I guess my real question here is:

Does enabling "XBox LIVE Open NAT" increase the risk of attack for other devices on my local LAN?

(The setting is found under Security--> Smart Defence --> Games --> Xbox LIVE)

The microsoft website:

http://support.microsoft.com/kb/908874/

Implies that allowing the listed ports:

TCP 80
UDP 88
UDP 3074
TCP 3074
UDP 53
TCP 53

Should get the XBOX live working, but if I leave XBOX live/OPEN NAT disabled and add rules to allow communication between XBOX and WAN / WAN and XBOX on those ports the XBOX-Live still does not work.

Other readings imply that fully UPNP support is required.

Any suggestions/input appreciated!

The Open NAT option was added so that XBOX will work.
I am not familiar with any other option to make it work.

Thanks Ido!

Do you have any idea what enabling that option actually DOES to the router's configuration?

Jim

It is implicitly creating NAT rules to allow the XBOX traffic to pass through correctly.

THANKS for the great support!

Jim