My Linux (kernel 3.17) computer has more than one NIC: eth0, eth1, (and/or eth2...)
I have several PC connected to each of them:
PC0 <---> eth0 (192.168.1.100) PC1 <---> eth1 (192.168.1.101) PC2 <---> eth2 (192.168.1.102)
An application on the Linux computer started threads to listen to 192.168.1.100 (and the other two). Upon receiving a packet from PC0, the thread replies. How do I guarantee the reply never go through eth1 or eth2 although they have same subnet mask? Similarly, upon receiving packet from pc1, the reply should never go through eth0 or eth2.
Ideally, to achieve what I said, I should use three completely different subnet, such as 10.0.0.1, and 172...., but my colleague suggests it could work, so I am here to find peer opinions. The kernel is in my control, I build it, so any solution to make it work can be proposed.
Why three NIC on same subnet? Eth0 is the main IP address that is statically assigned during Linux boot. It shouldn't change but could change if needed. The question is: what if the field people accidentally assigned eth1 and eth2 to have same subnet with eth0? Will my application reply only to eth0 if the socket listens on eth0 at a certain port?
Possible Routing Table
the rule is to go through the NIC if it is where the request is from. I copied from somewhere
ip route add 172.16.10.0/24 dev eth0 src 172.16.10.10 table 10 ip route add default via 172.16.10.251 table 10 ip route add 172.16.10.0/24 dev eth1 src 172.16.10.20 table 20 ip route add default via 172.16.10.251 table 20 ip route add 172.16.10.0/24 dev eth0 src 172.16.10.10 ip route add 172.16.10.0/24 dev eth1 src 172.16.10.20 ip route add default via 172.16.10.251 ip rule add from 172.16.10.10 table 10 ip rule add from 172.16.10.20 table 20 ip route flush cache