Martinez, Michael wrote: > Let's say you have a Linux system with two NIC cards each on the same > subnet. Let's say the system wants to talk to another computer on the > subnet. How does the kernel decide which NIC to use? I believe the last initialized card is given the subnet route. I don't believe they automatically equalize. > Is there a way to force the use of a particular NIC for an > application running under a particular username? Yes, at least for outgoing connections. Setup a new routing table dedicated for this new channel. The only route will be default -> some_network. I assume you can do this yourself. The second part is forcing data to/from the user to go out on the correct interface. # Routing # Any traffic with 111 fwmark should exit network if if_second_one(eth0,eth1,...) ip rule add fwmark 111 table 111 ip route add default dev $if_second_one table 111 # Tell the system to mark any packet leaving the system coming from root as 111 iptables -A OUTPUT -m owner --uid-owner root -j MARK --mark 111 # When sending the marked packets over the network, send it as the IP address of the second NIC. iptables -A POSTROUTING --mark --mark 111 -j SNAT $Outgoing_IP
