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I am learning about Networking, and based on what I have learned so far, this is how a LAN network is set up:

enter image description here

So basically all of the computers and the Router are connected to the Switch. If a computer wants to send data to another computer, the data will go through the Switch without reaching the Router, and if a computer wants to use the internet, the data will go through the Switch and reach the Router.

But this is not the way the LAN network is set up in my house! this is how the LAN network is set up in my house:

enter image description here

So all of the computers are connected directly to the Router (without using a Switch). Now I think that in reality this is not the case, and that the Router actually have a Switch built into it, am I correct?

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Yes. If the consumer grade router has several ports it means a switch is build into it.

The first port (sometimes called WAN port) is usually used for the external network (internet), but the rest can be used for your internal network just as a switch.

If you need more ports (or your router only have 1 LAN port) you can attach a switch after it without any trouble.

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    At the OS-level, also, there is a "bridge" configured which connects the Wi-Fi AP (and the occasional USB-Ethernet port) directly to the switch as well. – user1686 Jun 2 '16 at 7:40
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Yes. Where I work we use several old routers as switches. We disable DHCP, set the internal (LAN) IP to a value that won't collide with other devices, set the WiFi, finally we don't use WAN port. Then these devices are cable-connected to the main router which is the only one with DHCP server running.

Some hints:

  • When assigning IP, write it down somewhere. It will be difficult to reconfigure your router if you don't. Reset to defaults is an option -- but what if you need to make a minor change to WiFi setup only? You don't want to set it all from scratch.

  • Assign IP/netmask from within your LAN to make the router HTTP admin interface (if on) available in your network.

  • Assign narrower netmask to make this interface available only to some IPs in your LAN.

  • Assign IP from outside of your LAN to make the device virtually invisible. Then, to communicate with the router, one will have to manually set their computer IP to match the router. Switch on LAN ports (and even bridge with WiFi) should work regardless of IP setting.

The two last hints may be useful if you suspect some of your LAN users will try to bruteforce the router. They will have to guess and set the right IP in their machines in order to reach the router in the first place.

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Multiple, identical LAN ports are generally connected via a switch to a single, internal interface.

However, talking about consumer devices, switches for consumer market most often aren't 'real switches'. For production cost reasons they are some kind of hybrid between switch and hub.

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The short answer to your question is yes.

But the real issue is that you are using the word "router" to mean two different things. In the first case, you are using the word "router" to mean the execution of layer 3 routing functions. In the second case, you are using the word "router" to mean a box that says "router" on it that performs layer 3 routing functions as well as other functions.

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