Airport Extreme with Comcast Arris TM502G. Cannot connect to internet

Hope someone can help.
I'm trying to set up an Airport Extreme with my iMac and am apparently having issues with the Comcast Arris TM502G.
Symptoms are:
1. When iMac is connected directly to Arris TM502 modem via an Ethernet cable, I have an internet connection.
2. When iMac is connected to the Airport Extreme via an Ethernet cable, which is then in-turn connected to the Arris Modem, I have no internet connection even though the Ethernet  port lights for both the connections are green.
3. The link light on the Arris modem blinks the same whether I have it connected to the iMac directly or through the Airport Extreme.

After searching Google, I've discovered there are quite few threads from people having the same issue, however, nobody seems to have a solution.  So here I am.

Heres the summary of the Airport Base Station:

Airport Tab:
Base Station Status: Internet Connection (Amber)
Version: 7.2.1
Serial Number: 6F70537TVZC
Airport ID: 00:19:E3:33:12:98
Ethernet ID: 00:16:CB:C1:87:54

Wireless Mode:  Create a wireless network

Connect Using: Ethernet
IP Address:

Internet Tab:
Connect Using: Ethernet
Configure IPv4: Using DHCP
IP Address:
Subnet Mask:
Router Address:  This field is blank
Ethernet WAN Port: Automatic
Connection Sharing: share a public IP address

Hoping someone has a solution.  So far, Ive tried resetting the modem, re-powering the modem, resetting the Airport Extreme.

It appears the modem and Airport can see each other, they just arent communicating in a way that will allow me to connect to the internet.

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Dumb question, but did you make sure you are connecting the WAN port of the Airport to the modem?
One thing to try. Power down the modem for 5 minutes. Power down the Airport Extreme. Connect the Airport Extreme to the modem. Power up the modem. Wait for the lights on the modem to stabliize. Power up the Airport Extreme.

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By the way, the 196 IP address the Airport is showing is a self-assigned address, meaning it is not obtaining and IP address from the modem by DHCP. One possibllity is that you have connected the modem to a LAN port of the Airport rather than to the WAN port.

 Another possibility is that modem has "memorized" the machine address of the Mac and won't let another device connect. Many routers allow you to do "MAC address cloning" to get around this, but the AEBS does not supporrt MAC address cloning. Sometime cycling the power to the modem will cause it to "forget" the machine (MAC) address of the Mac and allow a new device to connect.
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