For all intents and purposes, “gateway” just means “router,” especially in consumer/home networking. Routers act as a gateway, routing traffic from one network to another network. On one end of the router is your WAN (ISP / internet at large / etc.), and on the other end if your LAN.

Switches on the other hand are “dumb” and only act to expand a network. They basically act like a power strip does: What was one port is now more. (This example will probably upset someone for reasons, but they’ll also understand that it works well enough.)

Thought exercise: What happens if you plug the WAN cable from your ISP into a dumb switch (like https://www.amazon.com/dp/B00A128S24), and from there you plug in several devices (PC, printer, etc)? I am not answering that question because just about anything can actually happen. It depends on how your ISP is configured and will almost certainly not work 100% correctly.

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Now onto the actual response: For the most part, every consumer router is a router/switch/wifi AP combo box, and are capable of being used for all or any combination of those features.

If you’re not planning to use your device as a router, then we’ll ignore the routing functionality. All prior points where I say “this happens at the router, not the switch” still apply. (Your device can still be called a router, as that’s what it’s sold as, but you’d be using it with the all routing functionality disabled, only using the switch and possible WiFi features)

If you do plan to use your device as a router, then the prior points where I say that now apply.

Anyway, you’re in luck since the switch built into your device is almost certainly VLAN-capable (it’s quite rare, but some devices are not capable of it). If you’re not using the device as a router, that’s where things probably end, since (at the switch level) VLAN support is pretty much the only thing of note.

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I spent so long writing this I actually forgot what I was trying to say initially. I’ll likely draw a diagram to explain some things for you.

The important thing is that “switches” (or your device if you’re not using the routing functionality) are “dumb devices” that only do very simple tasks and generally aren’t capable of much in terms of advanced security features. “Routers” are smarter devices where the task they do is a bit more complex, and are where the advanced security features can actually be applied.