Yellow Bricks

by Duncan Epping

vswitch

High physical switch CPU load?

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One of my customers experienced high CPU load on their physical switch. After some investigation they noticed broadcasts packets being sent every two seconds. The first reaction was Beacon Probing is probably enabled.

Unfortunately this wasn’t the case. But VMware GSS came to the rescue and pointed us towards a KB article. Apparently a bug has been identified in 4.0 which causes this behaviour:

src: http://kb.vmware.com/kb/1024435

Problem:

  • ESX sends Beacon Packets when vDS/vSwitch are connected to more than one uplink.
  • ESX server sends periodic broadcast of Beacon Packets even if the vSwitch/vNetwork Distributed Switch (vDS) is not configured to use Beacon Probing for Network Failover Detection.
  • These packets have the virtual MAC of the vmnic in the Source MAC Address field.

Workaround:

#esxcfg-advcfg -s 0 /Net/MaxBeaconsAtOnce

The customer implemented this workaround and the problem is gone… From what I have been told this issue does not exist in ESX(i) 4.1 so if you are experiencing it, an upgrade might be a better solution. In this case due to the size of the environment that was not an option.

Network loss after HA initiated failover

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I had a discussion with one of my readers last week and just read this post on the VMTN community which triggered this article.

When you create a highly available environment take into account that you will need to have enough vSwitch ports available when a failover needs to occur. By default a vSwitch will be created with 56 ports and in general this is sufficient for most environments. However when two of your hosts fail in a 10 host cluster you might end up with 60 or more VMs running on a single host. If this would happen several VMs would not have a vSwitch port assigned.

The most commonly used command when creating an automated build procedure probably is:

esxcfg-vswitch -a vSwitch1

This would result in a vSwitch named “vSwitch1” with the default amount of 56 ports. Now it is just as easy to set it up with 128 ports for instance:

esxcfg-vswitch -a vSwitch1:128

Always design for a worst case scenario. Also be aware of the overhead, some ports are reserved for internal usage. You might want to factor in some additional ports for this reason as for instance in the example above you will have 120 ports available for your VMs and not the 128 you specified.