How does Windows choose NIC for routing, no gateway?

[Patrick Coghlan]

I have the following:

- 2 NICs in each of my workgroup servers
- First NIC is connected to common hub (no routers in network)
- First NIC subnet is 192.168.1.0
- Second NIC is to be used for back-to-back CAT5 connection between
certain routers reserved for heartbeat-type packets between them
- Second NIC subnet is 10.0.0.0
- If I create static routes using Win2003 routing admin tool, the paired
servers can ping each other's 10.0.0.x address, so it does what I want

None of the NICs have a gateway configured, so I was curious how Windows
selects a route. Does it try the second NIC when it sees a 10.0.0.x
address, and the first NIC for everything else?

If I type ROUTE PRINT, I see a bunch of 192.168.1.x routing information,
but nothing for 10.0.0.0 (even though it's working).

I'd like to understand more about how this works at a basic level, since
I see this as a common requirement to send certain traffic out one NIC
(e.g., to the public internet) and other traffic out another NIC (e.g.
private network traffic).

 

[Mark L. Ferguson]

Use IPCONFIG, and perhaps NETSTAT /ANO to find your working IP.