draft-ietf-6man-text-addr-representation-07.txt   rfc5952.txt 
IPv6 Maintenance Working Group S. Kawamura Internet Engineering Task Force (IETF) S. Kawamura
Internet-Draft NEC BIGLOBE, Ltd. Request for Comments: 5952 NEC BIGLOBE, Ltd.
Updates: 4291 (if approved) M. Kawashima Updates: 4291 M. Kawashima
Intended status: Standards Track NEC AccessTechnica, Ltd. Category: Standards Track NEC AccessTechnica, Ltd.
Expires: August 29, 2010 February 25, 2010 ISSN: 2070-1721 August 2010
A Recommendation for IPv6 Address Text Representation A Recommendation for IPv6 Address Text Representation
draft-ietf-6man-text-addr-representation-07
Abstract Abstract
As IPv6 deployment increases there will be a dramatic increase in the As IPv6 deployment increases, there will be a dramatic increase in
need to use IPv6 addresses in text. While the IPv6 address the need to use IPv6 addresses in text. While the IPv6 address
architecture in RFC 4291 section 2.2 describes a flexible model for architecture in Section 2.2 of RFC 4291 describes a flexible model
text representation of an IPv6 address this flexibility has been for text representation of an IPv6 address, this flexibility has been
causing problems for operators, system engineers, and users. This causing problems for operators, system engineers, and users. This
document defines a canonical textual representation format. It does document defines a canonical textual representation format. It does
not define a format for internal storage, such as within an not define a format for internal storage, such as within an
application or database. It is expected that the canonical format is application or database. It is expected that the canonical format
followed by humans and systems when representing IPv6 addresses as will be followed by humans and systems when representing IPv6
text, but all implementations must accept and be able to handle any addresses as text, but all implementations must accept and be able to
legitimate RFC 4291 format. 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 Status of This Memo
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at This is an Internet Standards Track document.
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at This document is a product of the Internet Engineering Task Force
http://www.ietf.org/shadow.html. (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on August 29, 2010. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc5952.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
skipping to change at page 2, line 15 skipping to change at page 2, line 18
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Text Representation Flexibility of RFC4291 . . . . . . . . . . 4 2. Text Representation Flexibility of RFC 4291 . . . . . . . . . 4
2.1. Leading Zeros in a 16 Bit Field . . . . . . . . . . . . . 4 2.1. Leading Zeros in a 16-Bit Field . . . . . . . . . . . . . 4
2.2. Zero Compression . . . . . . . . . . . . . . . . . . . . . 5 2.2. Zero Compression . . . . . . . . . . . . . . . . . . . . . 5
2.3. Uppercase or Lowercase . . . . . . . . . . . . . . . . . . 5 2.3. Uppercase or Lowercase . . . . . . . . . . . . . . . . . . 6
3. Problems Encountered with the Flexible Model . . . . . . . . . 6 3. Problems Encountered with the Flexible Model . . . . . . . . . 6
3.1. Searching . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. Searching . . . . . . . . . . . . . . . . . . . . . . . . 6
3.1.1. General Summary . . . . . . . . . . . . . . . . . . . 6 3.1.1. General Summary . . . . . . . . . . . . . . . . . . . 6
3.1.2. Searching Spreadsheets and Text Files . . . . . . . . 6 3.1.2. Searching Spreadsheets and Text Files . . . . . . . . 6
3.1.3. Searching with Whois . . . . . . . . . . . . . . . . . 6 3.1.3. Searching with Whois . . . . . . . . . . . . . . . . . 6
3.1.4. Searching for an Address in a Network Diagram . . . . 7 3.1.4. Searching for an Address in a Network Diagram . . . . 7
