Let's say you are lucky enough to have 2 or even 3 connection to the Internet, it would be a great idea to have a virtual IP as default gateway for the network. If you're already familiar with HSRP/VRRP that's exactly what I mean. The idea is to track the WAN interface and Internet availability on the individual devices. These devices participate in the vIP election. Every device has a priority, you should know the rest of the story... An alternative without using additional software would be to look into ICMP redirect. It could be a nice helpful addition to tomato!