When I did this on my Linksys here (more sophisticated router), I disabled NAT (set to router mode, not gateway mode) , and allowed traffic all traffic from the WAN port. Have you done this?
If you don't disable NAT, your DC server will see lots of connections from the same IP address, which is not ideal.
I was going to say the same thing, just different

Your Linksys is technically an "Internet gateway" in that it does NAT, firewall, and routing all in one box. You need to make it only do routing, if possible.
When you do that though, the server will no longer be able to communicate with your 192.168.2.x clients because it doesn't know how to route traffic there. The Linksys in it's default mode makes traffic "look" like it is coming from an IP on the 192.168.1.x network, so the server knows where to send it's responses to. Once you shut off NAT though, it's a whole different ballgame.
You can either create an internal route in the router whose IP is specified in the servers' Local Area Connection, OR, go to the command line of the server and issue the command:
route add 192.168.2.0 mask 255.255.255.0 <ip address of Linksys router> -p
This allows the server to route traffic to the 192.168.2.x clients by sending that traffic to the IP address of the Linksys router that connects the 192.168.1.x network to the 2.x network. The "-p" makes the route persistent, so that it survives reboots.
If the route needs to be removed later, do "route delete 192.168.2.0".
Normally, I would use a more robust router such as a Mikrotik or at least a Linksys WRT-54gl that is upgraded to DD-WRT (I sell these on eBay if you are interested

)
Eric