I recently completed a VMware VI 3.5 to vSphere upgrade in a small environment (5 hosts, 80 VM's).  Being a small environment, the upgrade was planned for one big overnight blitz.  Unfortunately, the size of the environment did not afford a test environment to uncover potential issues before the upgrade.  The upgrade to vSphere itself went swimmingly (the vCenter server had been upgraded a couple weeks earlier).  However, some things in the environment started to go wonky once the upgrade was complete.  Specifically, name resolution (DNS), DHCP, WINS, Group Policy, and really anything … [Read more...]