[SOLVED] Problem with multiple (2) Routers (FritzBoxes) with Internet Connection in the same LAN

Mar 25, 2020
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Hi everyone,

I've been googling and researching this Issue for almost a Year now and I am no closer to a solution, so by now I am pretty frustrated about it.

I live in a pretty rural area so I actually use 2 Internet connections for different purposes (not simultaneous on the same device).

I have a standard landline DSL (Slow transfer speed, decent latency) via a Fritzbox 7490 and a connection via Cable (High transfer speed, horrible latency) via a Fritzbox 6490 Cable.

I have the two Fritzboxes on different subnets. On IPv4 the 7490 on 192.168.5.1 and the 6490 on 192.168.10.1.

I also set up two different subnets for IPv6. (like fd00::xxxx::xxxx::fee3:9ae3 and fd00::yyyy::yyyy::fe84:70e)

The subnets seem to be working, if I adjust my settings accordingly (IP, Gateway, dns,..) the connection works as expected.

The devices I use for example for streaming I have on the 6490 subnet and the device I use for gaming I have on the 7490 subnet.

All devices are connected to the same Switch (TP-Link TL-SG108E).

My Problem right now is that the moment I connect both Fritzboxes to the switch both connections start to experience huge latency spikes (5000 - 10000ms) and sporadic disconnects. The moment I physically disconnect one of the two Fritzboxes everything is back to normal.

I tried different Switches and also reduced my network setup to 1 device + 2 Fritzboxes but I still always experience the same phenomenon.

Is there nothing else I can do than to physically separate the two networks?

By now I'm actually more curious as to why this happens than looking for a solution. I'm thankful for any information I can get.

Thank you :)
 
You are trying to run vlans without the vlans so you can run into trouble. When you connect devices with 2 different subnets to the same switch they are actually all on a single network. All non ip traffic and any broadcast traffic will not be isolated. overlapping networks like you have is rather risky because there really is no isolation.

Since you are not using them at the same time why not put it all on 1 subnet. Just assign say 192.168.1.1 and 192.168.1.2 to the routers. You would just change your default gateway. You can if you really want actually use both by using the route statement and pointing some ip destination to the other internet connection.
 
You are trying to run vlans without the vlans so you can run into trouble. When you connect devices with 2 different subnets to the same switch they are actually all on a single network. All non ip traffic and any broadcast traffic will not be isolated. overlapping networks like you have is rather risky because there really is no isolation.

Since you are not using them at the same time why not put it all on 1 subnet. Just assign say 192.168.1.1 and 192.168.1.2 to the routers. You would just change your default gateway. You can if you really want actually use both by using the route statement and pointing some ip destination to the other internet connection.
 
Mar 25, 2020
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I will try that, thank you.

But is it enough to put the routers on the same IPv4 subnet or would I have to make sure the IPv6 subnets match also (I guess its giving them the same ULA prefix...?) ?
 
I don't remember the last time I had a ISP that supported IPv6. All my experiences with it were pretty bad so I got the habit of automatically disabling it.

Since IPv6 does not use nat you likely still would have to have 2 overlapping networks. Since you would be assigned different IP subnets/blocks from the ISP I can't see any other way.

Just because of the complexity I would likely just disable it.
 

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