When I was back at home Christmas, I played Xbox Live over at Ork's place and was blown away by the gameplay. I was also blown away by just about everyone else in the game. 
I vowed right then and there that when our ADSL 1544 came back up, I was going to use the 2-month free trial and sign up to play.
Since our ADSL came up last Wednesday, I decided to give it a try. First I tried using my Linksys WAP54 as an AP Client on my wireless network. I was able to get only so far into the sign-up phase before getting “Xbox Live Not Responding” and after three tries “Cannot connect due to technical difficulties. :-$ Please try again later” I went through some troubleshooting and diagnostics and found that your router needs to have it's MTU set to 1365 or greater. My router was set at 1500, so that should be fine. I was able to ping the server, and my latency was anywhere from 300-600ms. On the testing page everything configured and connected properly, but I got no joy. I also tried by draping a cat5 wire across the entire apartment and got the same problems.
Late Thursday night I tried again, and this time I ran a packet sniffer while it was working and saw that it was sending a lot of SDDP packets. I had to look that up and found that SDDP stood for Simple Device Discovery Protocol and was part of uPnP. I was flummoxed, as all my settings were OK and my router, a Linksys WRT54G was on the list of compatible hardware on xbox.com. I gave up for the night and as I was doing so, remembered that I wasn't actually using the WRT54G as a router, I was using my DSL modem as the gateway, and it WASNT on the list, and was not uPnP compatible.
I talked it over with the rest of my dept at work the next day, because even though I re-configured my network to “double-NAT” with the Linksys as the gateway for the whole network, and connected to the DSL modem as another gateway, I was still having problems with the DSL modem stopping the packets to and from xbox live.
A few years ago when we first got ADSL down here, the SpeedTouch Pro modem was selling for KYD$500, an absolutely INSANE amount of money. I refused to pay it and spent a week researching alternatives that were compatible with the Alcatel chipset. I found one, eventually, the Efficient Networks SpeedStream 5660 (Link is to Google, Efficient sold off their SpeedStream division to Siemens and they've since discontinued it. There are still support pages, but no product page). It was a one-port ADSL modem/NAT/Firewall/etc which was fine because I planned to plug that one port into a Wireless access point/router anyway, and it's configuration page was way easier than the SpeedTouch and it's Nat pinholing actually worked fairly well (the SpeedTouch claimed to work but I could never get it to). It worked well up until this point: it wasn't uPnP compatible, and I couldn't specify an internal address as a DMZ. I looked for a firmware update that would allow a DMZ or uPnP compatibility but there was no such animal. Same went for the Alcatel SpeedTouch Pro. Damn.
I even went so far as to look up the specs on the current crop of modems that Cable & Wireless was offering, the Netopia 3300 series. I spent the better part of an hour reading specs and datasheets and came to the conclusion that it wouldn't work, either. I was going to go and buy a new modem if that's what it took to make it work! Sadly none of the options had uPnP or DMZ features.
I was down to my last hope: there's a command available at the command line of the SpeedTouch Pro called DEFSERVER. You can specify NAT DEFSERVER ADDR=x.x.x.x inside your network and it will forward ALL packets to that host. In effect, a DMZ. Everton at work suggested that at the beginning, but I hesitated to do it because I believed that anything plugged into the switch ports of the SpeedTouch would be 'outside' the network and unable to reach the DHCP or NAT server. This proved true later on. I unplugged the SpeedStream modem, plugged in the SpeedTouch Pro and changed the wire over to the WAN port on the Linksys.
I went downstairs, fired up Xbox Live and there was NO lag between screens this time and I blipped RIGHT THROUGH to the sign-up page. It worked! :-O I set up my account with my GamerTag and then logged off and tried to get an IP address on Seb's laptop that was jacked into the SpeedTouch Pro. As expected, it didn't work. It would grab a 10.0.0.x/8 address from the SpeedTouch Pro, but it wouldnt be routed anywhere. I downed the network and swapped the SpeedTouch pro upstairs for a Linksys BEFSR41 Cable/DSL router which I had been using for a switch. It was on the inside of the network and therefore was able to pull a 192.168.1.x/24 address and all the rest. We then plugged in the ethernet cable that runs underground to the other apartment building and lit them up, too.
WEP encryption is turned on now, too. Im using Linksys WAP54s as repeaters, and WPA isn't supported when you're using repeaters (yet... according to Linksys) The signal is Excellent in our apartment (duh) and Good next door where Ryan is connecting wirelessly. The next neighbour over gets a LOW signal, but that's penetrating two cinder block walls. I'm going to put another WAP54 in their apartment to extend the range of the network down to the end of the building where Sue is. I'm going to try to get one of those Linksys WES54g “Range Extenders” but if they dont have any in stock, then I'll just configure a WAP54 as a repeater. Im also toying with the idea of putting a couple higher gain rubber duckie antennas on the repeater in the middle of the building to increase the range slightly. Linksys makes these that are branded and have the right connectors, but there are other, un-branded ones (Click here for Fleeman, Andersen & Bird's website and click on Cisco & Linksys) out there for 1/3 of the cost.
During all this, I also sat down and gave Seb a “Networking 101” which actually was more like a “Networking 330” by the time we were done. We got as far as IP addressing and subnetting, but when I got to sockets/ports he called a time-out and said that was all he could absorb at the time. :) It was good practice for me though.
Before I knew it, it was 6:00 and I made some dinner and we played Halo2 on Xbox live until about midnight.