If you are using vSphere Update Manager to upgrade or migrate a host from ESX/ESXi 4.x to ESXi 5.x, you must use manually assigned IP addresses for the hosts. Manually assigned IP addresses also referred to as static IP addresses.
DHCP IP addresses can cause problems during host upgrades or migrations performed with Update Manager. If a host loses its DHCP IP address during an upgrade or migration because the lease period configured on the DHCP server expires, Update Manager loses connectivity to the host. In this case, even if the host upgrade or migration is successful, Update Manager reports the upgrade or migration as failed, because it cannot connect to the host. To prevent this scenario, use manually assigned IP addresses for your hosts.