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Re: [Xen-users] Switches and a moving MAC address

To: "Andreas (AH/TED)" <andreas.bach.aaen@xxxxxxxxxxxx>, xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] Switches and a moving MAC address
From: "Nick Couchman" <Nick.Couchman@xxxxxxxxx>
Date: Thu, 8 Sep 2005 08:34:11 -0600
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If I understand the way the XEN migration works, though, the MAC address of the guest O/S moves with the guest O/S to the new host machine (assuming, of course, that you're using virtual interfaces with Linux bridging).  Otherwise I don't think that the live migration would work very well, as routers, switches, and even the PC's that are connecting to the guest O/S would have to learn a new MAC address.  This would cause a loss of network connectivity longer than the fractions of a second that you lose when you migrate.  If you're using PCI devices in guest O/S, then you have an entirely different problem and you probably want to set your own MAC address on those devices so that it can migrate with the guest O/S.
 
(Some of the actual experts on this list might want to chime in with their two bits - I'm fairly new to XEN, so I'm just going off what I understand from documentation, other thread, etc.  Anyone else care to provide input?)
 
Nick Couchman
Systems Integrator
SEAKR Engineering, Inc.
6221 South Racine Circle
Centennial, CO 80111
Main: (303) 790-8499
Fax: (303) 790-8720
Web: http://www.seakr.com

>>> "Andreas Bach Aaen (AH/TED)" <andreas.bach.aaen@xxxxxxxxxxxx> 2005/09/08 05:03:27 >>>
Hi,

I have a succesfull XEN 2.06 installation with a DomU running with it's rootfs
over NFS. I can migrate this GuestOS between hosts on the same switches
network. I connect to my GuestOS over tcp (ssh).
The transfer of the GuestOS takes about 4 seconds, and with the live option it
should be for a very short period where the GuestOS actually is stopped.
After the transfer it takes 20-30 seconds before the GuestOS becomes
responsive again. Which kind of timeout it this?

When you move an IP address to another MAC address you typically send out an
unsolicited ARP to update the arp caches on the other hosts on the network to
ensure correct routing at once.
Are there any similar thing I could do to make sure that the switch will
broadcast the next packet for the MAC address that suddenly has moved to
another port?

Regards,
--
Andreas Bach Aaen System Developer, M. Sc.
Ericsson Danmark A/S tel: +45 89 38 51 00
Skanderborgvej 232 fax: +45 89 38 51 01
8260 Viby J Denmark andreas.bach.aaen@xxxxxxxxxxxx

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