need to do is change the subnet mask on all the servers and switches

[ADMaster]

I think I would just do it, anyone already connected should stay connected, it just won't give out new addresses while your making the change.

Take a backup of the dhcp settings.

Figure out all the netsh commands to recreate the scope with all the correct options.

Write it out in a batch file or paste it into cmd so you have very minimal downtime.

Do an ipconfig release renew on a test workstation, if it works great, if not restore the backup and figure out what went wrong.

I've changed dhcp scopes a few times over the years. Depending on the change and how quickly I want it to take effect, I decrease or increase the lease time. Then wait and make the change. I would also make the change at a time with minimal use such as after classes are done for the day, or before students arrive.

https://technet.microsoft.com/en-us/library/bb490941.aspx

[mukz]

Superscopes are recommended on Server 2016. Ideally create a new DHCP server if you cant do it out of hours.