Binary Labels in the Domain Name System (RFC2673)
Original Publication Date: 1999-Aug-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
Status of this Memo
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
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.
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 ...