< draft-ietf-dnsind-serial-01.txt		draft-ietf-dnsind-serial-02.txt >
	Network Working Group Robert Elz		Network Working Group Robert Elz
	Internet Draft University of Melbourne		Internet Draft University of Melbourne
	Expiration Date: August 1996		Expiration Date: September 1996
	Randy Bush		Randy Bush
	RGnet, Inc.		RGnet, Inc.
	February 1996		March 1996
	Serial Number Arithmetic		Serial Number Arithmetic
	draft-ietf-dnsind-serial-01.txt		draft-ietf-dnsind-serial-02.txt
	1. Status of this Memo		1. Status of this Memo
	This document is an Internet-Draft. Internet-Drafts are working		This document is an Internet-Draft. Internet-Drafts are working
	documents of the Internet Engineering Task Force (IETF), its areas,		documents of the Internet Engineering Task Force (IETF), its areas,
	and its working groups. Note that other groups may also distribute		and its working groups. Note that other groups may also distribute
	working documents as Internet-Drafts.		working documents as Internet-Drafts.
	Internet-Drafts are draft documents valid for a maximum of six months		Internet-Drafts are draft documents valid for a maximum of six months
	and may be updated, replaced, or obsoleted by other documents at any		and may be updated, replaced, or obsoleted by other documents at any
	skipping to change at page 2, line 25 ¶		skipping to change at page 2, line 25 ¶
	RFC1034 uses the same terminology when defining secondary server zone		RFC1034 uses the same terminology when defining secondary server zone
	consistency procedures.		consistency procedures.
	Unfortunately the term "sequence space arithmetic" is not defined in		Unfortunately the term "sequence space arithmetic" is not defined in
	either RFC1034 or RFC1035, nor do any of their references provide		either RFC1034 or RFC1035, nor do any of their references provide
	further information.		further information.
	This phrase seems to have been intending to specify arithmetic as		This phrase seems to have been intending to specify arithmetic as
	used in TCP sequence numbers [RFC793], and defined in [IEN-74].		used in TCP sequence numbers [RFC793], and defined in [IEN-74].
	[Aside: there may be another ref, not an IETF (online) doc,
	which may be more to the point, but what is it?]
	Unfortunately, the arithmetic defined in [IEN-74] is not adequate for		Unfortunately, the arithmetic defined in [IEN-74] is not adequate for
	the purposes of the DNS, as no general comparison operator is		the purposes of the DNS, as no general comparison operator is
	defined.		defined.
	To avoid further problems with this simple field, this document		To avoid further problems with this simple field, this document
	defines the field and the operations available upon it. This		defines the field and the operations available upon it. This
	definition is intended merely to clarify the intent of RFC1034 and		definition is intended merely to clarify the intent of RFC1034 and
	RFC1035, and is believed to generally agree with current		RFC1035, and is believed to generally agree with current
	implementations. However, older, superseded, implementations are		implementations. However, older, superseded, implementations are
	known to have treated the serial number as a simple unsigned integer,		known to have treated the serial number as a simple unsigned integer,
	skipping to change at page 5, line 43 ¶		skipping to change at page 5, line 33 ¶
	7. Examples		7. Examples
	7.1. A trivial example		7.1. A trivial example
	The simplest meaningful serial number space has SERIAL_BITS == 2. In		The simplest meaningful serial number space has SERIAL_BITS == 2. In
	this space, the integers that make up the serial number space are 0,		this space, the integers that make up the serial number space are 0,
	1, 2, and 3. That is, 3 == 2^SERIAL_BITS - 1.		1, 2, and 3. That is, 3 == 2^SERIAL_BITS - 1.
	In this space, the largest integer that it is meaningful to add to a		In this space, the largest integer that it is meaningful to add to a
	sequence number is 2^(SERIAL_BITS - 1) - 1, ie: 1.		sequence number is 2^(SERIAL_BITS - 1) - 1, or 1.
	Then, as defined 0+1 == 1, 1+1 == 2, 2+1 == 3, and 3+1 == 0.		Then, as defined 0+1 == 1, 1+1 == 2, 2+1 == 3, and 3+1 == 0.
	Further, 1 > 0, 2 > 1, 3 > 2, and 0 > 3. It is undefined whether		Further, 1 > 0, 2 > 1, 3 > 2, and 0 > 3. It is undefined whether
	2 > 0 or 0 > 2, and whether 1 > 3 or 3 > 1.		2 > 0 or 0 > 2, and whether 1 > 3 or 3 > 1.
