Linux uses WWN to identify disks by providing symbolic links to the real device entry: However, there is much variance between vendors. WWN addresses are predominantly represented as colon separated hexadecimal octets, MSB-first, with leading zeros - similar to Ethernet's MAC address.
When reconstructing the embedded EUI-64 value, the U/L and multicast bits are assumed to have carried zero values. Second, the remaining two bits are recouped by omitting the U/L and multicast bits from the EUI-64's OUI. 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. Since the NAA is mandatory, and takes up a nibble, this represents a four-bit deficit. "Mapped EUI-64" formats manage to fit an EUI-64 address into an 8-byte WWN.This leaves a total of 25 contiguous nibbles for vendor-defined values. 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. For NAA 5 format, this leaves 9 contiguous nibbles for a vendor-defined value. The OUI is no longer considered to be part of a EUI-48 address. "Registered" IEEE formats dispense with padding and place the OUI immediately after the NAA.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. 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.
"Original" IEEE formats are essentially a two-byte header followed by an embedded EUI-48 address (which contains the OUI).OUIs are used with the U/L and multicast bits zeroed, or sometimes even omitted (and assumed zero). Each format defines a different way to arrange and/or interpret these components. The remainder of the value is derived from an IEEE OUI (or from Company Id (CID)) and vendor-supplied information. 5 List of OUIs commonly seen as WWN Company IdentifiersĮach 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).
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