Simple definition
A VMkernel port connects ESXi host services to a virtual switch and assigned network configuration.
Purpose and use
VMkernel port commonly refers to the logical interface used by a host networking service and attached to a virtual switch.
How does it work?
That interface depends on network connectivity, IP configuration and explicitly enabled services.
Example and verification
Correlate the vmk name, port group, VLAN and service during troubleshooting.
Points to watch
A VMkernel port is neither a TCP/UDP port number nor a physical Ethernet connector.
In short
Identify the logical interface, virtual attachment and physical uplinks separately.