Setting Up Dual Nic's on Windows XP

Posted on 2006-11-30
Last Modified: 2012-05-05
I would like to setup my dual nics as follows:

Nic 1: connect to internet via router (DHCP or static)
Nic 2: connect to local switch which is connected to another router and then to the internet

I do have two internet connections and I want the XP pc to access the internet via Nic1 and I would like Nic 2 to be used really only for applications like remote desktop and file sharing with other PC's that are also connected to the local switch.

Can this be done?

Question by:tdavis1198
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Accepted Solution

Trilotech earned 75 total points
ID: 18048439
Just set up your gateway on NIC 1 and leave the gateway for NIC 2 empty. All local traffice to NIC 2 subnet will go there automatically. Any other traffice will go out your gateway address of NIC 1.

Expert Comment

ID: 18048809
Trilotech is on the right track, but I'm not convinced that his response will solve your problem. You'll want to have both gateways entered on those NICs, but apply persistant routes for the specific connections you desire.

See this link:

Remember that you'll need to use the -P switch to make it persistant, or else you'll loose the routes you've added at the next system reboot.

Follow the standard procedures for routing.. making sure to have all traffic go out the gateway for NIC 1 by default. I think the way to do this is to add a route for (which typically means all traffic) placed at the bottom (or top depending on that table) of the routing table. The packet that is addressed to a machine on the local subnet will be checked against the routing table and then go out NIC 2.

Ira @ KVR

Expert Comment

ID: 18048896
You only want to go to the internet via NIC 1 correct? NIC 2 is only for the local LAN. So only the gateway on that NIC needs to be set.

You should only ever have one default gateway... This means it is the last route when no other is available.
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Expert Comment

ID: 18048914
You may be correct, however, I have a machine at my house working just like the setup that I described. I am aware of the warning that Windows gives you upon hitting apply with a second gateway, but if you control the routes with a routing table it works as expected.

Expert Comment

ID: 18048938
Yes but you are controlling the routes with your routing table and NOT the second gateway...

Expert Comment

ID: 18048952
Are you convinced that all of the traffic addressed to the local subnet will use the second NIC without a routing table?

Expert Comment

ID: 18050007
Of course it will. That is why it is called local traffic. Only traffic outside your subnet is routed, thus requiring a route.

Any traffic that is on the same subnet as your NIC will go out that NIC and does not get routed. If you are on a LAN only with local computers and no internet, you would not even have a default gateway. All communication would be local.

If an IP packet is addressed to an address NOT in your subnet your computer looks to its routing table. It starts at the top, where the most specific settings are, looking for a route. AS SOON AS IT FINDS ONE it uses it and does not even continue to parse the routing table. This is why it is pointless to have a second default gateway. Whichever one is first on the list will ALWAYS be used if no other routes have been found.

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