3.2. Parsing and Modifying . . . . . . . . . . . . . . . . . . 7 3.2. Parsing and Modifying . . . . . . . . . . . . . . . . . . 7
3.2.1. General Summary . . . . . . . . . . . . . . . . . . . 7 3.2.1. General Summary . . . . . . . . . . . . . . . . . . . 7
3.2.2. Logging . . . . . . . . . . . . . . . . . . . . . . . 7 3.2.2. Logging . . . . . . . . . . . . . . . . . . . . . . . 7
3.2.3. Auditing: Case 1 . . . . . . . . . . . . . . . . . . . 7 3.2.3. Auditing: Case 1 . . . . . . . . . . . . . . . . . . . 8
3.2.4. Auditing: Case 2 . . . . . . . . . . . . . . . . . . . 8 3.2.4. Auditing: Case 2 . . . . . . . . . . . . . . . . . . . 8
3.2.5. Verification . . . . . . . . . . . . . . . . . . . . . 8 3.2.5. Verification . . . . . . . . . . . . . . . . . . . . . 8
3.2.6. Unexpected Modifying . . . . . . . . . . . . . . . . . 8 3.2.6. Unexpected Modifying . . . . . . . . . . . . . . . . . 8
3.3. Operating . . . . . . . . . . . . . . . . . . . . . . . . 8 3.3. Operating . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. General Summary . . . . . . . . . . . . . . . . . . . 8 3.3.1. General Summary . . . . . . . . . . . . . . . . . . . 8
3.3.2. Customer Calls . . . . . . . . . . . . . . . . . . . . 8 3.3.2. Customer Calls . . . . . . . . . . . . . . . . . . . . 9
3.3.3. Abuse . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3.3. Abuse . . . . . . . . . . . . . . . . . . . . . . . . 9
3.4. Other Minor Problems . . . . . . . . . . . . . . . . . . . 9 3.4. Other Minor Problems . . . . . . . . . . . . . . . . . . . 9
3.4.1. Changing Platforms . . . . . . . . . . . . . . . . . . 9 3.4.1. Changing Platforms . . . . . . . . . . . . . . . . . . 9
3.4.2. Preference in Documentation . . . . . . . . . . . . . 9 3.4.2. Preference in Documentation . . . . . . . . . . . . . 9
3.4.3. Legibility . . . . . . . . . . . . . . . . . . . . . . 9 3.4.3. Legibility . . . . . . . . . . . . . . . . . . . . . . 9
4. A Recommendation for IPv6 Text Representation . . . . . . . . 9 4. A Recommendation for IPv6 Text Representation . . . . . . . . 10
4.1. Handling Leading Zeros in a 16 Bit Field . . . . . . . . . 10 4.1. Handling Leading Zeros in a 16-Bit Field . . . . . . . . . 10
4.2. "::" Usage . . . . . . . . . . . . . . . . . . . . . . . . 10 4.2. "::" Usage . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2.1. Shorten As Much As Possible . . . . . . . . . . . . . 10 4.2.1. Shorten as Much as Possible . . . . . . . . . . . . . 10
4.2.2. Handling One 16 Bit 0 Field . . . . . . . . . . . . . 10 4.2.2. Handling One 16-Bit 0 Field . . . . . . . . . . . . . 10
4.2.3. Choice in Placement of "::" . . . . . . . . . . . . . 10 4.2.3. Choice in Placement of "::" . . . . . . . . . . . . . 10
4.3. Lower Case . . . . . . . . . . . . . . . . . . . . . . . . 10 4.3. Lowercase . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Text Representation of Special Addresses . . . . . . . . . . . 10 5. Text Representation of Special Addresses . . . . . . . . . . . 11
6. Notes on Combining IPv6 Addresses with Port Numbers . . . . . 11 6. Notes on Combining IPv6 Addresses with Port Numbers . . . . . 11
7. Prefix Representation . . . . . . . . . . . . . . . . . . . . 12 7. Prefix Representation . . . . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations . . . . . . . . . . . . . . . . . . . 12
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 10.1. Normative References . . . . . . . . . . . . . . . . . . . 12
11.1. Normative References . . . . . . . . . . . . . . . . . . . 12 10.2. Informative References . . . . . . . . . . . . . . . . . . 13
11.2. Informative References . . . . . . . . . . . . . . . . . . 13 Appendix A. For Developers . . . . . . . . . . . . . . . . . . . 14
Appendix A. For Developers . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
A single IPv6 address can be text represented in many ways. Examples A single IPv6 address can be text represented in many ways. Examples
are shown below. are shown below.
