AW: AW: [Users] Veth mac generation

Dietmar Maurer dietmar at
Fri Jun 13 02:52:34 EDT 2008

> Do I understand correctly that you actually experience the 
> following problem:
> 1. veth MAC address is lower then your ethX MAC.
> 2. so brX is assigned min(vethX-MAC, ethX-MAC) which is vethX-MAC.
> 3. and what is the your problem with that? that host system 
> MAC changes dynamically and networking breaks or what?

The host gets unreachable for about 20 seconds (because ARP mappings
are wrong now)

> I just can't see how fully random 6 bytes MAC can help. 
> Because sometimes it will be "low" enough as well and you 
> will hit the problem anyway.

Well one idea was to assign macs starting with 'fe' - but ist not
a good idea anyways.

> If I got your problem right then I can advise you a possible 
> solution - in RHEL5 kernel we have a functionality called 
> "via_phys_dev" (triggered by BRCTL_SET_VIA_ORIG_DEV ioctl). 
> This forces kernel to work with original interface ethX 
> (first added to bridge) and pass the traffic to it. This 
> allows to add ethX to bridge w/o need to propogate it's 
> netfilter rules and other settings to brX.

Interesting - thanks for that hint.

- Dietmar

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