I am changing an IP scheme for a customer at their main site. Their branches will be changed to DHCP in the future, but right now I need to change the IP on the DNS server because the IP scheme at the main site has changed.
How can I use the Cisco routers at the branches to redirect DNS requests to the new IP until I get them changed to DHCP? I looked at NAT options and see that I might have issues with the routing and NAT order. Is NAT the way to go with this and if so, do I need to worry about routing and the old subnet being removed at the main site?
You can use NAT for this altho you would need to test as NAT can sometimes "break" certain things.
So lets say you have this setup
HQ DNS server (10.6.1.2) -> HQ R1 (192.168.5.1) -> (192.168.5.2 - int s0/0) BRANCH R2 (int fa0/0 -10.5.1.1) -> client PC
where the link between HQ R1 and BRANCH R2 is the WAN link.
You want to present the DNS server to the client as 10.7.1.2 even though it's real address is 10.6.1.2.
ip nat inside
ip nat outside
ip nat outside source static 10.6.1.2 10.7.1.2
ip route 10.7.1.2 255.255.255.255 192.168.5.1
You need the route because the router performs routing before NAT on the inside to outside interfaces so you have to make sure any requests for 10.7.1.2 are routed to the interface that has "ip nat outside" configured on it.