how is the MAC for tap(4) computed?
Dan Nelson
dnelson at allantgroup.com
Mon Nov 4 17:10:03 UTC 2013
In the last episode (Nov 04), Aryeh Friedman said:
> There seems to be a very high rate of MAC address collisions when tap is
> running on different machines.... is there anyway to make the selection
> of MAC more random
It looks like it's generated based on the number of ticks since boot, plus
the unit number of the tap device:
http://fxr.watson.org/fxr/source/net/if_tap.c#L434
So if you have devices created on boot on a bunch of machines, chances are
high that you'll get conflicts. Maybe instead of using the 'ticks' value,
kern.hostid could be used instead? That has much better randomness than
'ticks'.
--
Dan Nelson
dnelson at allantgroup.com
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