I currently have an SMCD3GN router through Rogers. I am connecting a Cisco 891 to it, using the SMC as the external WAN.
For examples sake, let's say the internal IP on my SMC is 192.168.150.1. The 891 has an IP connected to the 192.168.150.0 network of 192.168.150.150. The other side of the 891 is 10.10.10.1 (the default for the 891.) Anything connected to the 891 (say a device with an IP of 10.10.10.100) can ping both sides of the 891, and also the internal IP of the SMC. That's it. It can't ping any machines I have on the 192.168.150.0 network, and can't ping anything on the outside (past the SMC.) From a machine on the 192.168.150.0 network I can ping everything, including the 10.10.10.100 machine (due to me putting a static route on the SMC pointing to that network.) If I add a static route to my 192.168.150.101 machine, the 10.10.10.100 machine can now ping that machine also, but nothing else.
Is there a way to set up the SMCD3GN to allow me access from the 891 and it's corrosponding network to the outside, and the rest of my 192.168.150.0 network?
I called Rogers and asked if I could get a secondary IP (which would make my life a lot easier with this!) and I was told that wasn't offered anymore. 
I would put the SMCD3GN in gateway mode and add another router between the 891 and the SMC, but that's just not feasable at the moment with the way things are set up here (have to deal with family in the house that also uses the internet!)
If anybody has any ideas, please let me know! Thanks!