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Sorry, I put the wrong KB article on my first reply, but have changed to point to the correct VMware KB article that shows how to check bi-directional traffic, see: ESXi/ESX host disconnects from vCenter Server 60 seconds after connecting (1029919) | VMware KB

To verify if bi-directional traffic is allowed:

1. Download Wireshark from http://www.wireshark.org/ and install it on the vCenter Server system.
2. On ESXi, enable Tech Support Mode. For more information on enabling Tech Support Mode, see:
   
   
   • For ESXi 4.1 and 5.x: Using Tech Support Mode in ESXi 4.1 and ESXi 5.x (1017910)
   • For ESXi 4.0: Tech Support Mode for Emergency Support (1003677)
3. Download the Python script attached to this article (udp_client.py) to the ESXi/ESX system in question.
4. Edit the udp_client.py script on the ESXi/ESX host using a text editor. Modify the line, "host = '192.168.1.1'" and replace 192.168.1.1 with the IP address of the vCenter Server system.
5. Start Wireshark on the vCenter Server system.
   
   
   1. In the Filter field, enter ip.src==IP_of_host and udp.port==902. Replace IP_of_host with the IP address of the ESXi/ESX host in question.
   2. Click Apply.
   3. From the Capture menu, select Interfaces and click Start next to the NIC used for vCenter Server IP traffic.
      
      
6. From the ESXi/ESX host, run this command:
   
   python udp_client.py
   
   The total number of packets sent, the port, and the destination address are displayed.
   
   
7. On the vCenter Server system, watch the Wireshark screen for any packets showing up that match the filter applied.
8. If no packets are received, this indicates that something is blocking UDP traffic over port 902 from the ESXi/ESX host to the vCenter Server system. Inspect the physical networking environment and any software-based firewall on the vCenter Server system.

Ensure that these ports are open in the firewall between vCenter Server and the ESXi/ESX hosts:

• 902 - UDP & TCP
• 443 - TCP