freevrrpd (was: My planned work on networking stack)

[Brooks Davis]

On Wed, Mar 03, 2004 at 07:14:31PM +0200, Cole wrote:
> 
> The problem with freevrrp on vlan is that the ether MAC address gets
> changed on the vlan device which is then different to the parent
> device that the vlan was attached to. Since the vlan then has a
> different ether MAC to the parent device, i dont think the parent
> device is passing the packets back to the vlan device.
>
> What i tried to implement was a patch to the vlan device to update the
> parent device's ether MAC address. I dont do this kind of programming
> so i really dont have much skill with device drivers, i asked a few
> devs that worked on the vlan device, and i either got no reply, and
> the ones that did reply, only did so once and no further.

You can't just change the parent, you will also have to change the
MAC of any other vlans of the parent.  This requires scanning the
interface list for vlans and checking if they are children of the parent
interface.  This is non-trivial, but doable.  If a patch that did this
were written and met style(9), I'd probably be willing it commit it.  It
won't help people who want to abuse vlans to let a server do fail over
for multiple machines on different subnets though.

The real solution is to modify the Ethernet code to allow processing of
select, non-multicast MACs up the the point where they are sent to the
vlan which can decide which MACs it's actually going to pay attention
to.  This means you have to do some filtering in software (probably
all filtering on many (most?, all?) nics).  I think this could be done
by reordering parts of ether_demux and modifying the way packets which
don't match our "primary" address are handled.  This looks do-able, but
care are would have to be taken to ensure things were done correctly and
that performance for the other 99.999+% of the world wasn't measurably
harmed.

-- Brooks

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