A Recommendation for IPv6 Address Text Representation
draft-ietf-6man-text-addr-representation-07

IPv6 Maintenance Working Group S. Kawamura
Internet-Draft NEC BIGLOBE, Ltd.
Updates: 4291 (if approved) M. Kawashima
Intended status: Standards Track NEC AccessTechnica, Ltd.
Expires: August 29, 2010 February 25, 2010
 A Recommendation for IPv6 Address Text Representation
 draft-ietf-6man-text-addr-representation-07
Abstract
 As IPv6 deployment increases there will be a dramatic increase in the
 need to use IPv6 addresses in text. While the IPv6 address
 architecture in RFC 4291 section 2.2 describes a flexible model for
 text representation of an IPv6 address this flexibility has been
 causing problems for operators, system engineers, and users. This
 document defines a canonical textual representation format. It does
 not define a format for internal storage, such as within an
 application or database. 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 RFC 4291 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
 other groups may also distribute working documents as Internet-
 Drafts.
 Internet-Drafts are draft documents valid for a maximum of six months
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 time. It is inappropriate to use Internet-Drafts as reference
 material or to cite them other than as "work in progress."
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 http://www.ietf.org/ietf/1id-abstracts.txt.
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 This Internet-Draft will expire on August 29, 2010.
Copyright Notice
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 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
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 described in the BSD License.
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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
 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 . . . . . . . . . . . . . . . . . . . . 12
 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
 11.1. Normative References . . . . . . . . . . . . . . . . . . . 12
 11.2. 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:.&checktime(0000,0,1,':')::1
 2001:DB8:0:0:1::1
 All of the above examples represent the same IPv6 address. This
 flexibility has caused many problems for operators, systems
 engineers, and customers. The problems are noted in Section 3.
 Also, a canonical representation format to avoid problems is
 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.'
 Conversely 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 represent the same address.
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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 is more than one zero fields, there is a choice
 of how many fields can be shortened.
 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.
 2001:db8::aaaa:0:0:1
 2001:db8:0:0:aaaa::1
2.3. Uppercase or Lowercase
 [RFC4291] does not mention any preference of uppercase or lowercase.
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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 the
 problems encountered are mostly equal.
3.1.4. Searching for an Address in a Network Diagram
 Network diagrams and blueprints often show what IP addresses are
 assigned to a 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 methods of text representation 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. Many system engineers
 who integrate complex computer systems for 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 macros 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 so 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
 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:
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 0000:0000:0000:0001 just because the new engineer on the block felt
 it was better, a simple diff will show 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 diffs 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 the
 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
 customers are engineers nor have the same skill in IPv6 technology.
 The network operations center will have to take extra steps to
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 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 reports generally include 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
 by various operating systems, and is human friendly. The
 recommendation in this section SHOULD be followed by systems when
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 generating an address to represent as text, but all implementations
 MUST accept and be able to handle 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 MUST be suppressed. For example 2001:0db8::0001 is not
 acceptable and must be represented as 2001:db8::1. A single 16 bit
 0000 field MUST be represented as 0.
4.2. "::" Usage
4.2.1. Shorten As Much As Possible
 The use of symbol "::" MUST be used to its maximum capability. For
 example, 2001:db8::0:1 is not acceptable, because the symbol "::"
 could have been used to produce a shorter representation 2001:db8::1.
4.2.2. Handling One 16 Bit 0 Field
 The symbol "::" MUST NOT be used to shorten just one 16 bit 0 field.
 For example, the representation 2001:db8:0:1:1:1:1:1 is correct, but
 2001:db8::1:1:1:1:1 is not correct.
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 MUST be shortened (i.e.
 the sequence with three consecutive zero fields 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 first sequence of zero
 bits MUST be shortened. For example 2001:db8::1:0:0:1 is correct
 representation.
4.3. Lower Case
 The characters "a", "b", "c", "d", "e", "f" in an IPv6 address MUST
 be represented in lower case.
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
 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
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 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.
 Such prefixes are defined in [RFC4291] and [RFC2765] at the time of
 writing. If it is known by some external method that a given prefix
 is used to embed IPv4, it MAY be represented as mixed notation.
 Tools that provide options to specify prefixes that are (or are not)
 to be represented as mixed notation may be useful.
 There is a trade-off here where a recommendation to achieve exact
 match in a search (no dot decimals whatsoever) and recommendation to
 help the readability of an addresses (dot decimal whenever possible)
 does not result in the same solution. The above recommendation is
 aimed at fixing the representation as much as possible while leaving
 the opportunity for future well known prefixes to be represented in a
 human friendly manner as tools adjust to newly assigned prefixes.
 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. For URIs containing IPv6
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 address literals, [RFC3986] MUST be followed, as well as the rules in
 this document.
7. Prefix Representation
 Problems with prefixes are just the same as problems encountered with
 addresses. The text representation method of IPv6 prefixes should be
 no different from that of IPv6 addresses.
8. Security Considerations
 This document notes some examples where IPv6 addresses are compared
 in text format. The example on Section 3.2.5 is one that may cause a
 security risk if used for access control. The common practice of
 comparing X.509 data is done in binary format.
9. IANA Considerations
 None.
10. 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, and Doug Barton 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.
11. References
11.1. Normative References
 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
 Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
 (SIIT)", RFC 2765, February 2000.
 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
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 Resource Identifier (URI): Generic Syntax", STD 66,
 RFC 3986, January 2005.
 [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
 Architecture", RFC 4291, February 2006.
11.2. 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-04 (work in progress),
 January 2010.
 [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.
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
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 Masanobu Kawashima
 NEC AccessTechnica, Ltd.
 800, Shimomata
 Kakegawa-shi, Shizuoka 436-8501
 JAPAN
 Phone: +81 537 23 9655
 Email: kawashimam@necat.nec.co.jp
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