Unable to obtain IP address from WNDR4300v2 after setting as access point

I have to admit, this is my first time trying to extend my wireless range, and I'm confused by the whole access point concept. It seems like what I really want is  a repeater, but that mode isn't available on the 4300v2.

I have two 4300v2 units. One is set as a normal wifi router. I want to setup a second 4300v2 to extend the range of this "base" router. Ideally, I want the wifi SSID and passcode to be the same between the two wifi units. So the wireless client can move seamlessly between the two without having to make new connections.

When I follow the instructions to set the second unit as an Access Point, it gets assigned an IP from the original router as 10.0.0.1. I then take the access point and move it away from the original router. Just within wireless range of the original router. I don't connect anything to the WAN port of the AP. My wifi client has good signal from the AP, but is unable to obtain an IP address.

What am I doing wrong?

Thanks!