with a command prompt you can see the routing table:
route print
Code:
1) Active Routes:
2) Network Destination Netmask Gateway Interface Metric[b]
3) 0.0.0.0 0.0.0.0 192.168.0.1 192.168.0.4 20[/b]
4) 127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1
5) 192.168.0.0 255.255.255.0 192.168.0.4 192.168.0.4 20
6) 192.168.0.4 255.255.255.255 127.0.0.1 127.0.0.1 20
7) 192.168.0.255 255.255.255.255 192.168.0.4 192.168.0.4 20
8) 224.0.0.0 240.0.0.0 192.168.0.4 192.168.0.4 20
9) 255.255.255.255 255.255.255.255 192.168.0.4 192.168.0.4 1
10) Default Gateway: 192.168.0.1
===========================================================
Well all know that 127.0.0.1 will never leave our system so lines 4+6 lead to only internal services
with the ip address from ipconfig == 192.168.0.4, lines 5,+7+8+9 are the system itself on the LAN
that leaves ONLY 192.168.0.1 (the gateway address) as a means to leave the box.
add all the NICs you please and you still get only ONE default and all nonspecific outbound traffic will exit your system via the single gateway shown on line (3)
btw: adding a second nic, say on 172.16.1.* will create another route like
Code:
172.16.1.0 255.255.255.0 172.16.1.0 172.16.1.0 20
which will only send traffic to a specific destination on that subnet 172.16.1.0/24