World Wide Name - Formats

Formats

Each WWN is an 8 or 16 byte number, the length and format of which is determined by the most significant four bits, which are referred to as an NAA (Network Address Authority.) The remainder of the value is derived from an IEEE OUI (often the term "Company Identifier" is used as a synonym for OUI) and vendor-supplied information. Each format defines a different way to arrange and/or interpret these components. OUIs are used with the U/L and multicast bits zeroed, or sometimes even omitted (and assumed zero.)

The WWN formats include:

• "Original" IEEE formats are essentially a two-byte header followed by an embedded MAC-48/EUI-48 address (which contains the OUI.) The first 2 bytes are either hex 10:00 or 2x:xx (where the x's are vendor-specified) followed by the 3-byte OUI and 3 bytes for a vendor-specified serial number. Thus, the difference between NAA 1 format and NAA 2 format is merely the presence of either a zero pad or an extra 3 nibbles of vendor information.
• "Registered" IEEE formats dispense with padding and place the OUI immediately after the NAA. The OUI is no longer considered to be part of a MAC-48/EUI-48 address. For NAA 5 format, this leaves 9 contiguous nibbles for a vendor-defined value. This is the same format used by the companion NAA 6 format, the only difference being a 16-byte number space is assumed, rather than an 8-byte number space. This leaves a total of 25 contiguous nibbles for vendor-defined values.
• "Mapped EUI-64" formats manage to fit an EUI-64 address into an 8-byte WWN. Since the NAA is mandatory, and takes up a nibble, this represents a four-bit deficit. These four bits are recouped through the following tricks: First, two bits are stolen from the NAA by allocating NAAs 12, 13, 14, and 15 to all refer to the same format. Second, the remaining two bits are recouped by omitting the U/L and multicast bits from the EUI-64's OUI. When reconstructing the embedded EUI-64 value, the U/L and multicast bits are assumed to have carried zero values.