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Versions: (draft-kawamura-ipv6-text-representation) 00 01 02 03 04 05 06 07 RFC 5952

IPv6 Maintenance Working Group                               S. Kawamura
Internet-Draft                                         NEC BIGLOBE, Ltd.
Intended status: Standards Track                            M. Kawashima
Expires: July 18, 2010                          NEC AccessTechnica, Ltd.
                                                        January 14, 2010


         A Recommendation for IPv6 Address Text Representation
              draft-ietf-6man-text-addr-representation-04

Abstract

   As IPv6 network grows, there will be more engineers and also non-
   engineers who will have the need to use an IPv6 address in text.
   While the IPv6 address architecture RFC 4291 section 2.2 depicts a
   flexible model for text representation of an IPv6 address, this
   flexibility has been causing problems for operators, system
   engineers, and users.  This document will describe the problems that
   a flexible text representation has been causing.  This document also
   recommends a canonical representation format that best avoids
   confusion.  It is expected that the canonical format is followed by
   humans and systems when representing IPv6 addresses as text, but all
   implementations must accept and be able to handle any legitimate
   RFC4291 format.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   This Internet-Draft will expire on July 18, 2010.




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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  Requirements Language  . . . . . . . . . . . . . . . . . .  4
   2.  Text Representation Flexibility of RFC4291 . . . . . . . . . .  4
     2.1.  Leading Zeros in a 16 Bit Field  . . . . . . . . . . . . .  4
     2.2.  Zero Compression . . . . . . . . . . . . . . . . . . . . .  5
     2.3.  Uppercase or Lowercase . . . . . . . . . . . . . . . . . .  5
   3.  Problems Encountered with the Flexible Model . . . . . . . . .  6
     3.1.  Searching  . . . . . . . . . . . . . . . . . . . . . . . .  6
       3.1.1.  General Summary  . . . . . . . . . . . . . . . . . . .  6
       3.1.2.  Searching Spreadsheets and Text Files  . . . . . . . .  6
       3.1.3.  Searching with Whois . . . . . . . . . . . . . . . . .  6
       3.1.4.  Searching for an Address in a Network Diagram  . . . .  7
     3.2.  Parsing and Modifying  . . . . . . . . . . . . . . . . . .  7
       3.2.1.  General Summary  . . . . . . . . . . . . . . . . . . .  7
       3.2.2.  Logging  . . . . . . . . . . . . . . . . . . . . . . .  7
       3.2.3.  Auditing: Case 1 . . . . . . . . . . . . . . . . . . .  7
       3.2.4.  Auditing: Case 2 . . . . . . . . . . . . . . . . . . .  8
       3.2.5.  Verification . . . . . . . . . . . . . . . . . . . . .  8
       3.2.6.  Unexpected Modifying . . . . . . . . . . . . . . . . .  8
     3.3.  Operating  . . . . . . . . . . . . . . . . . . . . . . . .  8
       3.3.1.  General Summary  . . . . . . . . . . . . . . . . . . .  8
       3.3.2.  Customer Calls . . . . . . . . . . . . . . . . . . . .  8
       3.3.3.  Abuse  . . . . . . . . . . . . . . . . . . . . . . . .  9
     3.4.  Other Minor Problems . . . . . . . . . . . . . . . . . . .  9
       3.4.1.  Changing Platforms . . . . . . . . . . . . . . . . . .  9
       3.4.2.  Preference in Documentation  . . . . . . . . . . . . .  9
       3.4.3.  Legibility . . . . . . . . . . . . . . . . . . . . . .  9
   4.  A Recommendation for IPv6 Text Representation  . . . . . . . .  9
     4.1.  Handling Leading Zeros in a 16 Bit Field . . . . . . . . . 10
     4.2.  "::" Usage . . . . . . . . . . . . . . . . . . . . . . . . 10



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       4.2.1.  Shorten As Much As Possible  . . . . . . . . . . . . . 10
       4.2.2.  Handling One 16 Bit 0 Field  . . . . . . . . . . . . . 10
       4.2.3.  Choice in Placement of "::"  . . . . . . . . . . . . . 10
     4.3.  Lower Case . . . . . . . . . . . . . . . . . . . . . . . . 10
   5.  Text Representation of Special Addresses . . . . . . . . . . . 10
   6.  Notes on Combining IPv6 Addresses with Port Numbers  . . . . . 11
   7.  Prefix Representation  . . . . . . . . . . . . . . . . . . . . 11
   8.  Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 13
     12.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Appendix A.  For Developers  . . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13



































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1.  Introduction

   A single IPv6 address can be text represented in many ways.  Examples
   are shown below.

