DHCP an NAT

[Nathan Burgener]

Hello

I have 2 networks, which are connected over a VPN. In the network A,  
there is a DHCP server.
In network B I have the client. But all client address from source  
192.168.3.x get a IP from network 172.18.1.x with NAT and then the  
traffic goes through the VPN tunnel.
On the router in network B I have an ip helper-address to the DHCP  
server.

Now the server gets the Discover from the client with the following  
informations:
Source IP 172.168.1.1
Destination: Address from DHCP server
Relay Agent IP Address: 192.168.3.1

The DHCP server will now send back the offer. But the servers sends it  
to 192.168.3.1 and not to the address 172.168.1.1
How can I change that?

Yours sincerely