If you've run across this page, chances are you're looking for a way to set the default gateway on a Cisco SG300 family switch. When the switch is in layer 2 (L2) mode, it's a piece of cake. Administration -> Interface and there it is, right in front of you. (Basically...)

When the switch is set to Layer 3 (L3) however, the entire Administrative Interface option disappears completely and moves down to the IP Configuration section. That's because L3 deals with IPs, L2 deals with MACs, each port / vlan can have it's own IP yadda yadda and technically, you don't need a default gateway on a L3 device, but when you do... Point is, there is no clear Las Vegas lights flashing, in your face, obvious sign for where to add a Default Gateway. If you're a networking guru used to Ciscos catalyst switches, it's probably a no-brainer, but for the small business piddly folks like me, I was clueless. I won't go into detail as to why I needed a default gateway because 99% of people who have these switches, probably won't ever need to set a default gateway, but just in case you do, it's quite simple: "Set it in the IP Configuration -> IPv4 Routes section".