Bridge mode

Hey folks. want make sure i understand this correctly, b/c quite honselty this seems odd design-wise.

I have a singel static IP.  My thoughts were that i put the Cisco GW in bridge mode, assign the static IP to the external interface of my own FW, and i'm done.  This didnt seem to work. i as getting public IPs in the 75.x.x.x range assigned to any device i plugged into the Cisco GW.

Here's what i want:    Internet ---<>Comcast Cisco GW<>--ASA5505<>--Rest of my network.  Really want the Comcast GW to function as a cable modem, and would like my static IP and all my logice running on my ASA5505.

To get the above to work, am i hearing that i need to put the Cisco GW in route mode, but turn off all firewalling, etc? 

But then i'd need the outside int of my ASA to be an RFC1918 address?

THanks

thanks Cekim for sharing the info.  This will definitely given me enough information to setup what i need...although I'm still pretty perplexed by Comcasts use of bridging 😉

All I really wanted was a dumb cable modem and the abiliyt to put a static IP(the one they gave me) on the outside of my ASA. 🙂

thanks again for the help.