I’ve got this question several times from customers, friends, co-workers etc. Suppose now it’s time to make a small blogpost of it. (Also handy for VCP/VCDX exams)

A WWPN (World Wide Port Name) is physically assigned to a part in a Fibre Channel device, such as a FC HBA or SAN. It is the equivalent of the MAC address in the Ethernet protocol as it is supposed to be a unique identifier in the netwok.
The WWN’s are administred by the IEEE like the MAC Address is. The first few octets are assigned to a manafacturer, the rest is arbitrary.

The WWNN (World Wide Node Name) is a World Wide Name assigned to a node in a Fibre Channel fabric. It is valid for the same WWNN to be seen on many different ports on the netwerk.

The WWNN can be regenerated, the WWPN not :

(Screendump of VM properties below)

More info in this (usefull) document : Brocade_NPIV_ESX3.5_WP