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Issue #708: February 14-20, 2021

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Q: I have a mesh Wi-Fi system (Amplifi) set up in my home. The router has a wired connection to my ISPs modem. My computer also has a wired connection to the modem. Recently I bought a new printer and set up wireless printing with my computer. Unfortunately, when the computer is using the wired network connection it will not communicate with the printer even if the computer is also connected to the wireless network. In order to print, I must disconnect the wired connection between the router and the computer. If this isn’t annoying enough, as soon as I disconnect the wired connection to the computer, the router loses its internet connection even though it is still connected to the modem. I can always set up a wired connection between the printer and the computer, however my issue is that the router loses its internet connection when I disconnect the computer from the modem. I do not understand why this would happen, the router is still connected to the modem and nothing else has changed. I have tried checking the ethernet cables and the connections to see if perhaps there is something loose, but that doesn’t seem to be the problem. By the way, I enjoy your column and often check your website.

– Kathryn M.
Defuniak Springs, Florida

A:  I just happen to own an Amplifi mesh system too, Kathryn; probably the same one as yours.  For those of you who don’t savvy the term, a mesh system is a type of Wi-Fi device that consists of a centrally located router/switch that connects to your modem, but with multiple, additional, devices called mesh points that connect wirelessly to the main device, and act as repeaters.  The mesh points can be strategically placed around your home to extend your Wi-Fi pool and provide greater coverage than you would otherwise get from a single device.  It’s like having multiple Wi-Fi access points, except in a mesh system, all the access points share the same Service Set Identifier (SSID) and password, which makes moving between them seamless from the user’s perspective.  In almost every case, the device with the strongest signal is automatically selected.

Now then, as I see it Kathryn, your main issue is that you’re presuming that because your hardware is all connected together, that you have a single home network.  The reality is that you have two completely different networks, with your computer connected to one, and the printer connected to the other. In this configuration, they can neither see nor talk to each other.

The defining characteristic of a network is that it has a single gateway through which all traffic is funneled to get to the next level of connectivity.  The ISP device is a gateway, but your Amplifi device is also a gateway.  Connecting them together is fine, and is actually necessary for your Amplifi device to be on the Internet.  However, trying to make devices connected to one network talk to devices on the other network can be challenging.

Your ISP’s modem has a router and switch built-into it.  I know this to be true, since it apparently has more than one RJ-45 jack on the back for connecting Ethernet cables.  If the device was purely a modem, it would have only a single jack, which is where you would connect your separate router.  Both your Amplifi router and the ISP’s device also will have a Dynamic Host Configuration Protocol (DHCP) server running, which is what generates local IP addresses when devices connect.  On a typical home system, these addresses are in the range of 192.168.1.xxx.  But you have two DHCP servers running on two different networks, generating IP addresses in the same range.  It is the gateways that makes this possible, and is the same basic thing that allows everybody on the Internet to use the same IP address range without stepping all over one another.

Setting up the routing that’s necessary to make devices on your two different networks talk to each other is beyond the capability of your average home network user, and I’m not even going to try and cover that advanced topic here.  It would be far easier for you to just put your devices on the same network.  Your Amplifi device is designed for exactly this purpose, and so has multiple RJ-45 ports on the back.  All the devices on your home network should be connected to these.  The only device that should be connected to your ISP’s device is the Amplifi router itself.

As for your Amplifi seeming to disconnect from the Internet, I think that’s a combination of the way your ISP has your modem programmed, and your computer being connected to the wrong device.  I suggest that you power everything off for at least 1 minute.  Then connect them correctly, which is Amplifi to the modem, and computer to the Amplifi, then power them on one at a time, modem first, then Amplifi, then computer.

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2 Responses to “Issue #708: February 14-20, 2021”

  • kmcmackin says:

    Thank you for answering my question. Through trial and error I eventually got everything working but had no idea why connecting the computer to the Amplifi device instead of the router would work. I honestly thought that since I had turned off the router function on the ISP’s device that I only had one network. Everything is working fine now.

    • The Geek says:

      Glad to hear you’re working again! I imagine you didn’t actually turn off the ROUTER function in the ISP’s device, but rather the Wi-Fi. Can I guess that you’re a Cox Communications customer? Because I have that exact setup at the Geek House.


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