2001:db8:0:0:1:0:0:1 2001:db8:0:0:1:0:0:1
2001:0db8:0:0:1:0:0:1 2001:0db8:0:0:1:0:0:1
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2001:0db8::1:0:0:1 2001:0db8::1:0:0:1
2001:db8:0:0:1::1 2001:db8:0:0:1::1
2001:db8:0000:0:1::1 2001:db8:0000:0:1::1
2001:DB8:0:0:1::1 2001:DB8:0:0:1::1
All of the above examples represent the same IPv6 address. This All of the above examples represent the same IPv6 address. This
flexibility has caused many problems for operators, systems flexibility has caused many problems for operators, systems
engineers, and customers. The problems are noted in Section 3. engineers, and customers. The problems are noted in Section 3. A
Also, a canonical representation format to avoid problems is canonical representation format to avoid problems is introduced in
introduced in Section 4. Section 4.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
2. Text Representation Flexibility of RFC4291 2. Text Representation Flexibility of RFC 4291
Examples of flexibility in Section 2.2 of [RFC4291] are described Examples of flexibility in Section 2.2 of [RFC4291] are described
below. below.
2.1. Leading Zeros in a 16 Bit Field 2.1. Leading Zeros in a 16-Bit Field
'It is not necessary to write the leading zeros in an individual 'It is not necessary to write the leading zeros in an individual
field.' field.'
Conversely it is also not necessary to omit leading zeros. This Conversely, it is also not necessary to omit leading zeros. This
means that, it is possible to select from such as the following means that it is possible to select from representations such as
example. The final 16 bit field is different, but all these those in the following example. The final 16-bit field is different,
addresses represent the same address. but all of these addresses represent the same address.
2001:db8:aaaa:bbbb:cccc:dddd:eeee:0001 2001:db8:aaaa:bbbb:cccc:dddd:eeee:0001
2001:db8:aaaa:bbbb:cccc:dddd:eeee:001 2001:db8:aaaa:bbbb:cccc:dddd:eeee:001
2001:db8:aaaa:bbbb:cccc:dddd:eeee:01 2001:db8:aaaa:bbbb:cccc:dddd:eeee:01
2001:db8:aaaa:bbbb:cccc:dddd:eeee:1 2001:db8:aaaa:bbbb:cccc:dddd:eeee:1
2.2. Zero Compression 2.2. Zero Compression
'A special syntax is available to compress the zeros. The use of 'A special syntax is available to compress the zeros. The use of
"::" indicates one or more groups of 16 bits of zeros.' "::" 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 It is possible to select whether or not to omit just one 16-bit 0
zeros. field.
2001:db8:aaaa:bbbb:cccc:dddd::1 2001:db8:aaaa:bbbb:cccc:dddd::1
2001:db8:aaaa:bbbb:cccc:dddd:0:1 2001:db8:aaaa:bbbb:cccc:dddd:0:1
In case where there is more than one zero fields, there is a choice In cases where there is more than one field of only zeros, there is a
of how many fields can be shortened. choice of how many fields can be shortened.
2001:db8:0:0:0::1 2001:db8:0:0:0::1
2001:db8:0:0::1 2001:db8:0:0::1
2001:db8:0::1 2001:db8:0::1
2001:db8::1 2001:db8::1
In addition, [RFC4291] in section 2.2 notes, In addition, Section 2.2 of [RFC4291] notes,
'The "::" can only appear once in an address.' 'The "::" can only appear once in an address.'
This gives a choice on where in a single address to compress the This gives a choice on where in a single address to compress the
zero. zero.
2001:db8::aaaa:0:0:1 2001:db8::aaaa:0:0:1
2001:db8:0:0:aaaa::1 2001:db8:0:0:aaaa::1
skipping to change at page 6, line 18 skipping to change at page 6, line 22
2001:db8:aaaa:bbbb:cccc:dddd:eeee:AaAa 2001:db8:aaaa:bbbb:cccc:dddd:eeee:AaAa
3. Problems Encountered with the Flexible Model 3. Problems Encountered with the Flexible Model
3.1. Searching 3.1. Searching
3.1.1. General Summary 3.1.1. General Summary
A search of an IPv6 address if conducted through a UNIX system is A search of an IPv6 address if conducted through a UNIX system is
usually case sensitive and extended options to allow for regular usually case sensitive and extended options that allow for regular
expression use will come in handy. However, there are many expression use will come in handy. However, there are many
applications in the Internet today that do not provide this applications in the Internet today that do not provide this
capability. When searching for an IPv6 address in such systems, the capability. When searching for an IPv6 address in such systems, the
system engineer will have to try each and every possibility to search system engineer will have to try each and every possibility to search
for an address. This has critical impacts especially when trying to for an address. This has critical impacts, especially when trying to
deploy IPv6 over an enterprise network. deploy IPv6 over an enterprise network.
