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My network skills are a bit limited but I would like to extend a current network (network 1) the following way:

network

Currently I have a "network 1" with subnet 10.0.0.1/24 with DSL (and active DHCP that can't be turned off), a bridged router and some devices. However this network is not always powered on.

Now I additionally got a LTE-Router (with it's own DHCP and VPN capability) and want to use it so that device 1 is always connected to the internet (in network 2 with subnet 192.168.0.1/24). However, currently I only have a very limited LTE data plan so I just want device 1 to be connected to the LTE internet and the rest should use the DSL internet if it is available (maybe sometime in the future I will completely switch to LTE).

If I connect from outside to the VPN of the LTE-Router I want to access all devices in the 192.168.0.1/24 subnet (for e.g. device 2).

Connected to the managed switch there will also be an access point which provides WiFi (the internet should be used from the DSL-router).

Both subnets should be reachable from each other (for e.g. device 2 can reach device 5 and reverse).

Therefore I thought about putting a router (the "magic routing device" in the picture) between network 1 and network 2 (like a router cascade) and maybe add a static route for it so both networks can reach each other.

In the access point I would then add a static IP (with the gateway from the DSL-Router) so the internet there is provided from network 1.

I am not sure if this would work and if a normal consumer router is enough for this or I would need for e.g. a Mikrotik hEX or something.

Can someone with a bit more network experience say if this can be done easily?

2 Answers 2

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That "magic routing device" is a router.

Your static routes wouldn't be added on this device itself, however. (As it is already a direct member of both networks, it doesn't need any custom routes to them.) Instead, each network's current "default gateway" needs a static route for the opposite network, via the intermediate router.

That is, the "LTE-Router" would need a static route for 10.0.0.0/24 via 192.168.0.x, and the "DSL-Router" would similarly need a route for 192.168.0.0/24 via 10.0.0.y, where both "via"s are different interfaces of the same magic routing device.

If either of those routers doesn't support defining custom static routes, you'll need other tricks such as having the intermediate device do proxy-ARP. (That would be easier if the two networks were numbered adjacent.)

I am not sure if this would work and if a normal consumer router is enough for this or I would need for e.g. a Mikrotik hEX or something.

In theory, that's literally the main job of a router. Any router should be able to connect two IP networks, because that's what a router does.

But in practice, most consumer routers come with an OS that's really built around the idea of connecting a LAN specifically to Internet, and their settings panels will often just not allow you to do anything else, e.g. they might enforce NAT usage, things like that. Indeed a lot of them won't even allow you to define custom static routes. (Though of course there are some more flexible firmwares like OpenWRT.)

So it's often much easier to get a router which already provides the flexibility out of the box, such as hEX or an ER-X.

(You wouldn't even need to ad that intermediate router if at least one of your existing routers supported creating a 3rd network, basically "LAN2", and dedicating one of its ethernet ports to it. But again that's something most consumer routers just won't let you do through their OS.)

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should work with any router between.

You only need to be able to tell the both existing routers to tell their DHCP-clients the route to the other network. If not possible you've to tell it each client direct to make it working.

like

route add -net 10.0.0.1/24 gw <THE IP OF YOUR NEW ROUTER IN THIS RANGE>

in the Gateway of your Network 1 and the

route add -net 192.168.0.1/24 gw <THE IP OF YOUR NEW ROUTER IN THE SECOND RANGE>

If you've got a device that has allready to network connectors you may not need a new router and only tell this client to be in both networks and accept forwarding and maybe masquerading. What will do the job of the router allready. Some router has got the ability to use two networks allready and maybe one of yours is able to support at one connector a second network. But there for I would need more information about the devices and don't know if I am able to find time to read their functions out if I don't know them.

On a real router you may have to switch of the firewall because it may filter the incoming traffic from wan site.

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