I had a somewhat similar problem/experience with adding a 3rd party router to my AT&T's modem/router. For an AT&T U-VERSE modem/router it is impossible to shut off the DHCP. (that is just how AT&T like to corner the market), however, you can use the 2nd router (Cisco) as an access point by going to Cisco router configuration and making the LAN IP address in the same scheme as your router or modem. For example:
Router 1: 192.168.1.1
Router 2: (by defualt) 192.168.2.1 ~ Change the ip to 192.168.1.2 or 192.168.1.253/254
P.S. If you have a standalone modem, it is possible to just shut off the DHCP of the first modem and let the Cisco router take over .
I gave the E2500 an IP of 192.168.1.155 (the DHCP range was 2 - 155).
Once I did that, I can;t access the page any more. I wanted to clone the MAC to that of the modem.
Because that is setting it up as an access point. The E2500 is just passing through the information and not routing it. You need to shut off the DHCP on the 1st router