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Author Topic: Virtual servers flip-flopping between switches  (Read 1873 times)


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Virtual servers flip-flopping between switches
« on: May 16, 2011, 05:37:03 PM »
Hi all,

This is a minor query, but I'm seeing some of my virtual servers flip-flopping from the switch the physical ESX hosts are connected to, to another one elsewhere on the network.

I have two physical ESX hosts, each of which is connected via two 1Gbps NICs configured as a trunked 2Gbps Etherchannel link to a Cisco 2960G (call that switch1).  That switch is connected to a stacked pair of 3750s at the core (switch2a and 2b), which in turn link to another 2960G (switch3) via another Etherchannel link with one interface on each of the 3750s.

Most of the time, Nedi correctly sees the virtual machines as being on either interface Po1 or Po2 on switch1.  Occasionally (perhaps 2-3 times a day on average, but some VMs seem to go days without doing this, then 20 times in one morning) it detects as having switched to interface Po1 on switch3.  Never switch2 (or any of the other switches on the network).  On the next scan, it reverts back to the correct pickup on switch1.  It doesn't seem to follow a pattern where all VMs will get picked up in the wrong place and then all will return.  It does appear to just be random as to which ones if any will be wrong.

Prior to configuring the ESX hosts to have a trunked connection and each host just had two regular interfaces, things seemed fine, and nedi only picked up a change in the interface when VCentre moved the virtual machine from one host to another.

Still running 1.05 at the moment, (eagerly) waiting for a full release of 1.06.

Is this just something I have to live with?  Is there anything I can do to minimise it doing this?  Is it something to do with the order it scans?  Anything odd with either the Cisco or VMWare configuration that can lead to this?  It's not something I want to go to hugely disruptive measures to fix, but if it is something obvious then it does at least cut down on displaying a thousand or so interface changes when I view a node...