3.1.2. Searching Spreadsheets and Text Files 3.1.2. Searching Spreadsheets and Text Files
Spreadsheet applications and text editors on GUI systems, rarely have Spreadsheet applications and text editors on GUI systems rarely have
the ability to search for a text using regular expression. Moreover, the ability to search for text using regular expression. Moreover,
there are many non-engineers (who are not aware of case sensitivity there are many non-engineers (who are not aware of case sensitivity
and regular expression use) that use these application to manage IP and regular expression use) that use these applications to manage IP
addresses. This has worked quite well with IPv4 since text addresses. This has worked quite well with IPv4 since text
representation in IPv4 has very little flexibility. There is no representation in IPv4 has very little flexibility. There is no
incentive to encourage these non-engineers to change their tool or incentive to encourage these non-engineers to change their tool or
learn regular expression when they decide to go dual-stack. If the 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 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. 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 One example where this will cause a problem is, when the search is
being conducted to assign a new address from a pool, and a check was being conducted to assign a new address from a pool, and a check is
being done to see if it was not in use. This may cause problems to being done to see if it is not in use. This may cause problems for
the end-hosts or end-users. This type of address management is very the end-hosts or end-users. This type of address management is very
often seen in enterprise networks and also in ISPs. often seen in enterprise networks and ISPs.
3.1.3. Searching with Whois 3.1.3. Searching with Whois
The "whois" utility is used by a wide range of people today. When a 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 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, 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 but the whois output showed 2001:0db8:0000::/48, most non-engineers
would think that their input was wrong and will likely retry several would think that their input was wrong and will likely retry several
times or make a frustrated call to the database hostmaster. If there times or make a frustrated call to the database hostmaster. If there
was a need to register the same address on different systems, and was a need to register the same prefix on different systems, and each
each system showed a different text representation, this would system showed a different text representation, this would confuse
confuse people even more. Although this document focuses on people even more. Although this document focuses on addresses rather
addresses rather than prefixes, this is worth mentioning since the than prefixes, it is worth mentioning the prefix problems because the
problems encountered are mostly equal. problems encountered with addresses and prefixes are mostly equal.
3.1.4. Searching for an Address in a Network Diagram 3.1.4. Searching for an Address in a Network Diagram
Network diagrams and blueprints often show what IP addresses are Network diagrams and blueprints often show what IP addresses are
assigned to a system devices. In times of trouble shooting there may 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 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 (for example, if a traceroute stopped at 2001:db8::1, one would
search the diagram for that address). This is a technique quite search the diagram for that address). This is a technique quite
often in use in enterprise networks and managed services. Again, the often in use in enterprise networks and managed services. Again, the
different flavors of text representation will result in a time- different flavors of text representation will result in a time-
consuming search leading to longer MTTR in times of trouble. consuming search leading to longer mean times to restoration (MTTR)
in times of trouble.
3.2. Parsing and Modifying 3.2. Parsing and Modifying
3.2.1. General Summary 3.2.1. General Summary
With all the possible methods of text representation each application With all the possible methods of text representation, each
must include a module, object, link, etc. to a function that will application must include a module, object, link, etc. to a function
parse IPv6 addresses in a manner that no matter how it is that will parse IPv6 addresses in a manner such that no matter how it
represented, they will mean the same address. Many system engineers is represented, they will mean the same address. Many system
who integrate complex computer systems for corporate customers will engineers who integrate complex computer systems for corporate
have difficulties finding that their favorite tool will not have this customers will have difficulties finding that their favorite tool
function, or will encounter difficulties such as having to rewrite will not have this function, or will encounter difficulties such as
their macros or scripts for their customers. having to rewrite their macros or scripts for their customers.
