DHCP Rollout

Hi,

Here is the current situation. I have approximately 300 client PCs
over 10 physical locations. All clients, printers, etc. are setup with
static IP addresses. The static nature of the IP addresses has to
remain but we are looking to introduce DHCP so the address assignment
is server based not client based. We are looking to do this with MAC
address reservations.

This conversion in an of itself is not hard, we were planning on
adding all the reservations into the DHCP server, and set the clients
to DCHP rather than static in a phased rollout. The result would be
the clients have no down time. Now due to a VoIP rollout happening in
the near future we have the added issue of re-subnetting our network
to make everything work properly. For most remote locations this will
not be a problem but in our main location it seems to be an issue.

What we were planning on doing is setting up the DHCP server to be /24
ready while still being /16. We were thinking of doing this by
creating multiple /16 scopes with the reservations split amongst them
as they would be in the new /24 world. Because all the /16 scopes
would have the same subnet mask everything would work as it currently
does. Once we setup the new subnets and vlans in the routers we could
just change each subnet mask in the /16 scopes to the correct /24
subnet and we would be in the new schema.

This thought process looks good but the DHCP server will not let me
create multipule /16 scopes on the same network. The issue is that a
giving PC/USER combination MUST have a known IP address for our core
system to work. Also we do not want open DHCP for security purposes
(not just anyone can get on the network). We are a financial
institution so these things can not be changed.

The 2 step process allows us for first move to DHCP and verify
everything works and then move to the new subnet system and verify
everything works. It would be relatively seamless to the end user.
Given that I cant create the scopes, or change the subnet of existing
scopes like I had planned I'm not sure how to move forward.

Am I just missing something? Can I create multiple scopes on the same
subnet? Can I change the subnet mask of an existing scope? Do you have
any recommendations on how to proceed with limited interruption to the
end-user?

Example:

Current: static 10.1.x.x network

DHCP rollout:
scope 10.1.x.x/16 addresses 10.1.10.x
scope 10.1.x.x/16.addresses 10.1.110.x
scope 10.1.x.x/16 addresses 10.1.20.x
scope 10.1.x.x/16 addresses 10.1.120.x

Subnet rollout:
convert scope 10.1.x.x/16 addresses 10.1.10.x to scope 10.1.10.x/24
convert scope 10.1.x.x/16 addresses 10.1.110.x to scope 10.1.110.x/24
convert scope 10.1.x.x/16 addresses 10.1.20.x to scope 10.1.20.x/24
convert scope 10.1.x.x/16 addresses 10.1.120.x to scope 10.1.120.x/24


Thank you,

Justin Zaun