ESX Server firewall is not configured to High Security.

ESX Server includes a built in firewall between the service console and the network. To ensure the integrity of the service console, VMware has reduced the number of firewall ports that are open by default. At installation time, the service console firewall is configured to block all incoming and outgoing traffic except for ports 902, 80, 443, and 22, which are used for basic communication with ESX Server. This setting enforces a high level of security for the ESX Server host. Medium Security blocks all incoming traffic except on the default ports (902, 443, 80, and 22), and any ports users specifically open. Outgoing traffic is not blocked. Low Security does not block either incoming or outgoing traffic. This setting is equivalent to removing the firewall. Because the ports open by default on the ESX Server are strictly limited, additional ports may need to be open after installation for third party applications such as management, storage, NTP, etc. For instance, a backup agent may use specific ports such as 13720, 13724, 13782, and 13783.