Redirect traffic through a computer to another connected to the same switch

Question

I am trying to setup a single sender, single bottleneck and single receiver network.

The router in the image is a computer that has ip_forwarding enabled. PC1 has the default gateway set to the IP address of PC2.

PC1 and PC2 are on the same subnetwork (10.32.20.*) and PC3 is on a different subnet(10.32.21.*).

Yet, only occasionally does data flow through PC2, the router. The data seems to be flowing directly between PC1 and PC3 via the switch.

My question is how to ensure that traffic flows through the router and doesn't flow directly at the switch.

Add a second network card to PC2 and place it in between PC1 and the switch? — Reaces, Jan 27 '15 at 12:50
Yes, but we didn't want to buy a new network card. Any way to do this without that? — Darshan Rai, Jan 27 '15 at 12:59
I believe so. The problem is that we don't have access to the switch, so whatever configuration we'll need to do has to be done at the sender. — Darshan Rai, Jan 27 '15 at 16:46

score 0 · Answer 1 · answered Aug 15 '16 at 12:03

I would guess that the behaviour you are seeing is caused by ICMP redirects.

When PC1 first sends a packet it goes to PC2. PC2 then sends an ICMP redirect informing PC1 that PC2 is actually on the same network despite being in a different IP subnet.

If my guess it correct you should be able to fix things by either disabling sending of ICMP redirects on PC2 or disabling reception of ICMP redirects on PC1.

Redirect traffic through a computer to another connected to the same switch

1 Answers1