3.2.2. Logging 3.2.2. Logging
If an application were to output a log summary that represented the 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), 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 output would be highly unreadable compared to the IPv4 output.
The address would have to be parsed and reformed to make it useful The address would have to be parsed and reformed to make it useful
for human reading. Sometimes logging for critical systems is done by for human reading. Sometimes logging for critical systems is done by
mirroring the same traffic to two different systems. Care must be 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 taken so that no matter what the log output is, the logs should be
parsed so they will mean the same. parsed so they are equivalent.
3.2.3. Auditing: Case 1 3.2.3. Auditing: Case 1
When a router or any other network appliance machine configuration is When a router or any other network appliance machine configuration is
audited, there are many methods to compare the configuration audited, there are many methods to compare the configuration
information of a node. Sometimes auditing will be done by just information of a node. Sometimes auditing will be done by just
comparing the changes made each day. In this case if configuration 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: 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 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 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 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 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 real auditing. Lots of tools are just plain diffs that do not take
into account address representation rules. into account address representation rules.
3.2.4. Auditing: Case 2 3.2.4. Auditing: Case 2
Node configurations will be matched against an information system Node configurations will be matched against an information system
that manages IP addresses. If output notation is different there that manages IP addresses. If output notation is different, there
will need to be a script that is implemented to cover for this. The 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 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 textual address written by a human is highly unlikely to match on the
first try. first try.
3.2.5. Verification 3.2.5. Verification
Some protocols require certain data fields to be verified. One Some protocols require certain data fields to be verified. One
example of this is X.509 certificates. If an IPv6 address field in a example of this is X.509 certificates. If an IPv6 address field in a
certificate was incorrectly verified by converting it to text and certificate was incorrectly verified by converting it to text and
skipping to change at page 8, line 51 skipping to change at page 9, line 9
When an operator sets an IPv6 address of a system as 2001:db8:0:0:1: 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 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 result as 2001:DB8::1:0:0:1. Someone familiar with IPv6 address
representation will know that the right address is set, but not representation will know that the right address is set, but not
everyone may understand this. everyone may understand this.
3.3.2. Customer Calls 3.3.2. Customer Calls
When a customer calls to inquire about a suspected outage, IPv6 When a customer calls to inquire about a suspected outage, IPv6
address representation should be handled with care. Not all address representation should be handled with care. Not all
customers are engineers nor have the same skill in IPv6 technology. customers are engineers, nor do they have a similar skill level in
The network operations center will have to take extra steps to IPv6 technology. The network operations center will have to take
humanly parse the address to avoid having to explain to the customers extra steps to humanly parse the address to avoid having to explain
that 2001:db8:0:1::1 is the same as 2001:db8::1:0:0:0:1. This is one to the customers that 2001:db8:0:1::1 is the same as
thing that will never happen in IPv4 because IPv4 address cannot be 2001:db8::1:0:0:0:1. This is one thing that will never happen in
abbreviated. IPv4 because IPv4 addresses cannot be abbreviated.
3.3.3. Abuse 3.3.3. Abuse
Network abuse reports generally include the abusing IP address. This Network abuse reports generally include the abusing IP address. This
'reporting' could take any shape or form of the flexible model. A 'reporting' could take any shape or form of the flexible model. A
team that handles network abuse must be able to tell the difference 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 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 placement of the "::" will result in a critical situation. A system
that handles these incidents should be able to handle any type of that handles these incidents should be able to handle any type of
input and parse it in a correct manner. Also, incidents are reported 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 over the phone. It is unnecessary to report if the letter is
uppercase or lowercase. However, when a letter is spelled uppercase, uppercase or lowercase. However, when a letter is spelled uppercase,
people tend to clarify that it is uppercase, which is unnecessary people tend to specify that it is uppercase, which is unnecessary
information. information.
3.4. Other Minor Problems 3.4. Other Minor Problems
3.4.1. Changing Platforms 3.4.1. Changing Platforms
When an engineer decides to change the platform of a running service, 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 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. address text representation. Usually, a change in a platform (e.g.,
Unix to Windows, Cisco to Juniper) will result in a major change of Unix to Windows, Cisco to Juniper) will result in a major change of
code anyway, but flexibility in address representation will increase code anyway, but flexibility in address representation will increase
the work load. the work load.
