This document discusses licensing options when managing both ESX 3.x/ESXi 3.5 hosts and vCenter Server 4.x. There are four options: use a single license server for both, use separate servers, use a server for vCenter and host-based licensing for ESX hosts, or upgrade all hosts to ESX 4.x which allows centralized management with vCenter. It also provides instructions for configuring the license server connection in vCenter and for ESX hosts. Troubleshooting steps are included to check the license server service, that it is listening, and its status.