World Wide Name (WWN)

What is World Wide Name (WWN)?

A World Wide Name (WWN) is a unique identifier that is hard-coded into each Fibre Channel (FC) device by the device's manufacturer. WWNs provide a method for identifying FC devices across the network.

Each WWN conforms to one of several formats defined by the Institute of Electrical and Electronic Engineers (IEEE). As a general rule, each format includes a 4-bit Network Address Authority (NAA) format code and a 24-bit manufacturer identifier that's issued by the IEEE, along with vendor-specific information.

The use of four codes (C, D, E and F) for the Mapped EUI-64 format has to do with how the manufacturer ID is represented within the WWN. However, all four codes refer to the same format. With the EUI-64 format, the manufacturer ID abuts the format code in a way that shares two of the bits. For the other NAA types, the manufacturer ID either comes directly after the NAA code or starts at the third byte. The remaining portion of the WWN is used for vendor-specific information.

For example, the following WWN conforms to the registered format (format 5):

5A:CD:E4:82:34:56:78:98

The WWN includes the manufacturer ID (ACDE48), which directly follows the NAA code (5). The remaining part of the WWN, 234567898, is a vendor-specific identifier. (This example comes from the IEEE.)

There are two types of WWNs that are implemented in a FC Storage Area Network (SAN):

• World Wide Node Name (WWNN). Identifies an FC host bus adapter (HBA) or storage adapter.
• World Wide Port Name (WWPN). Identifies an individual node port on an adapter.

For example, a host might include an HBA that contains two ports, in which case, three WWNs will be associated with that host: one for the HBA itself and two for the ports. However, whether a WWN is a WWNN or a WWPN, the format is the same.

WWNs represent an important part of identifying components when setting up a SAN. Each device must be registered with the SAN by its WWN before the SAN will recognize it. (In fact, if the SAN has trouble recognizing a device, the WWN registration is usually one of the first things an administrator will check.)

In conjunction with the port WWN, a FC network also issues the 24-bit FC identifier (FCID). The FCID facilitates network communications between nodes. When a port logs into the SAN and establishes a connection, the network identifies the port through its WWPN and then dynamically assigns an FCID to that port. The FCID is then used along with other FCIDs to route frames across the network.

See also: SAN switch, Fibre Channel over Ethernet, Fibre Channel director, Fibre Channel adapter, Fibre Channel port names, Fibre Channel Arbitrated Loop and NVMe over Fibre Channel.