3.4.2. Preference in Documentation 3.4.2. Preference in Documentation
A document that is edited by more than one author may become harder A document that is edited by more than one author may become harder
to read. to read.
3.4.3. Legibility 3.4.3. Legibility
Capital case D and 0 can be quite often misread. Capital B and 8 can Capital case D and 0 can be quite often misread. Capital B and 8 can
also be misread. also be misread.
4. A Recommendation for IPv6 Text Representation 4. A Recommendation for IPv6 Text Representation
A recommendation for a canonical text representation format of IPv6 A recommendation for a canonical text representation format of IPv6
addresses is presented in this section. The recommendation in this addresses is presented in this section. The recommendation in this
document is one that, complies fully with [RFC4291], is implemented document is one that complies fully with [RFC4291], is implemented by
by various operating systems, and is human friendly. The various operating systems, and is human friendly. The recommendation
recommendation in this section SHOULD be followed by systems when in this section SHOULD be followed by systems when generating an
generating an address to represent as text, but all implementations address to be represented as text, but all implementations MUST
MUST accept and be able to handle any legitimate [RFC4291] format. accept and be able to handle any legitimate [RFC4291] format. It is
It is advised that humans also follow these recommendations when advised that humans also follow these recommendations when spelling
spelling an address. an address.
4.1. Handling Leading Zeros in a 16 Bit Field 4.1. Handling Leading Zeros in a 16-Bit Field
Leading zeros MUST be suppressed. For example 2001:0db8::0001 is not Leading zeros MUST be suppressed. For example, 2001:0db8::0001 is
acceptable and must be represented as 2001:db8::1. A single 16 bit not acceptable and must be represented as 2001:db8::1. A single 16-
0000 field MUST be represented as 0. bit 0000 field MUST be represented as 0.
4.2. "::" Usage 4.2. "::" Usage
4.2.1. Shorten As Much As Possible 4.2.1. Shorten as Much as Possible
The use of symbol "::" MUST be used to its maximum capability. For The use of the symbol "::" MUST be used to its maximum capability.
example, 2001:db8::0:1 is not acceptable, because the symbol "::" For example, 2001:db8:0:0:0:0:2:1 must be shortened to 2001:db8::2:1.
Likewise, 2001:db8::0:1 is not acceptable, because the symbol "::"
could have been used to produce a shorter representation 2001:db8::1. could have been used to produce a shorter representation 2001:db8::1.
4.2.2. Handling One 16 Bit 0 Field 4.2.2. Handling One 16-Bit 0 Field
The symbol "::" MUST NOT be used to shorten just 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 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. 2001:db8::1:1:1:1:1 is not correct.
4.2.3. Choice in Placement of "::" 4.2.3. Choice in Placement of "::"
When there is an alternative choice in the placement of a "::", the 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. longest run of consecutive 16-bit 0 fields MUST be shortened (i.e.,
the sequence with three consecutive zero fields is shortened in 2001: 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 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 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 bits MUST be shortened. For example, 2001:db8::1:0:0:1 is correct
representation. representation.
4.3. Lower Case 4.3. Lowercase
The characters "a", "b", "c", "d", "e", "f" in an IPv6 address MUST The characters "a", "b", "c", "d", "e", and "f" in an IPv6 address
be represented in lower case. MUST be represented in lowercase.
