I posted a thread the other day about problems I was having with the XBox Live Party Chat system and my Vigor router. After more investigation than an end user should ever have to do, I discovered that the problem was down to routing.

I've got a dynamic IP from VirginMedia and a static IP from O2.
I use my VM as my primary connection (and default gateway). O2 is WAN2 and back up.
I use a Load-Balancing feature of the Vigor to force all of my XBox traffic onto WAN1.

The problem I have is that several of my friends also use BE and O2 as their ISPs. This means that all of us have public IPs in the 78.105.x.x subnet. I'm 78.105.120.x whilst a friend (on BE) is 78.105.127.x The subnet mask I was given to use with my IP is 255.255.248.0. Therefore the Vigor is routing all traffic destined to the 78.105.x.x network out via WAN2, ignoring my Load-Balancing rule and this is breaking XBox Live (to those people on O2/Be).

To fix the problem I've made my o2 subnet more restrictive (255.255.255.0). The thing is, I'm not sure what impact that might have on other things ? 

I would set the WAN interface's to only turn on WAN2 upon failure, don't try to use load balancing.

I'd love to do that but I work from home and VPN into the office during the day.

My secondary WAN provides an "unlimited" connection whose download speed very closely matches the remote office's upload. For that reason all VPN traffic routes over WAN2. The traffic limit on VM is soo lame that I can easily end up reducing my 50mb connection to 10mb through the course of a day just because of VPN traffic