My linux box has a duty. It has to forward IP packets for a "private" network which it doesn't belong to.
The network is "private" has the meaning that the hosts that belong to the network have IP addresses that are unique only between them. Say that the network is formed by 4 nodes: "a", "b", "c", "d", with their IP addresses: 10.0.1.1, ..., 10.0.1.4. The nodes "a", "b" and "c" are connected, but the only way from "c" to "d" is through my box, let's call it "x". The problem is that "x" has to live inside another "private" network, and in this other network the address of "x" is 10.0.1.4. When I send a PING-request from "c" to "d" the packet goes to a specific NIC of "x". Thanks to some carefully designed iptables+ip-rule tricks in "x", the PING-request is effectively relayed from "x" to the node "d", although "x" has the same IP as the destination of the packet. Now the node "d" sends a PING-reply to "c". This packet goes to a specific NIC of "x". There, the same tricks would send the packet to "c". But this is not happening. I suspect that the problem is that the box "x" refuses to relay a packet that has an IP source equal to one of its local IP addresses, although this IP is assigned to another NIC. I have this suspect because of the tcpdump traces that I have collected. But I don't seem to succeed in finding other evidences (I looked into dmesg and /var/log/syslog). Is there a tunable in linux to change this behaviour? I want to say to "x": When a packet comes in through NIC0, relay it without bothering if it has your IP as source address. TIA --Luca -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
