A Second Domain/Network on the same subnet

[Mr.Ben]

Hi Guys. I am after some advice

 

I have just procured a shiny new server to start building a brand new network with. The existing server installations here have a few problems (dating back before my time!) that make me think that I should start afresh with a new domain and gradually move users and services across to it. The timescale here is about 5 months to do the job. (Month one & two for the planning/build/testing, 3 for training/documentation/ 4 for rollout and 5 for stabilization).

 

It is the first time I have had the chance to build from the ground up whilst migrating and the first issue that I have thought of would be how to move DHCP from the old servers to a new one.

 

My first thought was that I could (for a short period), assign static IP's to all machines so that they continue to see the old domain and use it's dns, whilst bringing up a new dhcp instance on the new server (the static addresses would be excluded from the range). Is there a better way of doing this?

 

I will then create a trust between two two domains to allow for access to information!

[Jamman960]

You could just use the 1 DHCP server until you switch the old one off at which point you'd just need to ensure that all reservations/exclusions are in place and then just switch off the old and authorise the new one - when clients next need to get an IP address they'll get assigned an address from the new server. As long as the old DHCP server gives out both DNS servers to clients you should be fine.

[pritchardavid]

another idea you could do

 

Make your scope on the old domain a bit smaller and that way you can get a scope running on the second domain, has you have some spare ip address

[GrumbleDook]

Instead of using static addresses use DHCP reservation on both servers so that you can migrate only those machines you want across, when you want to.

[EduTech]

Yeah, I have done this in the past for a demo environment. All you have to make sure is you don't have 2 DHCP Servers on the network dishing out IP's as you know you'll get problems

 

Have Fun!

 

James.

[Mr.Ben]

Thanks for all the suggestions - I've gone with DHCP reservations as the plan so a big thanks to Tony for reminding me that I can do that!

[GrumbleDook]

To be honest, I prefer folk to use DHCP reservations anyway ... it allows for a better audit trail if something should go wrong and someone needs to investigate something.

[bart21]

I agree. I would use reservations.

[powdarrmonkey]

I would not. My approach would be to create a new DHCP server and allocate a new range to it, and allow both to work in redundant parallel for a while. Then you gradually reduce the range available to the original server so that clients transition off it onto the new one - eventually all of them, and then you can decommission the old server and increase the address space available to the new one.

 

You have to do this over a period of several (my rule is 20) N, where N is your lease time. If you just pull the carpet out from under one server, you leave clients thinking they have leases while in fact the new server is allocating the same addresses to someone else, and you get ugly collisions.

[powdarrmonkey]

You could just use the 1 DHCP server until you switch the old one off at which point you'd just need to ensure that all reservations/exclusions are in place and then just switch off the old and authorise the new one - when clients next need to get an IP address they'll get assigned an address from the new server. As long as the old DHCP server gives out both DNS servers to clients you should be fine.

 

And during the transition, duplicate addresses will be allocated. This is an unsafe approach.