[Beowulf] any creative ways to crash Linux?: does a shared NIC IMPI always remain responsive?

Rahul Nabar rpnabar at gmail.com
Mon Oct 26 11:50:26 EDT 2009

On Mon, Oct 26, 2009 at 8:11 AM, Bogdan Costescu <bcostescu at gmail.com> wrote:
> On Sat, Oct 24, 2009 at 11:13 PM, Rahul Nabar <rpnabar at gmail.com> wrote:
>> What surprised me was that even if I take down my eth interface with a
>> ifdown the IPMI still works. How does it do that ?
> The IPMI traffic is IP (UDP) based and by inspecting the IP header one
> can make a difference between packets with the same MAC and different
> IPs.

Actually, the MAC is different too. I have one NIC but it responds to
two MACs. I guess one is transparent to the OS and the other is
handled by the BMC.

> taken down, it's the Linux networking stack that doesn't see any
> packet coming in, however the BMC's network stack will still be
> active. That's the whole point of the BMC being a separate entity from
> the main system, so that its functionality remains undisturbed when
> something bad happens to the main system.

I see. So I assume the BMC's network stack is something that's
hardware or firmware implemented. It's funny that in spite of this the
IPMI gets hung sometimes (like Gerry says in his reply). I guess I can
just attribute that to bad firmware coding in the BMC.

>> Another mysterious observation was this: Whenever I took eth down via the OS there is a latent period when the IPMI stops
>> responding but then somehow it magically resurrects itself and starts working again.
> Without claiming that this is the best explanation: it's possible that
> the Linux driver talks to the hardware and takes down the link at the
> physical level. The BMC driver then detects this and brings the link
> back up so that it can continue to receive the IPMI packets.

You are probably right. THe explanation sounds reasonable to me. A
similar observation is for accessing the BIOS as well. The BMC stack
is not responsive right from the power-up. It does become responsive
for a bit but then the system drags it down (maybe when the BIOS hands
over to PXE). If I manage to "ipmitool sol activate" within this
correct window then I am able to see the BIOS. But that's pretty much
trial and error.

Beowulf mailing list, Beowulf at beowulf.org sponsored by Penguin Computing
To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf

More information about the Beowulf mailing list