What mode/setup for connecting with 4G router

Hi all!

I have a Linksys in PPPoE mode and the ISPs router in bridge mode. In this way I connect cable and wireless devices to the internet.
Soon I am moving to a new home where there is no cable for internet, I have to get a data sim and a 4G router.
Because I don't want to lose my Linksys neither the OpenWrt, how to connect the Linksys with the 4G router, in which mode;
PS. I have 2-3 rj45 devices and 2-3 wireless devices

Thank you team

The way that you will connect all depends on the 4G modem that you get and what features it has available. If it operates in a bridge mode, you'll likely connect using either DHCP or PPPoE -- depending on the modem+ISP requirements.

If it only operates in router mode and does not offer a bridge mode, that would mean that you will almost certainly connect via DHCP. Assuming that you wish to keep OpenWrt operating in routing mode (vs just as a dumb AP), you'll connect your Linksys WAN to the 4G modem/router's LAN. When you do this, make sure that your OpenWrt LAN subnet does not overlap with the LAN of the 4G modem/router device (if they conflict, routing will not work).

The routers manual says
Operating Modes 3G/4G Router, Wireless Router

What are the benefits of keeping OpenWrt operate in routing mode (vs just as a dumb AP);

I have also 2 smart plugs, so I guess it's one way solution to routing mode

That doesn't really provide sufficient information to know if it offers a bridge mode, but it does seem to imply that it does not. That means that it will most likely operate as a router.

This depends on your use case. If you don't trust the firewall of the 4G modem/router device, you will be best served by using OpenWrt as a router. This means you will be double-NAT'd -- this is not ideal, but it is of little consequence most of the time. If, on the other hand, you are comfortable with that device's firewall, you can just run OpenWrt as a dumb AP which basically just as it sounds -- it is an access point (and ethernet switch) that doesn't do any routing (for reference, when we say "wifi router" -- we're actually talking about 3 devices packed into one: a router, a wifi AP, and often an ethernet switch -- 3 functions integrated together in that device, kind of like a multi-function printer). There is no downside to using OpenWrt as a dumb AP, provided that it fits the need and your existing router has a good firewall and any other ancillary features that you might be using.

I'm not sure why you are equating smart plugs to routing mode. Without more context, my interpretation is there is no reason you'd need your smart plugs behind an OpenWrt router vs the modem/router device (operating as a router).

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