Dual nic on a server

[Luis Fernandez De Jauregui]

Hi,
 
If I have a Silicon Mechanics server with two NICs connected to different networks. When I send a packet to a remote host, it goes through my routing tables and sends the message out the correct interface with it's corresponding IP address as the source IP. Every now and then I see some packets go out on that same interface but with the IP address assigned to the other interface as the source IP.
 
My question is, how does the OS choose what IP address to use as the source IP? I thought that it was going to go through the routing tables, choose the interface and then put the IP associated with that interface as the source, but it looks like it is not always doing that. ANy ideas?
 
Thanks,
 
Luis Emilio Fernandez de Jáuregui
Sr. MSS GSM/UMTS Lab Infrastructure
Nortel
luisf at nortel.com <mailto:luisf at nortel.com> 
Telephone (972) 684 1472 / ESN 444 1472
Fax (972) 684 3715
 
 
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