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diff --git a/contrib/bind9/doc/rfc/rfc1982.txt b/contrib/bind9/doc/rfc/rfc1982.txt deleted file mode 100644 index 5a34bc4..0000000 --- a/contrib/bind9/doc/rfc/rfc1982.txt +++ /dev/null @@ -1,394 +0,0 @@ - - - - - - -Network Working Group R. Elz -Request for Comments: 1982 University of Melbourne -Updates: 1034, 1035 R. Bush -Category: Standards Track RGnet, Inc. - August 1996 - - - 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. - -Abstract - - 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. - -1. Introduction - - The serial number field of the SOA resource record is defined in - RFC1035 as - - 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 - arithmetic. - - RFC1034 uses the same terminology when defining secondary server zone - consistency procedures. - - Unfortunately the term "sequence space arithmetic" is not defined in - either RFC1034 or RFC1035, nor do any of their references provide - further information. - - 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 - - - -Elz & Bush Standards Track [Page 1] - -RFC 1982 Serial Number Arithmetic August 1996 - - - defined. - - 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 However, older, superseded, implementations are - known to have treated the serial number as a simple unsigned integer, - with no attempt to implement any kind of "sequence space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 - significance, there is no minimum or maximum serial number, every - value has a successor and predecessor. - - To define a serial number to be used in this way, the size of the - serial number space must be given. This value, called "SERIAL_BITS", - gives the power of two which results in one larger than the largest - integer corresponding to a serial number value. This also specifies - the number of bits required to hold every possible value of a serial - number of the defined type. The operations permitted upon serial - numbers are defined in the following section. - -3. Operations upon the serial number - - Only two operations are defined upon serial numbers, addition of a - positive integer of limited range, and comparison with another serial - number. - -3.1. Addition - - Serial numbers may be incremented by the addition of a positive - integer n, where n is taken from the range of integers - [0 .. (2^(SERIAL_BITS - 1) - 1)]. For a sequence number s, the - result of such an addition, s', is defined as - - s' = (s + n) modulo (2 ^ SERIAL_BITS) - - - - - -Elz & Bush Standards Track [Page 2] - -RFC 1982 Serial Number Arithmetic August 1996 - - - where the addition and modulus operations here act upon values that - are non-negative values of unbounded size in the usual ways of - integer arithmetic. - - Addition of a value outside the range - [0 .. (2^(SERIAL_BITS - 1) - 1)] is undefined. - -3.2. Comparison - - Any two serial numbers, s1 and s2, may be compared. The definition - of the result of this comparison is as follows. - - For the purposes of this definition, consider two integers, i1 and - i2, from the unbounded set of non-negative integers, such that i1 and - s1 have the same numeric value, as do i2 and s2. Arithmetic and - comparisons applied to i1 and i2 use ordinary unbounded integer - arithmetic. - - Then, s1 is said to be equal to s2 if and only if i1 is equal to i2, - in all other cases, s1 is not equal to s2. - - s1 is said to be less than s2 if, and only if, s1 is not equal to s2, - and - - (i1 < i2 and i2 - i1 < 2^(SERIAL_BITS - 1)) or - (i1 > i2 and i1 - i2 > 2^(SERIAL_BITS - 1)) - - s1 is said to be greater than s2 if, and only if, s1 is not equal to - s2, and - - (i1 < i2 and i2 - i1 > 2^(SERIAL_BITS - 1)) or - (i1 > i2 and i1 - i2 < 2^(SERIAL_BITS - 1)) - - Note that there are some pairs of values s1 and s2 for which s1 is - not equal to s2, but for which s1 is neither greater than, nor less - than, s2. An attempt to use these ordering operators on such pairs - of values produces an undefined result. - - The reason for this is that those pairs of values are such that any - simple definition that were to define s1 to be less than s2 where - (s1, s2) is such a pair, would also usually cause s2 to be less than - s1, when the pair is (s2, s1). This would mean that the particular - order selected for a test could cause the result to differ, leading - to unpredictable implementations. - - While it would be possible to define the test in such a way that the - inequality would not have this surprising property, while being - defined for all pairs of values, such a definition would be - - - -Elz & Bush Standards Track [Page 3] - -RFC 1982 Serial Number Arithmetic August 1996 - - - unnecessarily burdensome to implement, and difficult to understand, - and would still allow cases where - - s1 < s2 and (s1 + 1) > (s2 + 1) - - which is just as non-intuitive. - - Thus the problem case is left undefined, implementations are free to - return either result, or to flag an error, and users must take care - not to depend on any particular outcome. Usually this will mean - avoiding allowing those particular pairs of numbers to co-exist. - - The relationships greater than or equal to, and less than or equal - to, follow in the natural way from the above definitions. - -4. Corollaries - - These definitions give rise to some results of note. - -4.1. Corollary 1 - - For any sequence number s and any integer n such that addition of n - to s is well defined, (s + n) >= s. Further (s + n) == s only when - n == 0, in all other defined cases, (s + n) > s. - -4.2. Corollary 2 - - If s' is the result of adding the non-zero integer n to the sequence - number s, and m is another integer from the range defined as able to - be added to a sequence number, and s" is