Hextets

Hextet is a term used to denote a 16-bit unit in several technical contexts, most prominently in the addressing scheme of IPv6. A hextet consists of four hexadecimal digits and represents values from 0000 to FFFF (0 to 65535). In IPv6 addressing, the 128-bit address is divided into eight consecutive hextets separated by colons.

In an IPv6 address, the eight hextets are arranged in a fixed sequence to convey routing and interface information. For example, the address 2001:0db8:85a3:0000:0000:8a2e:0370:7334 is composed of eight 16-bit hextets. Each hextet encodes a portion of the total address and can be interpreted as part of a global route, a site-local segment, or an interface identifier, depending on its position within the address.

Notation and formatting rules for hextets are designed for readability and compactness. Hextets are written using hexadecimal digits, case-insensitive, with leading zeros within a hextet optionally omitted (e.g., 0db8 can be written as db8). IPv6 addresses may also employ zero compression, where consecutive all-zero hextets are replaced by a double colon (::) once in an address, to shorten the representation.

Etymology and usage context: the term hextet combines hex (base-16) with tet (a four-unit group, reflecting the four hexadecimal digits per field). While common in IPv6 documentation, some texts refer to these units more generally as groups or fields. The concept of a 16-bit field is central to IPv6 addressing but is not limited to this single application.