Binary Labels in the Domain Name System (RFC2673)
Original Publication Date: 1999-Aug-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
This document defines a "Bit-String Label" which may appear within domain names. This new label type compactly represents a sequence of "One-Bit Labels" and enables resource records to be stored at any bit- boundary in a binary-named section of the domain name tree. [STANDARDS-TRACK]
Network Working Group M. Crawford Request for Comments: 2673 Fermilab Category: Standards Track August 1999
Binary Labels in the Domain Name System
Status of this Memo
This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1999). All Rights Reserved.
1. Introduction and Terminology
This document defines a "Bit-String Label" which may appear within domain names. This new label type compactly represents a sequence of "One-Bit Labels" and enables resource records to be stored at any bit-boundary in a binary-named section of the domain name tree.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [KWORD].
Binary labels are intended to efficiently solve the problem of storing data and delegating authority on arbitrary boundaries when the structure of underlying name space is most naturally represented in binary.
3. Label Format
Up to 256 One-Bit Labels can be grouped into a single Bit-String Label. Within a Bit-String Label the most significant or "highest level" bit appears first. This is unlike the ordering of DNS labels themselves, which has the least significant or "lowest level" label first. Nonetheless, this ordering seems to be the most natural and efficient for representing binary labels.
Crawford Standards Track [Page 1]
RFC 2673 Binary Labels in the Domain Name System August 1999
Among consecutive Bit-String Labels, the bits in the first-appearing label are less significant or "at a lower level" than the bits in subsequent Bit-String Labels, just as ASCII labels are ordered.
0 1 2 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-//+-+-+-+-+-+-+ |0 1| ELT | Count | Label ... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+//-+-+-+-+-+-+-+
(Each tic mark represents one bit.)
ELT 000001 binary, the six-bit extended label type [EDNS0] assigned to the Bit-String Label.
Count The number of significant bits in the Label field. A Count value of zero indicates that 256 bits are significant. (Thus the null label representing the DNS root cannot be represented as a Bit String Label.)
Label The bit string representing a sequence of One-Bit Labels, with the most significant bit first. That is, the One-Bit Label in position 17 in the diagram above represents a subdomain of the domain represented by the One-Bit Label in position 16, and so on.
The Label field is padded on the right with zero to seven pad bits to make the entire field occupy an integral number of octets. These pad bits MUST be zero on transmission an...