Serial Number Arithmetic (RFC1982)
Original Publication Date: 1996-Aug-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
This memo defines serial number arithmetic, as used in the Domain Name System. The DNS has long relied upon serial number arithmetic, a concept which has never really been defined, certainly not in an IETF document, though which has been widely understood. This memo supplies the missing definition. It is intended to update RFC1034 and RFC1035.
Network Working Group R. Elz
Request for Comments: 1982 University of Melbourne
Updates: 1034, 1035 R. Bush
Category: Standards Track RGnet, Inc.
Serial Number Arithmetic
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.
This memo defines serial number arithmetic, as used in the Domain
Name System. The DNS has long relied upon serial number arithmetic,
a concept which has never really been defined, certainly not in an
IETF document, though which has been widely understood. This memo
supplies the missing definition. It is intended to update RFC1034
The serial number field of the SOA resource record is defined in
SERIAL The unsigned 32 bit version number of the original copy of
the zone. Zone transfers preserve this value. This value
wraps and should be compared using sequence space
RFC1034 uses the same terminology when defining secondary server zone
Unfortunately the term "sequence space arithmetic" is not defined in
either RFC1034 or RFC1035, nor do any of their references provide
This phrase seems to have been intending to specify arithmetic as
used in TCP sequence numbers [RFC793], and defined in [IEN-74].
Unfortunately, the arithmetic defined in [IEN-74] is not adequate for
the purposes of the DNS, as no general comparison operator is
To avoid further problems with this simple field, this document
defines the field and the operations available upon it. This
definition is intended merely to clarify the intent of RFC1034 and
RFC1035, and is believed to generally agree with current
implementations. However, older, superseded, implementations are
known to have treated the serial number as a simple unsigned integer,
with no attempt to implement any kind of "sequence space arithmetic",
however that may have been interpreted, and further, ignoring the
requirement that the value wraps. Nothing can be done with these
implementations, beyond extermination.
2. Serial Number Arithmetic
Serial numbers are formed from non-negative integers from a finite
subset of the range of all integer values. The lowest integer in
every subset used for this purpose is zero, the maximum is always one
less than a power of two.
When considered as serial numbers however no value has any particular