Re: duplicate MAC addresses

[marty <marty@goodoldmarty.com>]

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John Stoffel wrote:
>>>>>> "marty" == marty  <marty@goodoldmarty.com> writes:
> 
> marty> Greg KH wrote:
>>>> On Tue, Aug 18, 2009 at 04:27:04PM -0400, marty wrote:
>>>>>> I got trouble...
>>>>>> (duplicate MAC addresses)
>>>> That's a bug in your hardware, have you asked your manufacturer to
>>>> resolve this for you?  That violates the ethernet spec...
> 
> marty> I have resolved that problem as of today. I found this was
> marty> caused by the software I had been using. If a hardware issue
> marty> remains, it is moot.
> 
> marty> The bonding driver/utilities normally sets the bond address to
> marty> the MAC of the first NIC. But it also set the MAC of the slave
> marty> (eth3) to the MAC of the first NIC. This persists through
> marty> reboots so that is how my MACs got duplicated.
> 
> marty> Resetting the MAC corrected those problems and everything works
> marty> fine now.
> 
> Doesn't this point to a udev rules problem?  What should happen if
> there are conflicting devices which both satisfy a condition, but
> where only one device is allowed to match?
> 
> Now I realize that with MAC addresses you're actually allowed to have
> multiple NICs on a host all with the SAME Mac addr, but only if
> they're on different segments.  Older Sun boxes all used to have a
> single MAC address across all ports.  This usually isn't a problem
> since the ethernet spec says that MAC addresses are local to the
> segment, and with switches and bridges, the segment is is limited.
> 
> Fails when you have bonding drivers and other HA tricks which I'm not
> up on though.  
> 
> John
> 
> 
> 

OOPS... Duplicate MACS won't work on a single box. On a network, yes.
Duplicate MACS mess everything up, because the lower networking layers do not
use IP addresses. They depend on the MAC to route the traffic.

I thought this was a udev problem. Greg KH suggested a hardware problem, but
I fixed it by removing the bonding driver from my config. Took a lot of debug.
I am using shorewall to configure iptables, which has another means to handle
multiple ISP's using packet marking. Works and as far as I can see no issues.

I was able to make the bonding driver work, but only if I manually corrected the
borked MAC beforehand. My changes didn't survive reboot. Something is broken in
that driver. I haven't looked as yet but I'm sure someone will discover it.

There was a issue with udev, however not a rule; the LFS bootscripts I use
were guilty. --retry-failed is in invalid option on udev-1.46. Caused a big
delay for some reason. I commented it out and it boots fast now.

BTW, this is a handy thing we can do on linux.
ip link set eth0 address 01:02:03:04:05:06
That will set a MAC address and survives reboot (on my system anyway).

Marty B.



-- 
An artist who is forced to work a specific schedule, is no longer
an artist; he is just hired help. Inspiration cannot be purchased.




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