2 ethernetcards in one pc

[230173]

I've got a pc with two ethernet cards: a 3com etherlink 10mb ISA and a 3com etherlink 100mb PCI. The PCI cards is connected to the network and has a fixed IP address. The other card is connected to a PLC with a crosscable. This one has a fixed IP address and a subnetmask but no gateway. So here's the problem. I try to ping to that PLC but no luck. So i think he's trying with the wrong card. How do you know which card he chooses for a ping?

 

[manarth]

a ping (or indeed any message sent through TCP/IP) will go down the shortest route it knows of to get to it's destination - the route is determined by the routing table held on the machine...
Your NICs *should* (doesn't always happen!) have their own unique IP addresses.

When you tell the machine to ping the PLC's IP address, your machine looks at it's routing table and decides which IP address to send the message down - the IP belonging to the 10MB card or the IP belonging to the 100MB card.

You determine which card your ping will go down by specifying which of the 2 IP's represents the shortest route to the destination IP (belonging to the PLC)

The fix to this is to update your routing tables - how to do it will depend on your O/S.
I found this website useful in explaining how to do it across Microsoft and Unix systems -

http://www.pku.edu.cn/academic/research/computer-center/tc/html/TC0310.html

Hope this helps, Marc.