the result of adding m to - s', then it is undefined whether s" is greater than, or less than s, - though it is known that s" is not equal to s. - -4.3. Corollary 3 - - If s" from the previous corollary is further incremented, then there - is no longer any known relationship between the result and s. - -4.4. Corollary 4 - - If in corollary 2 the value (n + m) is such that addition of the sum - to sequence number s would produce a defined result, then corollary 1 - applies, and s" is known to be greater than s. - - - - - - - - -Elz & Bush Standards Track [Page 4] - -RFC 1982 Serial Number Arithmetic August 1996 - - -5. Examples - -5.1. A trivial example - - The simplest meaningful serial number space has SERIAL_BITS == 2. In - this space, the integers that make up the serial number space are 0, - 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 - 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. - 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. - -5.2. A slightly larger example - - 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. - 255 == 2^SERIAL_BITS - 1. - - In this space, the largest integer that it is meaningful to add to a - sequence number is 2^(SERIAL_BITS - 1) - 1, or 127. - - Addition is as expected in this space, for example: 255+1 == 0, - 100+100 == 200, and 200+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. - - Note that 100+100 > 100, but that (100+100)+100 < 100. Incrementing - a serial number can cause it to become "smaller". Of course, - incrementing by a smaller number will allow many more increments to - 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 - only defined way to actually cause a serial number to decrease. - - The pairs of values 0 and 128, 1 and 129, 2 and 130, etc, to 127 and - 255 are not equal, but in each pair, neither number is defined as - being greater than, or less than, the other. - - It could be defined (arbitrarily) that 128 > 0, 129 > 1, - 130 > 2, ..., 255 > 127, by changing the comparison operator - definitions, as mentioned above. However note that that would cause - 255 > 127, while (255 + 1) < (127 + 1), as 0 < 128. Such a - definition, apart from being arbitrary, would also be more costly to - implement. - - - - -Elz & Bush Standards Track [Page 5] - -RFC 1982 Serial Number Arithmetic August 1996 - - -6. Citation - - As this defined arithmetic may be useful for purposes other than for - the DNS serial number, it may be referenced as Serial Number - Arithmetic from RFC1982. Any such reference shall be taken as - implying that the rules of sections 2 to 5 of this document apply to - the stated values. - -7. The DNS SOA serial number - - The serial number in the DNS SOA Resource Record is a Serial Number - as defined above, with SERIAL_BITS being 32. That is, the serial - number is a non negative integer with values taken from the range - [0 .. 4294967295]. That is, a 32 bit unsigned integer. - - The maximum defined increment is 2147483647 (2^31 - 1). - - Care should be taken that the serial number not be incremented, in - one or more steps, by more than this maximum within the period given - by the value of SOA.expire. Doing so may leave some secondary - servers with out of date copies of the zone, but with a serial number - "greater" than that of the primary server. Of course, special - circumstances may require this rule be set aside, for example, when - the serial number needs to be set lower for some reason. If this - must be done, then take special care to verify that ALL servers have - correctly succeeded in following the primary server's serial number - changes, at each step. - - Note that each, and every, increment to the serial number must be - treated as the start of a new sequence of increments for this - purpose, as well as being the continuation of all previous sequences - started within the period specified by SOA.expire. - - 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 - in serial number arithmetic, or to the DNS SOA serial number, many - DNS implementations have incorrectly treated zero as a special case, - with special properties, and unusual behaviour may be expected if - zero is used as a DNS SOA serial number. - - - - - - - - - - - - -Elz & Bush Standards Track [Page 6] - -RFC 1982 Serial Number Arithmetic August 1996 - - -8. Document Updates - - RFC1034 and RFC1035 are to be treated as if the references to - "sequence space arithmetic" therein are replaced by references to - serial number arithmetic, as defined in this document. - -9. Security Considerations - - This document does not consider security. - - It is not believed that anything in this document adds to any - security issues that may exist with the DNS, nor does it do anything - to lessen them. - -References - - [RFC1034] Domain Names - Concepts and Facilities, - P. Mockapetris, STD 13, ISI, November 1987. - - [RFC1035] Domain Names - Implementation and Specification - P. Mockapetris, STD 13, ISI, November 1987 - - [RFC793] Transmission Control protocol - Information Sciences Institute, STD 7, USC, September 1981 - - [IEN-74] Sequence Number Arithmetic - William W. Plummer, BB&N Inc, September 1978 - -Acknowledgements - - Thanks to Rob Austein for suggesting clarification of the undefined - comparison operators, and to Michael Patton for attempting to locate - another reference for this procedure. Thanks also to members of the - IETF DNSIND working group of 1995-6, in particular, Paul Mockapetris. - -Authors' Addresses - - Robert Elz Randy Bush - Computer Science RGnet, Inc. - University of Melbourne 10361 NE Sasquatch Lane - Parkville, Vic, 3052 Bainbridge Island, Washington, 98110 - Australia. United States. - - EMail: kre@munnari.OZ.AU EMail: randy@psg.com - - - - - - - -Elz & Bush Standards Track [Page 7] |
