<p class="MsoNormal" style="margin: 0in 0in 10pt;"><span style="font-family: Calibri; font-size: small;">I came across an interesting situation recently. After upgrading three VMware ESX 3.5 hosts to vSphere 4, I noticed that the hosts were not accessible on the network for 3 or 4 minutes after the reboot completed and console page appeared. This was troubling – I always sweat things out waiting for a server to come back on line following a major upgrade – but not that big of a deal since everything was working fine after a few minutes.<span style="mso-spacerun: yes;">  There were </span>no performance issues with the hosts or connectivity to the iSCSI SAN.</span></p>
<p class="MsoNormal" style="margin: 0in 0in 10pt;"><span style="font-family: Calibri; font-size: small;">Later I noticed the same thing was happening every time a VM was moved to another host with VMotion – it was not accessible on the network for 3 or 4 minutes following the move.<span style="mso-spacerun: yes;">  </span>Ouch!</span></p>
<p class="MsoNormal" style="margin: 0in 0in 10pt;"><span style="font-family: Calibri; font-size: small;">The ESX hosts were connected to two HP ProCurve 2510G 48-port switches.<span style="mso-spacerun: yes;">  After</span> validating the switch settings and searching the Internet for a solution unsuccessfully, I opened a case with HP ProCurve Support.</span></p>
<p class="MsoNormal" style="margin: 0in 0in 10pt;"><span style="font-family: Calibri; font-size: small;">The resolution was to upgrade the switches to a newer firmware release.<span style="mso-spacerun: yes;">  </span>Even though the switches were purchased a year apart, one within the last few weeks and one 12 months ago, they contained the same firmware release, Y.11.01, which was the initial release for the switch.<span style="mso-spacerun: yes;">  After</span> upgrading the firmware to the current release, Y.11.12, the problem went away. The release notes for the new version mention this fix that was implimented in release Y.11.08:</span></p>
<p style="padding-left: 30px;">■ If a client moves from one port or switch to another, the MAC address is not relearned on the new port until the MAC address timer expires on the original port.</p>

<span style="font-family: Calibri; font-size: small;">The interesting part for me is that the issue did not occur until after upgrading to vSphere 4.  ESX 3.5 had been running just fine on one of these switches for more than a year.</span>