netdev - bridging + load balancing bonding

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Date:	Thu, 22 Oct 2009 14:23:39 +0200
From:	Jasper Spaans <spaans@...-it.com>
To:	<netdev@...r.kernel.org>
Subject: bridging + load balancing bonding

Hi,

We're using the following setup for bonding and bridging, to be able to put
large amounts of data through multiple IDS analyzers:

                             +---[br0]----+     +--- eth1 ---(IDS machine 1)
(Span port from switch) -- eth0          bond0--+
                                                +--- eth2 ---(IDS machine 2)

eth0 receives network traffic, which should be passed to machines which are
connected to eth1 and eth2. These machines run an IDS package, and there are
two of those for performance reasons.

bond0 is configured to load balance the packets using "balance-xor", in this
case combined with xmit_hash_policy layer2.

However, we're seeing problems: packets from one flow do not end up at the
same IDS machine.  This is because this selection is not based on the source
_and_ destination mac addresses of the original packet, but on the mac
address of the bonding device and the destination mac address of the
package.

This is also clear in the code:
For example, in bond_main.c, in bond_xmit_hash_policy_l2:
	return (data->h_dest[5] ^ bond_dev->dev_addr[5]) % count;

Changing this to
	return (data->h_dest[5] ^ data->h_source[5]) % count;
fixes our problems, but is this harmful for packets originating locally (or
being routed?)

If not, can this be applied? Or does anyone have other ideas?

Thanks,
Jasper Spaans
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