How does Windows XP Pro determine which network connection to use when multiple network connections exist on a PC?

Posted on 2006-11-16
Medium Priority
Last Modified: 2010-04-09
This is a theoretical scenario I am using solely for the purpose of understanding how Windows works.

Let’s say I have a laptop running Windows XP Pro and it’s connected to my home network via the onboard wired NIC, and then I establish a VPN connection to my company’s network creating a second network connection, and then I connect to my neighbor’s unsecured wireless network creating a third network connection.

How does Windows XP Pro determine which network connection to use when multiple network connections exist on a computer? Thanks.
Question by:WineGeek
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Accepted Solution

LucF earned 2000 total points
ID: 17960876
Hi WineGeek,

Please start with reading the following document:
Default Gateway Behavior for Windows TCP/IP

It explains pretty clearly how Windows will handle multiple gateways.

If you're using the windows XP PPTP client for the second connection (the VPN one) it's rather simple, you have one connection directly to the internet and one VPN. The PPTP client in Windows can be set to use the gateway on the remote network (default setting) or not to use that one. (http://www.firewall.cx/pictures/chris/pptp-remote-gateway.gif)

In any case, you can see how windows will route the traffic if you take a look at the routing table by typing the "route print" command in a command prompt.


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Expert Comment

ID: 17970528
Windows doesn't have the capability of intelligently determine the network connectivity, so you don't get any loadbalancing stuff here which you'll get with networking equipments.

Simple, 2 NIC configurations are allowed (which are to indicate 2 connections), but only one of them can have a default gateway, otherwise you can expect the unexpected.

In industry the 2 NIC scenario's are used, in such cases only one of the NIC should have a default gateway and only then the expected traffic flow would happen. Usually like the SBS servers/ISA servers do this.



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