[Beowulf] Re: question for licensed software users

David Mathog mathog at caltech.edu
Mon Jun 25 09:52:36 PDT 2007

> I have had eth0 and eth1 "change" identities as I patch the OS or add 
> ethernet cards. 

Recent versions of Linux, such as Mandriva 2007.1, have an /etc/iftab
and/or /etc/udev/rules.d/61-net_config.rules files.  Both of these
associate one specific MAC with eth0, eth1, etc.. 
The original intent was noble - they were trying to provide a
way to allow eth0 to always be the wired and eth1 the wireless
network connection, for instance.  However if these files
get the least bit out of sync with the actual hardware
all hell can break loose.  For instance, if one clones a single NIC
machine that uses these mechanisms the MAC won't match, eth0 won't be
used and a new eth1 will be magically created.  Unfortunately
the firewall doesn't know about eth1 and everything network
related then breaks.  Result, most likely the machine will hang
during boot.  Others have reported machines which create a new
eth# device at each boot, abandoning all the previous ones.  The general
fix for these sorts of bugs is to delete both of these files, and
at the next boot the udev file will be recreated and will match the
hardware.  I have not seen a need for /etc/iftab and just leave it deleted.

Now, back to Joe's problem, for the linux machines that are having
flexlm problems, if the nature of the problem is that eth0 and eth1
are swapping around at random, and those distros have these mechanisms,
be sure these two files exist and are configured properly so that
eth0 and eth1 are rigidly mapped to fixed MAC addresses.


David Mathog
mathog at caltech.edu
Manager, Sequence Analysis Facility, Biology Division, Caltech

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