I'm still trying to work out some issues with my router and might be close to being set. I've been posting in the PS3 setup sticky but will give the highlights here so that you can check your router settings and make sure you're getting the best you can from it. NOTE/DISCLAIMER: these are just recommendations and are based on my personal research regarding dropped/blocked network traffic from app's like bit torrents. Just because I'm comfortable with these settings, please use your own judgement before making router changes.
I've been experiencing lag and blocked packets from two new netgear routers: WNR3500L and WNDR4000. I also have seen traffic from my PS3 being flagged as a denial of service attack (DoS: STORM). You see that by surfing into your router and looking at the log. I'm running two game consoles on my LAN so running a DMZ or using port forwarding/triggering is not a possibility as these require turning UPnP off. So one console would work well while the other would suffer. Also note that even with the optimized settings, the PS3 reports NAT Moderate most of the time. I'm ignoring that based on testing/playing MW3.
Important settings for "best" router performance for MW3:
* enable UPnP on the router and in the PS3 network configuration, UPnP settings page.
* set NAT Filtering to Open, WAN setting page. You'll still have NAT operative, but just less restrictive. Running firewalls on your PC's is recommended.
* disable SPI (stateful packet inspection) firewall, DoS protection or port scanning, WAN setting page. Different routers call it something different but something like this settings will show up as a check box to disable it. This was the setting causing the throttling on the port and sometimes flagging game play traffic erroneously as a DoS attack.
* make sure you do not have a router behind a router situation. your modem (cable or DSL) should be in bridge mode or equivalent first, if it has a router built in. Not doing so results in 2 layers of NAT which is very bad for on-line gaming. The above 3 fixes will not help you until you address this.
Game play after making the last change (disabling DoS/SPI firewall) was really, really good. It was like a background layer of lag was lifted. I'd be interested in hearing others experiences, after making this change alone.
I hope this helps others get the most out of their router and MW3 online gaming experience.