If you have a modem/router combo device, simply plug your gateway eero into the combo device and follow the setup instructions from there. In this case, you also have the option of putting your modem/router combo device into bridge mode, so it'll only act as a modem. For more, see this article.
Configuring a Second Router on a Static Network - dummies The following code does two things. First, it enables routing on the router, which is necessary even to have routing on the two-segment network (this is not a default setting; you must instruct a router to route when there is more than one interface). Second, it adds a route to the 192.168.5.0 network segment (see Figure 4-2 for an illustration). Set Up a Wireless Router or Access Point - dummies A wireless router or access point brings convenience because you’re not tethered to a wired connection. Setting up a wireless router or access point depends on the software that comes with the router or access point. Wireless connections are more complicated to set up than wired connections. You’re basically setting up a radio transmitter that […] Setting up a second router - December 2017 - Forums - CNET
Connecting a second router to boost WIFI - Verizon Fios
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How To Setup Two or More Routers Together (Port Forwarding
Manually set Router B's IP address to an unused IP within Router A's IP range. For example, you can make it 192.168.1.2. Just make sure you haven't and will not manually use this IP for any other