Moving to a new DHCP scope

[Jobos]

This school has a /24 subnet but as we have run out of addresses I've been given a new /23 subnet and told that we can still use the old addresses while we move over. What is the recommended method of changing scopes? The school closes in five weeks but I could really do with getting the scope moved before that as I'm very low on free addresses and more machines are on the way.

 

The server has free NIC ports so could one be set to the new subnet so clients can see the server regardless of which subnet they are on or is it best to just hold fire and wait till the summer close down?

[psydii]

Planning.

 

Get a list of all your devices with static IPs.

 

Get a list of all services which access the Static IPs rather than the DNS names. Printer Servers ->network printers are one headache, firewall publishing rules are another, gpo proxy settings are another.

 

Also look in DNS at all your static entries.

 

Figure out how long it will take to manually update to the new subnet. This will determine the downtime window for services.

 

For your DHCP / Dynamic DNS environment, you could set a short lease time, and wait for all clients to have picked this up, then over-night deactive one scope and enable the new one. In the morning everything should be one the new subnet. Obviously your DCs and servers are going to be static, so they need to move over as the first action of the evening.

 

And don't forget about your default gateway and any other routing that may be going on.

[synaesthesia]

You can be lazy if you like, depending on your current scope.

 

Moved one of my primaries to a /22. The /24 they were using was unfortunately at the wrong end, so expanding it means that the server, router and printers etc are all at the end of the scope rather than beginning as would be nice (without changing those too). Not a problem though - router updated, server subnet changed, printers on statics had their subnets changed to 255.255.252.0 and that was absolutely it. DHCP scope moved lock stock to the start of the /22 and doesn't even touch the old /24.

[Jobos]

Thanks guys but getting this done before the holidays is looking like a non starter as Capita haven't sorted out the filtering for the new scope yet, but that said it's probably better for me to wait and take my time anyway.

[synaesthesia]

What a surprise there! (It's no help to you but just a brief anecdote - when we changed our DHCP scope *massively* (i.e. went from 1000 addresses to 16,000 for one scope and another couple of thousand for the statics; nothing like planning ahead!) as well as implementing a complex VLAN infrastructure our new ISP were on it within half an hour. It's good to be with someone who actually want's your business!