Simultaneous Use of two Ethernet Gateways

scarince

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Jan 2009
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This is arguably a Windows question, but it must be applicable to a lot of people.

When we go to the shop floor to connect to a machine network, we use our wireless adapter to stay connected to resources like network drives and the Rockwell activation server, and we use another adapter (usb or built-in) to plug into the machine. An ethernet gateway address isn't usually needed on the machine network.

The newer lines in our plant have more complicated networks of PLC's linked through NAT's. Sometimes I need to go online with a few PLC's at once and the NAT's are configured with a translation for the laptop. As long as my laptop has the NAT identified as a gateway, it'll work great. I can go from the Private side of one machine NAT and connect to the other PLC's as well, using their Public addresses.

BUT, when I set a gateway address for the machine network on the laptop, most of my wireless resources stop working because DNS requests are going unanswered because the laptop is picking the machine gateway as the address to use. If I remove the gateway entry, everything works fine on the plant side, but now I can't reach the networks on the Public side of the NAT.

So the question is, is there a correct configuration in Windows (7) that supports two different gateways on two network adapters at the same time? It seems like there must be but I am not having any luck.

Thanks.

B
 
Sure, the wonderful world of routing is fun.

First thing to know, The issue you're having is when you stick a gateway into a network interface, windows will consider that the default gateway unless told otherwise.

So conceptually, you cannot have more than 1 default gateway, doesn't make sense right?

Your DHCP wireless connection will likely come w/ a gateway and then you configure a gateway on the wired connection and now windows is confused.

So instead of setting a gateway for the wired side, you can setup static routes that will tell windows to go to a specific adapter for specific network traffic and vice versa.

https://technet.microsoft.com/en-us/library/cc957843.aspx
Different os, but a decent set of examples.
https://www.techrepublic.com/article/understand-the-basics-of-linux-routing/
https://docs-old.fedoraproject.org/...ec-Static-Routes_and_the_Default_Gateway.html
 
I had a similar problem with a SCADA micro PC where I had it set up with a wired connection to the PLC, and a wireless connection to the internet for remote access. Problem was, as soon as I plugged the wired connection in, the OS (Windows 10 in this case) seemed to go "oh great! I have a hardwired connection now, so I can forget about the wi-fi!"

I can't remember exactly what the solution was, but I know I got into things like preventing the computer from turning off the wi-fi adaptor to save power, and setting the network priority via command line, and all sorts of tricks like that.

Seems like Dravik probably has some more useful information for you, but maybe my 2c worth will fill in a blank somewhere at some point ;)
 
I'm going to assume the network being connected through via the wireless adapter is not the same one that the NATs expose their private-network PLCs to. Otherwise you could just come in through those public addresses using the wireless adapter.
 
I'm going to assume the network being connected through via the wireless adapter is not the same one that the NATs expose their private-network PLCs to. Otherwise you could just come in through those public addresses using the wireless adapter.


Yes, you are correct. The assembly line is a string of separate machines, each with a NAT so that I can use P/C'd tags to coordinate the line. But the line is not attached to our plant networks, yet.

The wireless connection is the totally separate enterprise network that supports the factory with all the usual printers, file servers, SAP, etc etc.
 

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