5. Text Representation of Special Addresses 5. Text Representation of Special Addresses
Addresses such as IPv4-Mapped IPv6 addresses, ISATAP [RFC5214], and Addresses such as IPv4-Mapped IPv6 addresses, ISATAP [RFC5214], and
IPv4-translatable addresses [I-D.ietf-behave-address-format] have IPv4-translatable addresses [ADDR-FORMAT] have IPv4 addresses
IPv4 addresses embedded in the low-order 32 bits of the address. embedded in the low-order 32 bits of the address. These addresses
These addresses have special representation that may mix hexadecimal have a special representation that may mix hexadecimal and dot
and dot decimal notations. The decimal notation may be used only for decimal notations. The decimal notation may be used only for the
the last 32 bits of the address. For these addresses, mixed notation last 32 bits of the address. For these addresses, mixed notation is
is RECOMMENDED if the following condition is met: The address can be RECOMMENDED if the following condition is met: the address can be
distinguished as having IPv4 addresses embedded in the lower 32 bits distinguished as having IPv4 addresses embedded in the lower 32 bits
solely from the address field through the use of a well known prefix. 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 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 this writing. If it is known by some external method that a given
is used to embed IPv4, it MAY be represented as mixed notation. prefix is used to embed IPv4, it MAY be represented as mixed
Tools that provide options to specify prefixes that are (or are not) notation. Tools that provide options to specify prefixes that are
to be represented as mixed notation may be useful. (or are not) to be represented as mixed notation may be useful.
There is a trade-off here where a recommendation to achieve exact There is a trade-off here where a recommendation to achieve an exact
match in a search (no dot decimals whatsoever) and recommendation to match in a search (no dot decimals whatsoever) and a recommendation
help the readability of an addresses (dot decimal whenever possible) to help the readability of an address (dot decimal whenever possible)
does not result in the same solution. The above recommendation is does not result in the same solution. The above recommendation is
aimed at fixing the representation as much as possible while leaving aimed at fixing the representation as much as possible while leaving
the opportunity for future well known prefixes to be represented in a the opportunity for future well-known prefixes to be represented in a
human friendly manner as tools adjust to newly assigned prefixes. human-friendly manner as tools adjust to newly assigned prefixes.
The text representation method noted in Section 4 should be applied 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 for the leading hexadecimal part (i.e., ::ffff:192.0.2.1 instead of
0:0:0:0:0:ffff:192.0.2.1). 0:0:0:0:0:ffff:192.0.2.1).
6. Notes on Combining IPv6 Addresses with Port Numbers 6. Notes on Combining IPv6 Addresses with Port Numbers
When IPv6 addresses and port numbers are represented in text combined There are many different ways to combine IPv6 addresses and port
together, there are many different ways to do so. Examples are shown numbers that are represented in text. Examples are shown below.
below.
o [2001:db8::1]:80 o [2001:db8::1]:80
o 2001:db8::1:80 o 2001:db8::1:80
o 2001:db8::1.80 o 2001:db8::1.80
o 2001:db8::1 port 80 o 2001:db8::1 port 80
o 2001:db8::1p80 o 2001:db8::1p80
o 2001:db8::1#80 o 2001:db8::1#80
The situation is not much different in IPv4, but the most ambiguous 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 case with IPv6 is the second bullet. This is due to the "::"usage in
IPv6 addresses. This style is NOT RECOMMENDED for its ambiguity. IPv6 addresses. This style is NOT RECOMMENDED because of its
The [] style as expressed in [RFC3986] SHOULD be employed, and is the ambiguity. The [] style as expressed in [RFC3986] SHOULD be
default unless otherwise specified. Other styles are acceptable when employed, and is the default unless otherwise specified. Other
there is exactly one style for the given context and cross-platform styles are acceptable when there is exactly one style for the given
portability does not become an issue. For URIs containing IPv6 context and cross-platform portability does not become an issue. For
address literals, [RFC3986] MUST be followed, as well as the rules in URIs containing IPv6 address literals, [RFC3986] MUST be followed, as
this document. well as the rules defined in this document.
7. Prefix Representation 7. Prefix Representation
Problems with prefixes are just the same as problems encountered with Problems with prefixes are the same as problems encountered with
addresses. The text representation method of IPv6 prefixes should be addresses. The text representation method of IPv6 prefixes should be
no different from that of IPv6 addresses. no different from that of IPv6 addresses.
8. Security Considerations 8. Security Considerations
This document notes some examples where IPv6 addresses are compared 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 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 security risk if used for access control. The common practice of
comparing X.509 data is done in binary format. comparing X.509 data is done in binary format.
9. IANA Considerations 9. Acknowledgements
None.
