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I have a problem on my Redhat computer.

I do have incoming traffic on a network interface, let's call it eth1. I also have outgoing traffic on another network interface, let's call it eth2.

When the route for outgoing traffic is not set, incoming traffic is correctly received on eth1 (a program is using information contained in this incoming flow), and, obviously, outgoing traffic from eth2 is not correctly routed since the route is not set.

When I set the route for eth2, my outgoing traffic is now correctly routed and there is no problem here. But incoming traffic on eth1 is not received anymore! It is very curious because I don't see how a route can block incoming traffic.

When using Wireshark on eth1, I see that packets are still received. When using Netcat, nothing is received.

If I delete the route, Netcat now receive the incoming traffic and everything works fine, but outgoing eth2 traffic is not routed anymore and I need this packets to be routed.

Is there a route mechanism I don't understand?

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  • Show us the routes you are adding and src & dst IPs of this incoming traffic.
    – MAQ
    Jul 28 '17 at 14:03
  • Thank you Christopher, disabling reverse path filtering solved my problem!
    – waterleek
    Jul 31 '17 at 14:42
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As Christopher said:

Does this information help? Maybe not the same scenario, but probably relevant. Separate Network Traffic on Two Network Interfaces

This helped as disabling reverse path filtering solved this issue.

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