      2001:db8:0:0:1:0:0:1

      2001:0db8:0:0:1:0:0:1

      2001:db8::1:0:0:1

      2001:db8::0:1:0:0:1

      2001:0db8::1:0:0:1

      2001:db8:0:0:1::1

      2001:db8:0000:0:1::1

      2001:DB8:0:0:1::1

   All the above point to the same IPv6 address.  This flexibility has
   caused many problems for operators, systems engineers, and customers.
   The problems will be noted in Section 3.  Also, a canonical
   representation format to avoid problems will be introduced in
   Section 4.

1.1.  Requirements Language

   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 [RFC2119].


2.  Text Representation Flexibility of RFC4291

   Examples of flexibility in Section 2.2 of [RFC4291] are described
   below.

2.1.  Leading Zeros in a 16 Bit Field

      'It is not necessary to write the leading zeros in an individual
      field.'

   In other words, it is also not necessary to omit leading zeros.  This
   means that, it is possible to select from such as the following
   example.  The final 16 bit field is different, but all these
   addresses mean the same.



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      2001:db8:aaaa:bbbb:cccc:dddd:eeee:0001

      2001:db8:aaaa:bbbb:cccc:dddd:eeee:001

      2001:db8:aaaa:bbbb:cccc:dddd:eeee:01

      2001:db8:aaaa:bbbb:cccc:dddd:eeee:1

2.2.  Zero Compression

      'A special syntax is available to compress the zeros.  The use of
      "::" indicates one or more groups of 16 bits of zeros.'

   It is possible to select whether or not to omit just one 16 bits of
   zeros.

      2001:db8:aaaa:bbbb:cccc:dddd::1

      2001:db8:aaaa:bbbb:cccc:dddd:0:1

   In case where there are more than one zero fields, there is a choice
   of how many fields can be shortened.  Examples follow.

      2001:db8:0:0:0::1

      2001:db8:0:0::1

      2001:db8:0::1

      2001:db8::1

   In addition, [RFC4291] in section 2.2 notes,

      'The "::" can only appear once in an address.'

   This gives a choice on where, in a single address to compress the
   zero.  Examples are shown below.

      2001:db8::aaaa:0:0:1

      2001:db8:0:0:aaaa::1

2.3.  Uppercase or Lowercase

   [RFC4291] does not mention about preference of uppercase or
   lowercase.  Various flavors are shown below.





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      2001:db8:aaaa:bbbb:cccc:dddd:eeee:aaaa

      2001:db8:aaaa:bbbb:cccc:dddd:eeee:AAAA

      2001:db8:aaaa:bbbb:cccc:dddd:eeee:AaAa


3.  Problems Encountered with the Flexible Model

3.1.  Searching

3.1.1.  General Summary

   A search of an IPv6 address if conducted through a UNIX system is
   usually case sensitive and extended options to allow for regular
   expression use will come in handy.  However, there are many
   applications in the Internet today that do not provide this
   capability.  When searching for an IPv6 address in such systems, the
   system engineer will have to try each and every possibility to search
   for an address.  This has critical impacts especially when trying to
   deploy IPv6 over an enterprise network.

3.1.2.  Searching Spreadsheets and Text Files

   Spreadsheet applications and text editors on GUI systems, rarely have
   the ability to search for a text using regular expression.  Moreover,
   there are many non-engineers (who are not aware of case sensitivity
   and regular expression use) that use these application to manage IP
   addresses.  This has worked quite well with IPv4 since text
   representation in IPv4 has very little flexibility.  There is no
   incentive to encourage these non-engineers to change their tool or
   learn regular expression when they decide to go dual-stack.  If the
   entry in the spreadsheet reads, 2001:db8::1:0:0:1, but the search was
   conducted as 2001:db8:0:0:1::1, this will show a result of no match.
   One example where this will cause problem is, when the search is
   being conducted to assign a new address from a pool, and a check was
   being done to see if it was not in use.  This may cause problems to
   the end-hosts or end-users.  This type of address management is very
   often seen in enterprise networks and also in ISPs.