10. Acknowledgements
The authors would like to thank Jan Zorz, Randy Bush, Yuichi Minami, The authors would like to thank Jan Zorz, Randy Bush, Yuichi Minami,
Toshimitsu Matsuura for their generous and helpful comments in kick and Toshimitsu Matsuura for their generous and helpful comments in
starting this document. We also would like to thank Brian Carpenter, kick starting this document. We also would like to thank Brian
Akira Kato, Juergen Schoenwaelder, Antonio Querubin, Dave Thaler, Carpenter, Akira Kato, Juergen Schoenwaelder, Antonio Querubin, Dave
Brian Haley, Suresh Krishnan, Jerry Huang, Roman Donchenko, Heikki Thaler, Brian Haley, Suresh Krishnan, Jerry Huang, Roman Donchenko,
Vatiainen ,Dan Wing, and Doug Barton for their input. Also a very Heikki Vatiainen, Dan Wing, and Doug Barton for their input. Also, a
special thanks to Ron Bonica, Fred Baker, Brian Haberman, Robert very special thanks to Ron Bonica, Fred Baker, Brian Haberman, Robert
Hinden, Jari Arkko, and Kurt Lindqvist for their support in bringing Hinden, Jari Arkko, and Kurt Lindqvist for their support in bringing
this document to the light of IETF working groups. this document to light in IETF working groups.
11. References 10. References
11.1. Normative References 10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm [RFC2765] Nordmark, E., "Stateless IP/ICMP Translation Algorithm
(SIIT)", RFC 2765, February 2000. (SIIT)", RFC 2765, February 2000.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter,
Resource Identifier (URI): Generic Syntax", STD 66, "Uniform Resource Identifier (URI): Generic Syntax",
RFC 3986, January 2005. STD 66, RFC 3986, January 2005.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing [RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006. Architecture", RFC 4291, February 2006.
11.2. Informative References 10.2. Informative References
[I-D.ietf-behave-address-format] [ADDR-FORMAT] Bao, C., "IPv6 Addressing of IPv4/IPv6 Translators",
Huitema, C., Bao, C., Bagnulo, M., Boucadair, M., and X. Work in Progress, July 2010.
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. [RFC4038] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
Castro, "Application Aspects of IPv6 Transition", Castro, "Application Aspects of IPv6 Transition",
RFC 4038, March 2005. RFC 4038, March 2005.
[RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site [RFC5214] Templin, F., Gleeson, T., and D. Thaler, "Intra-Site
Automatic Tunnel Addressing Protocol (ISATAP)", RFC 5214, Automatic Tunnel Addressing Protocol (ISATAP)",
March 2008. RFC 5214, March 2008.
Appendix A. For Developers Appendix A. For Developers
We recommend that developers use display routines that conform to We recommend that developers use display routines that conform to
these rules. For example, the usage of getnameinfo() with flags these rules. For example, the usage of getnameinfo() with flags
argument NI_NUMERICHOST in FreeBSD 7.0 will give a conforming output, argument NI_NUMERICHOST in FreeBSD 7.0 will give a conforming output,
except for the special addresses notes in Section 5. The function 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 inet_ntop() of FreeBSD7.0 is a good C code reference, but should not
be called directly. See [RFC4038] for details. be called directly. See [RFC4038] for details.
Authors' Addresses Authors' Addresses
Seiichi Kawamura Seiichi Kawamura
NEC BIGLOBE, Ltd. NEC BIGLOBE, Ltd.
14-22, Shibaura 4-chome 14-22, Shibaura 4-chome
Minatoku, Tokyo 108-8558 Minatoku, Tokyo 108-8558
JAPAN JAPAN
Phone: +81 3 3798 6085 Phone: +81 3 3798 6085
Email: kawamucho@mesh.ad.jp EMail: kawamucho@mesh.ad.jp
Masanobu Kawashima Masanobu Kawashima
NEC AccessTechnica, Ltd. NEC AccessTechnica, Ltd.
800, Shimomata 800, Shimomata
Kakegawa-shi, Shizuoka 436-8501 Kakegawa-shi, Shizuoka 436-8501
JAPAN JAPAN
Phone: +81 537 23 9655 Phone: +81 537 23 9655
Email: kawashimam@necat.nec.co.jp EMail: kawashimam@necat.nec.co.jp
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