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General Network Working Group This document specifies several RFC numbers of various lengths for which RFCs have never been and should never be issued. These RFC numbers may be useful in testing of or use as example in documentation and referencing systems.

Introduction The RFC Series (ISSN 2070-1721, ) contains technical and organizational documents about the Internet, including the specifications and policy documents produced by several streams, currently the following five: the Internet Engineering Task Force (IETF), the Internet Research Task Force (IRTF), the Internet Architecture Board (IAB), Independent Submissions, and Editorial. It was begun before the IETF was formed. Each RFC is assigned a unique number and these number are not reused. (An RFC is replaced by issuing a new RFC with a new number that obsoletes the RFC being replaced.) RFC numbers are widely used in IETF doocumentation and are frequently referred to or displayed. Current systems are adapted for RFC numbers up to four digits ("9999") but RFC numbers will soon overflow to 5 digits. A five-digit example number that can be used for testing such systems and for use in documentation if needed. Test / example RFC numbers of shorter lengths may also be useful and, conveniently enough, there exist 2-, 3-, and 4- digit RFC numbers that have never been issued and, under current policies, never will be issued. Note that a system tested only with the currently common 4-digit RFC numbers might have difficulty with shorter as well as long RFC numbers. For example, in any such system, there are questions of whether to pad with leading zeros to some fixed length or the like. These considerations have some overlap with those noted in and , which point out that the use of designated code values reserved for documentation and examples reduces the likelihood of conflicts and confusion arising from such code points conflicting with code points assigned for some actual use. The idea of reserved RFC numbers for these purposes was suggested by Brian E. Carpenter.

The Reserved RFC Numbers The reserved RFC numbers that are available for use in testing and experimentation with systems that process or use RFC numbers are show below. These numbers were chosen as the smallest unused number of each length that had not been issued and which, to minimize the likelihood of errors, did not include any zeros or multiple occurrences of the same digit.

Length	RFC Number
1	none available
2	14
3	159
4	1839
5	12345

IANA Considerations This document requires no IANA actions.

Security Considerations TBD

Normative References Informative References RFC Editor

Acknowledgements The idea behind this document was originated by Brian Carpenter. The suggestions and comments of the following persons are gratefully acknowledged: TBD.