3.1.3.  Searching with Whois

   The "whois" utility is used by a wide range of people today.  When a
   record is set to a database, one will likely check the output to see
   if the entry is correct.  If an entity was recorded as 2001:db8::/48,
   but the whois output showed 2001:0db8:0000::/48, most non-engineers
   would think that their input was wrong, and will likely retry several
   times or make a frustrated call to the database hostmaster.  If there



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   was a need to register the same address on different systems, and
   each system showed a different text representation, this would
   confuse people even more.  Although this document focuses on
   addresses rather than prefixes, this is worth mentioning since
   problems encountered are mostly equal.

3.1.4.  Searching for an Address in a Network Diagram

   Network diagrams and blue-prints contain IP addresses as allocated to
   system devices.  In times of trouble shooting, there may be a need to
   search through a diagram to find the point of failure (for example,
   if a traceroute stopped at 2001:db8::1, one would search the diagram
   for that address).  This is a technique quite often in use in
   enterprise networks and managed services.  Again, the different
   flavors of text representation will result in a time-consuming
   search, leading to longer MTTR in times of trouble.

3.2.  Parsing and Modifying

3.2.1.  General Summary

   With all the possible text representation ways, each application must
   include a module, object, link, etc. to a function that will parse
   IPv6 addresses in a manner that no matter how it is represented, they
   will mean the same address.  This is not too much a problem if the
   output is to be just 'read' or 'managed' by a network engineer.
   However, many system engineers who integrate complex computer systems
   to corporate customers will have difficulties finding that their
   favorite tool will not have this function, or will encounter
   difficulties such as having to rewrite their macro's or scripts for
   their customers.

3.2.2.  Logging

   If an application were to output a log summary that represented the
   address in full (such as 2001:0db8:0000:0000:1111:2222:3333:4444),
   the output would be highly unreadable compared to the IPv4 output.
   The address would have to be parsed and reformed to make it useful
   for human reading.  Sometimes, logging for critical systems is done
   by mirroring the same traffic to two different systems.  Care must be
   taken that no matter what the log output is, the logs should be
   parsed so they will mean the same.

3.2.3.  Auditing: Case 1

   When a router or any other network appliance machine configuration is
   audited, there are many methods to compare the configuration
   information of a node.  Sometimes, auditing will be done by just



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   comparing the changes made each day.  In this case, if configuration
   was done such that 2001:db8::1 was changed to 2001:0db8:0000:0000:
   0000:0000:0000:0001 just because the new engineer on the block felt
   it was better, a simple diff will tell you that a different address
   was configured.  If this was done on a wide scale network, people
   will be focusing on 'why the extra zeros were put in' instead of
   doing any real auditing.  Lots of tools are just plain 'diff's that
   do not take into account address representation rules.

3.2.4.  Auditing: Case 2

   Node configurations will be matched against an information system
   that manages IP addresses.  If output notation is different, there
   will need to be a script that is implemented to cover for this.  The
   result of an SNMP GET operation, converted to text and compared to a
   textual address written by a human is highly unlikely to match on
   first try.

3.2.5.  Verification

   Some protocols require certain data fields to be verified.  One
   example of this is X.509 certificates.  If an IPv6 address field in a
   certificate was incorrectly verified by converting it to text and
   making a simple textual comparison to some other address, the
   certificate may be mistakenly shown as being invalid due to a
   difference in text representation methods.

3.2.6.  Unexpected Modifying

   Sometimes, a system will take an address and modify it as a
   convenience.  For example, a system may take an input of
   2001:0db8:0::1 and make the output 2001:db8::1.  If the zeros were
   input for a reason, the outcome may be somewhat unexpected.

3.3.  Operating

3.3.1.  General Summary

   When an operator sets an IPv6 address of a system as 2001:db8:0:0:1:
   0:0:1, the system may take the address and show the configuration
   result as 2001:DB8::1:0:0:1.  Someone familiar with IPv6 address
   representation will know that the right address is set, but not
   everyone may understand this.

