Fibre Channel Physical Addressing
Two types of physical addresses are used in the Fibre Channel Protocol. The World Wide Names (WWNs), also known as World Wide Identifiers (WWIDs), are the physical addresses used in FCP communication. The WWNs are similar in concept to the Media Access Control (MAC) addresses in the Ethernet communication.
WWNs have two main types (see Figure 11-5):

Figure 11-5 WWNNs and WWPNs
- Port World Wide Name (pWWN/WWPN): This address uniquely identifies one FC port. On one FC device there will be as many WWPNs as the number of FC ports. For example, if an HBA has one FC port, then there will be one WWPN, which will identify that FC port. If there are two FC interfaces, there will be two WWPNs—one for each FC interface. Of course, the FC interface can be virtual, so there will be a WWPN to the virtual FC interface as well.
- Node World Wide Name (nWWN/WWNN): This is the physical address that uniquely identifies an FC device. It can be an HBA or an FC switch. This means that an HBA with one FC port will have one WWNN for itself and one WWPN for the FC port. If there are two FC ports on the HBA, there will be one WWNN for the HBA as an FC device and a WWPN for each of the FC ports.
It is important to know that the WWNNs and the WWPNs have exactly the same format. Because each physical address is used to uniquely identify an FC port or FC device, it has to be different and unique. There are rules for how these addresses are generated and assigned. As they are physical addresses, the FC components come with these addresses already burned in. However, they can be changed, just like the MAC addresses in the Ethernet devices. In this case, it’s important that the addresses are unique! An overlap between a WWPN and a WWNN or another WWPN will break the FC communication. This is very important when you work with the Cisco Unified Computing System, because the WWNNs and the WWPNs have to be created by you when FCoE is used. That’s why in the Cisco UCS, WWPN and WWNN address pools are used, which requires careful design and planning.
As already mentioned, both the WWNNs and the WWPNs have the same structure:
- The size is 64 or 128 bits (the most commonly used are 128-bit WWNNs).
- They are allocated to the manufacturer by the IEEE.
- They are hard-coded in the silicone of each FC device.
The structure of a WWN is either 8 or 16 bytes, as the specific format and length are defined by the Network Address Authority (NAA) bits. Then there is the organizationally unique identifier (OUI) of the manufacturer, in addition to other vendor-specific information.
The most common WWN format you will work with in the data center has the following characteristics:
- A size of 16 bytes (128 bits).
- The first 2 bytes, which include the NAA nibble and three additional nibbles, can be separated roughly as follows:
- 10:00: The NAA value of 1 followed by three 0s. Usually assigned to HBAs.
- 2x:xx: The NAA has a value of 2, but here the difference is that the other three nibbles, marked with x’s, can be used by the vendor.
- 5x:xx: Usually the WWNs assigned to vendors of storage equipment start with 5 as the NAA value.