PC with 2 NICs in 2 networks

I have to setup a peer to peer network at an office that is actually 2 separate companies that are sorta related. Without going into the unnecessary details, what I am asked to do is this:

All of the computers are Windows XP Pro. Each has a NIC. There are two rooms. Each room is occupied by one company. Each room has its own DSL modem and router/switch. Because these 2 companies used to be one company and the two are in the process of separating, the new offshooting one still needs to access data from the first company.

Ok, so far, there is this one computer that is technically owned by the new company. This PC has 2 NICs. One NIC is physically connected to the router of the old company at 192.168.1.1 as the gateway while the other NIC is connected to the other router belonging to the new company at 192.168.0.1. Therefore, this computer has access to shared resources of both companies. I renamed the workgroup names differently so that on this particular PC, the two workgroups both appear as two icons in Network Places. Everything is fine now, but I have a problem. Well, more like a petpeeve.

When this computer goes to the Internet (and it can), how does it know which router to use and therefore which DSL connection to use? How does Windows XP pro resolve this? Actually because the second newer company is smaller, their network load is not as great as the older and larger company. Therefore, I want this PC to use the newer company's network connection to go to the Internet because of the lesser network congestion. Is there a way I can force XP on this machine to use ONLY the new company line for Internet access?

 

Assuming that you meant the PC has a NIC connected to each switch then remove the gateway address of the router you don't want it to use for internet access.

 

Actually, that was exactly what I did. I configured this PC, with respect to the NIC that is connected to the old company's network's switch, with a manual TCP/IP setting where I only put in a static IP in the 192.168.1.x and a subnet of 255.255.255.0. I left the gateway and dns fields blank.

Like I said, everything is fine because this computer can access both networks and the Internet. What was left to do was how to make sure that XP in this computer does not even TRY to use this NIC with the IP of 192.168.1.x to access the Internet.

So you think that when XP sees that there is no gateway IP and DNS entry for a NIC, XP will not even try to use this NIC for Internet access? In other words, XP does this (or does NOT do this to be more precise) implicitly as opposed to having a check box somewhere where we can explicitly tell XP not to use this NIC for the Internet?

 

If you have both NICs set with a default gateway, the PC will only use one of them. You can tell which one by doing a "route print" at the command prompt. Default routes are those to destination 0.0.0.0. There will be either one or two. If two, it will be the lower one that your system uses. Which one is used I expect depends on the binding order, but may also take into account hop matrix.

As you have found and Newt stated, setting only one default gateway will force the system to use the correct route. Otherwise you could experiment with a "route add" to change the order.

 

It may try - I don't think so but I really don't know how smart the network pieces are. It will fail if it tries but fail fast enough you won't notice.

Most of my network knowledge is practical rather than theoretical and the 'try vs. not try' needs theory knowledge.

ReggieB has tons more theory than I ever will.

 

I work as a tech, hoping to migrate to system administration of Windows networks. I like networking above all else, and from all my experiences with it, I can say for sure that networking is like a piece of art. A network is more than the sum of all its parts. A network is almost a life form in away with different organs working together to create a harmonious whole. Asides from the logical protocols and layers, there is a mysterious aura to it. Anyone who witnesses a remote desktop session can tell you that.