Connect 2 routers in the same subnet

[ali232]

Hello.

I have two AX86U routers (R1 and R2). Both have it’s own WAN connection (WAN1 and WAN2). There are some devices connected to each routers. I’d like to reach devices connected to R1 from devices connected to R2 and and vice versa.

If I connect the routers LAN port and place them in the same subnet it can work?

Thanks for your help.

 

[eibgrad]

Problem is, you then can't control which DHCP server is controlling assignments to which devices, so it just becomes a roll of the dice which WAN is used by which device. Those routers also have to be configured to NOT overlap their IP assignments.

The better way is to keep them on separate IP networks, but place a third router between them, thus preventing the above problem. You then simply route between the two IP networks.

This can also be done using VLANs, without having to introduce another physical router. But unfortunately ASUS doesn't support VLANS natively for such purposes. You'd have to use the CLI.

 

[ColinTaylor]

If I connect the routers LAN port and place them in the same subnet it can work?

You would have to turn off DHCP on one of the routers and manually assign its LAN port with a non-conflicting IP address. But then all of your LAN DHCP clients would only be using one of the routers as their default gateway to the internet. So it would seem to be a fairly pointless exercise.

 

[eibgrad]

P.S. I'm assuming here that each WAN has its own ISP, so you want/need to preserve those connections. If NOT, if just one of them is connected to an ISP, you could obviously daisy-chain the other to the one connected to the ISP, WAN to LAN. Then using some firewall rules and static routing allow access from the upstream router to the downstream router. But again, I'm assuming that's NOT the situation.

 

[bbunge]

Are the routers in the same building and connected to the same modem/ONT? Maybe WAN Aggregation and AiMesh could be used?

 

[eibgrad]

BTW, another option would be to use a routed (TUN) site-to-site tunnel w/ OpenVPN, or bridged (TAP) tunnel. The latter assumes different IP networks, while the latter the same IP network.

Granted, it's NOT nearly as efficient as having direct local access, but in some cases, it gets around sticky problems. For example, using a bridged (TAP) tunnel, you simply block DHCP across the tunnel to keep the two sides isolated from each other for those purposes.

In both cases, you avoid the need for a third router or VLANs support.

I'm NOT suggesting either approach is ideal, but different users may have different solutions they consider viable depending on available hardware, budget, etc. So it's hard to pin down exactly what will work best w/ so little details from the OP.

 

[dosborne]

Back to the the OP, it is entirely "doable" and makes sense in a lot of cases. As an example, I kept an older dsl link active as a backup plan in case my primary ISP was unreliable. As pointed out, you only want 1 DHCP server active, but then you can manually configure specific devices to use either your r1 or r2 as their default gateway. That's pretty much all there is to it as a basic configuration. Link aggregation, automatic failover etc, are possible too but not necessary depending on your actual usecase.