If your environment does not include vCenter Server, clients can connect directly to the ESXi network.
You can connect to a standalone ESXi host in several ways.
VMware Host Client
One of the vSphere command-line interfaces
vSphere Web Services SDK or vSphere Automation SDKs
The firewall requirements for standalone hosts are similar to requirements when a vCenter Server is present.
Use a firewall to protect your ESXi layer or, depending on your configuration, your clients, and the ESXi layer. This firewall provides basic protection for your network.
Licensing in this type of configuration is part of the ESXi package that you install on each of the hosts. Because licensing is resident to ESXi, a separate License Server with a firewall is not required.
You can configure firewall ports using ESXCLI or using the VMware Host Client. See vSphere Single Host Management - VMware Host Client.