3.3.2.  Customer Calls

   When a customer calls to inquire about a suspected outage, IPv6
   address representation should be handled with care.  Not all



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   customers are engineers nor have the same skill in IPv6 technology.
   The network operations center will have to take extra steps to
   humanly parse the address to avoid having to explain to the customers
   that 2001:db8:0:1::1 is the same as 2001:db8::1:0:0:0:1.  This is one
   thing that will never happen in IPv4 because IPv4 address cannot be
   abbreviated.

3.3.3.  Abuse

   Network abuse is reported along with the abusing IP address.  This
   'reporting' could take any shape or form of the flexible model.  A
   team that handles network abuse must be able to tell the difference
   between a 2001:db8::1:0:1 and 2001:db8:1::0:1.  Mistakes in the
   placement of the "::" will result in a critical situation.  A system
   that handles these incidents should be able to handle any type of
   input and parse it in a correct manner.  Also, incidents are reported
   over the phone.  It is unnecessary to report if the letter is an
   uppercase or lowercase.  However, when a letter is spelled uppercase,
   people tend to clarify that it is uppercase, which is unnecessary
   information.

3.4.  Other Minor Problems

3.4.1.  Changing Platforms

   When an engineer decides to change the platform of a running service,
   the same code may not work as expected due to the difference in IPv6
   address text representation.  Usually, a change in a platform (e.g.
   Unix to Windows, Cisco to Juniper) will result in a major change of
   code anyway, but flexibility in address representation will increase
   the work load.

3.4.2.  Preference in Documentation

   A document that is edited by more than one author, may become harder
   to read.

3.4.3.  Legibility

   Capital case D and 0 can be quite often misread.  Capital B and 8 can
   also be misread.


4.  A Recommendation for IPv6 Text Representation

   A recommendation for a canonical text representation format of IPv6
   addresses is presented in this section.  The recommendation in this
   document is one that, complies fully with [RFC4291], is implemented



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   by various operating systems, and is human friendly.  The
   recommendation in this document SHOULD be followed by systems when
   generating an address to represent as text, but all implementations
   MUST accept any legitimate [RFC4291] format.  It is advised that
   humans also follow these recommendations when spelling an address.

4.1.  Handling Leading Zeros in a 16 Bit Field

   Leading zeros should be chopped for human legibility and easier
   searching.  Also, a single 16 bit 0000 field should be represented as
   just 0.

4.2.  "::" Usage

4.2.1.  Shorten As Much As Possible

   The use of "::" should be used to its maximum capability (i.e. 2001:
   db8::0:1 is not considered as clean representation).

4.2.2.  Handling One 16 Bit 0 Field

   "::" should not be used to shorten just one 16 bit 0 field for it
   would tend to mislead that there are more than one 16 bit field that
   is shortened.

4.2.3.  Choice in Placement of "::"

   When there is an alternative choice in the placement of a "::", the
   longest run of consecutive 16 bit 0 fields should be shortened (i.e.
   latter is shortened in 2001:0:0:1:0:0:0:1).  When the length of the
   consecutive 16 bit 0 fields are equal (i.e. 2001:db8:0:0:1:0:0:1),
   the former is shortened.  This is consistent with many current
   implementations.  One idea to avoid any confusion, is for the
   operator to not use 16 bit field 0 in the first 64 bits.  By nature
   IPv6 addresses are usually assigned or allocated to end-users from a
   prefix of 32 bits or longer (typically 48 bits or longer).

4.3.  Lower Case

   Recent implementations tend to represent IPv6 address as lower case.
   It is better to use lower case to avoid problems such as described in
   section 3.3.3 and 3.4.3.


5.  Text Representation of Special Addresses

   Addresses such as IPv4-Mapped IPv6 addresses, ISATAP [RFC5214], and
   IPv4-translatable addresses [I-D.ietf-behave-address-format] have



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   IPv4 addresses embedded in the low-order 32 bits of the address.
   These addresses have special representation that may mix hexadecimal
   and dot decimal notations.  The decimal notation may be used only for
   the last 32 bits of the address.  For these addresses, mixed notation
   is recommended if the following condition is met: The address can be
   distinguished as having IPv4 addresses embedded in the lower 32 bits
   solely from the address field through the use of a well known prefix.
   If it is known by some external method that a given prefix includes
   an IPv4 address, it MAY be represented as mixed notation.  Tools that
   provide options to specify prefixes that is (or is not) to be
   represented as mixed notation may be useful.

