On Mon, Oct 26, 2009 at 8:11 AM, Bogdan Costescu <bcoste...@gmail.com> wrote: > On Sat, Oct 24, 2009 at 11:13 PM, Rahul Nabar <rpna...@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. -- Rahul _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org sponsored by Penguin Computing To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