	7.2. A slightly larger example		7.2. A slightly larger example
	Consider the case where SERIAL_BITS == 8. In this space the integers		Consider the case where SERIAL_BITS == 8. In this space the integers
	that make up the serial number space are 0, 1, 2, ... 254, 255.		that make up the serial number space are 0, 1, 2, ... 254, 255.
	255 == 2^SERIAL_BITS - 1.		255 == 2^SERIAL_BITS - 1.
	In this space, the largest integer that it is meaningful to add to a		In this space, the largest integer that it is meaningful to add to a
	sequence number is 2^(SERIAL_BITS - 1) - 1, ie: 127.		sequence number is 2^(SERIAL_BITS - 1) - 1, or 127.
	Addition is as expected in this space, eg: 255+1 == 0,		Addition is as expected in this space, for example: 255+1 == 0,
	100+100 == 200, and 200+100 == 44.		100+100 == 200, and 200+100 == 44.
	Comparison is more interesting, 1 > 0, 44 > 0, 100 > 0, 100 > 44,		Comparison is more interesting, 1 > 0, 44 > 0, 100 > 0, 100 > 44,
	200 > 100, 255 > 200, 0 > 255, 100 > 255, 0 > 200, and 44 > 200.		200 > 100, 255 > 200, 0 > 255, 100 > 255, 0 > 200, and 44 > 200.
	Note that 100+100 > 100, but that (100+100)+100 < 100. Incrementing		Note that 100+100 > 100, but that (100+100)+100 < 100. Incrementing
	a serial number can cause it to become "smaller". Of course,		a serial number can cause it to become "smaller". Of course,
	incrementing by a smaller number will allow many more increments to		incrementing by a smaller number will allow many more increments to
	be made before this occurs. However this is always something to be		be made before this occurs. However this is always something to be
	aware of, it can cause surprising errors, or be useful as it is the		aware of, it can cause surprising errors, or be useful as it is the
	skipping to change at page 7, line 32 ¶		skipping to change at page 7, line 9 ¶
	correctly succeeded in following the primary server's serial number		correctly succeeded in following the primary server's serial number
	changes, at each step.		changes, at each step.
	Note that each, and every, increment to the serial number must be		Note that each, and every, increment to the serial number must be
	treated as the start of a new sequence of increments for this		treated as the start of a new sequence of increments for this
	purpose, as well as being the continuation of all previous sequences		purpose, as well as being the continuation of all previous sequences
	started within the period specified by SOA.expire.		started within the period specified by SOA.expire.
	Caution should also be exercised before causing the serial number to		Caution should also be exercised before causing the serial number to
	be set to the value zero. While this value is not in any way special		be set to the value zero. While this value is not in any way special
	in serial number arithmetic, many DNS implementations have treated		in serial number arithmetic, or to the DNS SOA serial number, many
	zero as a special case, with special properties, and unusual		DNS implementations have incorrectly treated zero as a special case,
	behaviour may be expected if zero is used as a DNS SOA serial number.		with special properties, and unusual behaviour may be expected if
			zero is used as a DNS SOA serial number.
	10. Document Updates		10. Document Updates
	RFC1034 and RFC1035 are to be treated as if the references to		RFC1034 and RFC1035 are to be treated as if the references to
	"sequence space arithmetic" therein are replaced by references to		"sequence space arithmetic" therein are replaced by references to
	serial number arithmetic, as defined in this document.		serial number arithmetic, as defined in this document.
	11. Security Considerations		11. Security Considerations
	This document does not consider security.		This document does not consider security.
	skipping to change at page 8, line 30 ¶		skipping to change at page 8, line 8 ¶
	[RFC793] Transmission Control protocol		[RFC793] Transmission Control protocol
	Information Sciences Institute, USC, September 1981		Information Sciences Institute, USC, September 1981
	[IEN-74] Sequence Number Arithmetic		[IEN-74] Sequence Number Arithmetic
	William W. Plummer, BB&N Inc, September 1978		William W. Plummer, BB&N Inc, September 1978
	13. Acknowledgements		13. Acknowledgements
	Thanks to Rob Austein for suggesting clarification of the undefined		Thanks to Rob Austein for suggesting clarification of the undefined
	comparison operators, and to Michael Paddon for attempting to locate		comparison operators, and to Michael Patton for attempting to locate
	the missing reference, which must exist somewhere. Thanks also to		another reference for this procedure. Thanks also to members of the
	members of the IETF DNSIND working group of 1995-6.		IETF DNSIND working group of 1995-6, in particular, Paul Mockapetris.
			14. Author's Address
			Robert Elz
			Computer Science
			University of Melbourne
			Parkville, Vic,
			Australia.
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