   The text representation method noted in Section 4 should be applied
   for the leading hexadecimal part (i.e. ::ffff:192.0.2.1 instead of
   0:0:0:0:0:ffff:192.0.2.1).


6.  Notes on Combining IPv6 Addresses with Port Numbers

   When IPv6 addresses and port numbers are represented in text combined
   together, there are many different ways to do so.  Examples are shown
   below.

   o  [2001:db8::1]:80

   o  2001:db8::1:80

   o  2001:db8::1.80

   o  2001:db8::1 port 80

   o  2001:db8::1p80

   o  2001:db8::1#80

   The situation is not much different in IPv4, but the most ambiguous
   case with IPv6 is the second bullet.  This is due to the "::"usage in
   IPv6 addresses.  This style is not recommended for its ambiguity.
   The [] style as expressed in [RFC3986] should be employed, and is the
   default unless otherwise specified.  Other styles are acceptable when
   there is exactly one style for the given context and cross-platform
   portability does not become an issue.


7.  Prefix Representation

   Problems with prefixes are just the same as problems encountered with
   addresses.  Text representation method of IPv6 prefixes should be no



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   different from that of IPv6 addresses.


8.  Conclusion

   The recommended format of text representing an IPv6 address is
   summarized as follows.

      (1) omit leading zeros in a 16 bit field

      (2) when using "::", shorten consecutive zero fields to their
      maximum extent (leave no zero fields behind).

      (3) "::" used where shortens address the most

      (4) "::" used in the former part in case of a tie breaker

      (5) do not shorten one 16 bit 0 field, but always shorten when
      there are two or more consecutive 16 bit 0 fields

      (6) use lower case

   Hints for developers are written in the Appendix section.


9.  Security Considerations

   None.


10.  IANA Considerations

   None.


11.  Acknowledgements

   The authors would like to thank Jan Zorz, Randy Bush, Yuichi Minami,
   Toshimitsu Matsuura for their generous and helpful comments in kick
   starting this document.  We also would like to thank Brian Carpenter,
   Akira Kato, Juergen Schoenwaelder, Antonio Querubin, Dave Thaler,
   Brian Haley, Suresh Krishnan, Jerry Huang, Roman Donchenko, Heikki
   Vatiainen ,Dan Wing for their input.  Also a very special thanks to
   Ron Bonica, Fred Baker, Brian Haberman, Robert Hinden, Jari Arkko,
   and Kurt Lindqvist for their support in bringing this document to the
   light of IETF working groups.





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12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
              Architecture", RFC 4291, February 2006.

12.2.  Informative References

   [I-D.ietf-behave-address-format]
              Huitema, C., Bao, C., Bagnulo, M., Boucadair, M., and X.
              Li, "IPv6 Addressing of IPv4/IPv6 Translators",
              draft-ietf-behave-address-format-03 (work in progress),
              December 2009.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC4038]  Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
              Castro, "Application Aspects of IPv6 Transition",
              RFC 4038, March 2005.

   [RFC5214]  Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
              Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214,
              March 2008.


Appendix A.  For Developers

   We recommend that developers use display routines that conform to
   these rules.  For example, the usage of getnameinfo() with flags
   argument NI_NUMERICHOST in FreeBSD 7.0 will give a conforming output,
   except for the special addresses notes in Section 5.  The function
   inet_ntop() of FreeBSD7.0 is a good C code reference, but should not
   be called directly.  See [RFC4038] for details.












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Authors' Addresses

   Seiichi Kawamura
   NEC BIGLOBE, Ltd.
   14-22, Shibaura 4-chome
   Minatoku, Tokyo  108-8558
   JAPAN

   Phone: +81 3 3798 6085
   Email: kawamucho@mesh.ad.jp


   Masanobu Kawashima
   NEC AccessTechnica, Ltd.
   800, Shimomata
   Kakegawa-shi, Shizuoka  436-8501
   JAPAN

   Phone: +81 537 23 9655
   Email: kawashimam@necat.nec.co.jp































Kawamura & Kawashima      Expires July 18, 2010                [Page 14]


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