Moving RAS to new domain

We have created a new domain and are migrating our old servers & machines to it. I have encountered a problem with moving the RAS servers though, when I join them to the new domain they are issued with the new IP addresses etc, but when users dial in they are still issued addresses from the old IP range.

This is confusing as we have a router between the domains and use DHCP for IP allocation on both the domain and the RAS.

Any help would be appreciated.