If you are using vSphere Update Manager to upgrade a host from ESXi 5.x to ESXi 6.0, you must use manually assigned IP addresses for the hosts. Manually assigned IP addresses are also called static IP addresses.
IP addresses that are requested by using Dynamic Host Configuration Protocol (DHCP) can cause problems during host upgrades that are performed with vSphere 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, vSphere Update Manager loses connectivity to the host. In this case, even if the host upgrade or migration is successful, vSphere Update Manager reports an upgrade or migration failure, because it cannot connect to the host. To prevent this scenario, use manually assigned IP addresses for the hosts.