[SOLVED] Two ethernet connections not playing nice with each other.

jdlech

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Asus MaximusVIII Hero w/ onboard ethernet (Intel I219-V controller, Driver Ver. 12.13.17.7)

Extra NIC, Realtek PCIe GbE controller, Driver Ver. 9.1.410.2015
Gigabit Ethernet card.
https://www.amazon.com/gp/product/B07KGP342F

On the other end.
Motorola cable modem model #MB7621-10
and
AT&T Arris DSL modem and WiFi router Model #BGW210-700

Windows 10 x64 Home

OK, right now, I have my cable modem connected to my motherboard ethernet, and the connection to the internet is solid. But I've had to disable both controllers on the NIC (rather than pulling the cable). I have the same problem regardless of which NIC port I use. There seems to be some sort of conflict between the two connections that Windows cannot resolve. Once it tries to configure the second ethernet connection, I lose internet in both. It doesn't seem to matter which one I set up first. And the only way to recover is to unplug the ethernet cable from one modem and reset the other one (or disable a controller for one modem, then reset the other modem). Both are set to automatic DHCP. This problem persists regardless of which port I plug which modem into. So I know that both modems and all three ethernet controllers are good. Individually, they all work in any modem/port combination I want. But together, the two connections break each other.

Once we get into manually configuring things, I'm at a complete loss. So please be very specific when telling me what information to plug into each data field and where I can find each field. For instance, let me know if you mean to edit fields in the "internet and settings" page, or through Control panel, or in the Device Manager (properties). They sure don't make it easy to find everything anymore. Also, if you or I need some information, please let me know where to find it.

I sure hope someone can help me get these two connections to play nice with each other.

TIA.
Jdlech
 
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You likely have them on the same subnet.

After you fix that all you need to do is ether remove the default gateway (0.0.0.0) with the ROUTE DELETE command or assign static IP to the interface and leave the gateway blank. I would use the static IP method, you will have to use the delete command everytime you reboot your machine.

This will then send all traffic to your comcast connection except for traffic going to machines on the other subnet inside your house.
 
It will be very hard to do much useful with 2 internet connections.

First the 2 connections must be on different subnet so make sure they both do not use 192.168.0.x for example.

Next and the much larger problem is your machine can only have 1 defualt route/gateway. So even if you change the subnet the PC will select one connection or the other and not use both. You will likely have to use a static ip address on one of the connections and leave the gateway blank so it uses the other connection as the defualt.

So your problems are just beginging after you make that change. Now all traffic only uses the 1 connection. You must manually add routes for the specific IP destinations to tell your PC to use the other connection for those locations. The magic command to do this is ROUTE but it tends to be a rather tedious process so it only works if you have a very small number of sites you want to use the second internet for.

Unless you have a very special need I would not bother with this. What most people think you can do is somehow combine the 2 connections for more speeds, that is not possible unless you are running bit torrent or something strange like that.
 

jdlech

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I guess at this point, I should state my intent.
What I want is to dedicate my comcast connection to my PC, and the DSL to the household. So, my PC does not really need to have DSL internet. However. I still want to be connected to the router because the rest of the household is connected to that router. I want my PC to be a part of the household network, sharing music and movies. So in my case, it's not about speed, but rather connectivity and networking.

So, if I have no internet via the ATT modem, I'll be fine with that... as long as I can "see" all the other computers on the network (via that router).

But as it stands, I have two ethernet connections that are being very rude to each other.
 
You likely have them on the same subnet.

After you fix that all you need to do is ether remove the default gateway (0.0.0.0) with the ROUTE DELETE command or assign static IP to the interface and leave the gateway blank. I would use the static IP method, you will have to use the delete command everytime you reboot your machine.

This will then send all traffic to your comcast connection except for traffic going to machines on the other subnet inside your house.
 

jdlech

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OK, here's where I get all retarded. Exactly how do I check for the same subnet, and exactly how do I fix it if they are the same? I'm afraid you're going to have to hold my hand here. Realize that once I fire up the second connection, my internet will die and I'll have to put everything back together before we can talk again.:oops:
 

jdlech

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You are going to have to do some reading on basic terms it takes too long to explain everything. Look at the IP being assigned to the lan they have to be different. Link 192.168.1.x and 192.168.2.x
OK, here's what I did and here's what I have.
I looked up the IPv4 addy and subnet, then manually entered it for the cable modem. So basically it's the same, but manual (I'm guessing that means "static") now. I left the gateway blank, just as you instructed. I didn't change IPv6 at all. It's still automatic. Obviously, I still have internet through my cable modem.
Then I enabled the controller for the DSL modem and left it on DHCP.

Now the DSL IPv4 connection is intermittent. And so is the internet connection (I don't want to connect to the internet via the DSL modem anyway) The cable modem internet connection is rock solid. But the two WANs cannot see each other. Nor can I access the DSL modems setup page. Meanwhile the IP addy for each is completely different. One starts with a 192 and the other starts with a 68.

The IPv4 subnet mask for the cable modem is 255.255.254.0
The IPv4 subnet mask for the DSL modem is 255.255.255.0
 
You got lucky in some ways. You want the gateway on the dsl connection to be the static one and the gateway to be blank. Leave the cable modem interface get the gateway. The reason it partially works is it is using IPv6 only. You can if you want after it mostly work disable the IPv6 in your pc. It tends to cuase strange issues and there are almost no sites that use only ipv6. They have been saying ipv6 is the future for 20yrs but the ISP seem to give ipv4 better performance.

I assumed you had a router in front of the cable modem. It is not really a good idea to hook a pc directly up with out a router. The firewall on the PC is ok but with a router in between they can only attack the router not your PC. Be very sure that you keep the firewall rules updated if you are going to run without a router on the cable side.
 

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