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Typically with personal WiFi, you have your ISP line into the home which connects to a modem, then a router (or hybrid of both). Then the router produces a network.

But now let's say you take an Ethernet cable form the first router (we'll call this network A) and connect it to a new router (we'll call this network B). Instead of extending the network, you use it to setup an entirely new WiFi network.

Setup shown here: Sub-Network Setup

So my question[s] is...

  1. Does Network B act as sort of a sub-network or is it independent as if it were getting a line directly to the ISP?
  2. For network security, do the settings of one network depend on the other? Ex) IF I want to port forward a device on Network B, would I also have to do it on Network A or would just the once be enough?
  3. Are there any inherent limitations of this setup?
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    You are missing one question: (4) Is it a good idea to do it that way? A: No. It's an easy setup for people with consumer-grade routers, and it will work (mostly), but for anyone who's seen a proper network with subnetworks, it's a really, really horrible way to do things (starting with the double NAT). The downside of a proper network setup is that it's quite difficult to realize with the default firmware on consumer-grade routers, so most home users do end up with something like in your diagram.
    – dirkt
    Commented Sep 13, 2018 at 10:45

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If you're using the router's regular setup (NAT) and connecting a LAN port on router A to the WAN port of router B, then everything on the second network B will apparently have (share) router B's "external" IP address. Any rules that the main router (A) has for router B will apply to everything connected to router B.

If you wanted to connect from network A to a specific device on B's network, you'd have to set up port forwarding on router B to that device. If you wanted to connect from the internet, you'd need port forwarding on router A to router B, then from router B to the specific B device.

Similarly, outgoing connections from a device in B's network that needed a special setting on router B would need a similar setting on router A too.

That's the basic limitation, and why setting up something different, like a bridged network, is a good alternative to avoid these hassles.

But as described, a device in B's network should have perfectly fine access to the internet. It (the second router) could even be considered as an extra layer of security for B network devices...

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If you connect the LAN port of Router B to the LAN port of Router A, then Router B becomes the switch.

Then network B can not be said to be independent or a subnet. You can think of this as a client of Network A. The security of network B depends on the security of network A. As for the limitations, there is no in this setting.

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  • So basically you're saying if you use the Ethernet ports that it will just be a switch, but if you connect via wifi it will then be subject to router B's network and router A's network?
    – CTOverton
    Commented Sep 15, 2018 at 21:34

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