this post was submitted on 18 Apr 2024
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Home Networking
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So if the switch does all of that, what does the router do?
Switches (particularly layer-3 switches) have basic routing capabilities to connect different VLANs, but that is not their focus. Their purpose is to facilitate communication between devices connected to the same subnet, and across subnets on the same LAN.
Routers specialize in communication between networks, e.g. between a LAN and the internet. They can use static routes or dynamic routnig ~~algorithms~~ protocols (e.g. RIP, EIGRP, OSPF, BGP) to find the shortest route, often across many routers, from the source to the destination.
Think of routers as intercity railway lines, and switches as local transportation.
The device that is usually referred to as a "home router" is usually a combination of a router, a switch, a wireless access point, optionally a cable modem, and sometimes a telephone modem; plus it offers services like a firewall, NAT, and sometimes VPNs. It does everything, but with a much lower performance compared to dedicated hardware.
Can I come and live with you so you can break everything down to me so simply 😂
Okay, so for my network, I would set my existing router to modem mode and then have that plugged into the router and then the router plugged to a switch, a switch connected to an access point and my devices connected to the access point. Does that make the modem the Eurostar? In that case, what is the router even doing? Does that mean I would need an access point for each VLAN? And if it does, is it really virtual if it's tied to physical hardware.
Generally, yes. WAN -> modem -> router -> switch -> (devices, wireless AP, other switches).
If you set the internet provider's device to modem/bridge mode, it will do one thing, and one thing only: forward traffic between the ISP's infrastructure (like DOCSIS, telephone line, PPPoE, FrameRelay, etc) and an Ethernet port. The traffic on that port will be unfiltered and dangerous internet traffic.
The first device after the modem should be something with a firewall and NAT. In most cases, this is a consumer-grade router, but it could also be a computer running pfSense/OPNsense/OpenWRT (which basically turns it into a router). The firewall's role should be obvious -- it filters everything that passes through it, and only allows permitted traffic.
NAT (Network Address Translation) is a bit more complex. I'll skim over the details -- it allows you to have a private network of any size communicate with a public network using only a single public IP address (which is usually supplied by the ISP). It also enhances security because NAT is what facilitates port-forwarding, and your private network won't be exposed through the public address unless you do that. NAT is almost always handled by the router. Firewalls can be integrated into the router, integrated into the modem, or implemented as a discrete device -- make sure that the internet traffic passes through at least one firewall!
The router in this case handles NAT, finding the first hop on the internet for outgoing traffic, and routing incoming traffic to the subnet that contains the destination device.
From the perspective of packet switching on the network, a wireless access point is really no different than a switch, except it facilitates communication with wireless devices. Depending on the model, APs can support VLANs, and each wireless network can be assigned to a different VLAN on the same device.
For example:
This way you can set up the router to allow both subnets to communicate with the internet, the family subnet to talk to devices on the guest subnet, but prevent guest devices from talking to the family subnet.
How you achieve this depends on your ISP and what devices you own. For example, the ISP might only give you an IPv6 address, which is an altogether different headache.
Thank you so much! I kinda had the bits in my head, but you've connected the dots for me. I am truly grateful!