vCenter 6.0 u3 - 10.120.10. x
host 5.5 u3 - 10.120.10.x
host 6.0 u3 - 10.120.12.x
is it possible to use vMotion to move a machine from an ESXi server in one subnet to an ESXi server in another?
If there is a firewall, which port should I open?
Check if the following VMware KB article helps:Incoming and Outgoing Firewall Ports for ESXi Hosts
Networking Best Practices for vSphere vMotion
Open an 8000 port between the host and the host
Should vcenter and host also open port 8000?
Only between hosts.
The hosts obviously need to be able to chat with vCenter to set up the session.