Since The Dawn Of Time ™ it’s been possible for a networked device to have a default route. Way back then, before our beards turned thick and grey, all routers were called “gateways” so the default route was called a default gateway in those ancient times.
The purpose of the default route is to provide a last ditch option when the device does not know what to do. Basically, whenever a networked device doesn’t know where to send some data, it can do the equivalent of a hail mary pass, and just chuck it blindly at a mysterious place where hopefully there will be a router or modem of some sort which is part of the global Internet. This is actually how the vast majority of Internet traffic is handled, believe it or not; PCs, Macs and webservers typically don’t know anything about how to reach other things on the Internet. The router that sits at the end of their default route handles it for them.
The Cisco 2960 is a commodity network switch that has recently been given some routing capabilities by a software update. They are quite commonplace; there’s a couple stacks of them around my job site, hanging off the larger Nexus fabrics.
The 2960 has brought some fresh confusion to the terminology, because for reasons unknown Cisco has provided these three commands:
ip default-gateway (when IP routing is disabled)
ip default-network (when IP routing is enabled)
ip route 0.0.0.0 0.0.0.0 (when load balancing across multiple routes is enabled)
To an experienced networking professional, those are all the same thing. If I say “hey, Melvin, set route zero mask zero on your box to point to the core12 router” it means the same as if I say “Melvin, you dolt, your default gateway needs to be core12” or even “the default net should be core12, Melvin!” So this is a remarkably non-intuitive set of configuration options here.
“So what” you say, with a Cisco router you just use the tab-completion and question-mark help features of the command line to learn what to do, right? Who needs documentation, Cisco rocks. Er, except in the current version of the software there’s no help text at all for ip default-gateway, and you can’t use ip default-network until routing is enabled, and it’ll accept ip routes to 0.0.0.0 without using them as a default. So, not so much. Thankfully Keith Barker has a more helpful post than mine, if you haven’t already figured out what you need from this one.