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Possible Duplicate:
Two NICs, one server


I've clean installed a server with Ubuntu 10.04 LTS. The machine has two NICs and they're both on the same subnet ( bad, I know ). I've gotten around the kernel filtering packets by altering rp_filter as directed to here

On my previous install of this machine (Ubuntu 8.04 LTS), the network setup worked fine without this change in configuration. Now, the network is noticeably slower but functional.

Any idea how to improve this or test what's causing it?

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marked as duplicate by Ladadadada, Michael Hampton, Ward, Tom O'Connor, mdpc Jan 24 '13 at 3:17

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

The normal start point would be:

sudo tcpdump -i eth0 -w eth0.file
sudo tcpdump -i eth1 -w eth1.file

You can substitute the interfaces to match your configuration and try to match packets that go out and come back in.

I am rather curious as to the reason for having multiple interfaces on the same network:

Do you have enough traffic to saturate the link when traffic is combined?

If not I would suggest using bonding to provide for failover and simply assign the IP addresses you have on separate interfaces as virtual IPs on the bonded interface.

One thing I would look at although it doesn't much apply to the Intel hardware but on Sun machines where you could have a Single MAC across the board on all interfaces would cause spanning tree to be recalculated constantly as the interface used for traffic going out in the set up like yours would be picked in a round robin fashion. But as I said the single MAC doesn't much apply to Intel hardware but it might be a good place to start.

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