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This is using CentOS 5.5. I have two dual port NICs on a server:

NIC1: eth0, eth1

NIC2: eth2, eth3

I have an ssh and vnc session open to the ip address on eth2. When I disable eth0 (ifdown eth0), my sessions to eth2 disconnect and I no longer receive a response when pinging that ip address. What could be happening?

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eth0 and eth2 are on the same network, so I suspect data is coming in on eth2, but going out of eth0 due to the routing table. – PiNoYBoY82 Jan 27 '11 at 16:21
If they are on the same network, why not create a bond interface? – SpacemanSpiff Feb 4 '11 at 21:49

You can run tcpdump -i eth0 and see if the packets are going out via eth0 instead of eth2.

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This would be my guess as well. you can disable it (so that connection replies go out the interface they originally came in on) with echo 0 > /proc/sys/net/ipv4/conf/eth2/rp_filter and/or add net.ipv4.conf.eth2.rp_filter = 0 to /etc/sysctl.conf – Patrick Feb 4 '11 at 23:18

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