netdev - Re: [PATCH] bonding: allow bond in mode balance-alb to work properly in bridge

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Date:	Fri, 13 Mar 2009 22:39:32 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	jgarzik@...ox.com, davem@...emloft.net,
	bridge@...ts.linux-foundation.org, fubar@...ibm.com,
	bonding-devel@...ts.sourceforge.net, netdev@...r.kernel.org
Subject: Re: [PATCH] bonding: allow bond in mode balance-alb to work
 properly in bridge

On Fri, 13 Mar 2009 19:33:04 +0100
Jiri Pirko <jpirko@...hat.com> wrote:

> Hi all.
> 
> This is only a draft of patch to consult. I'm aware that it should be divided
> into multiple patches. I want to know opinion from you folks.
> 
> The problem is described in following bugzilla:
> https://bugzilla.redhat.com/show_bug.cgi?id=487763
> 
> Basically here's what's going on. In every mode, bonding interface uses the same
> mac address for all enslaved devices. Except for mode balance-alb. When you put
> this kind of bond device into a bridge it will only add one of mac adresses into
> a hash list of mac addresses, say X. This mac address is marked as local. But
> this bonding interface also has mac address Y. Now then packet arrives with
> destination address Y, this address is not marked as local and the packed looks
> like it needs to be forwarded. This packet is then lost which is wrong.
> 
> Notice that interfaces can be added and removed from bond while it is in bridge.
> Therefore I introduce another function pointer in struct net_device_ops -
> ndo_check_mac_address. This function when it's implemented should check passed
> mac address against the one set in device. I'm using this in bonding driver when
> the bond is in mode balance-alb to walk thru all slaves and checking if any of
> them equals passed address.
> 
> Then in bridge function br_handle_frame_finish() I'm using ndo_check_mac_address
> to recognize the destination mac address as local.
> 
> Please look at this and tell me what you think about it.
> 
> Thanks
> 
> Jirka
>

A better and more general way to do this have the dev_set_mac_address
function check the return of the notifier and unwind. Then any protocol
can easily prevent address from changing.
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