Internet Engineering Task Force S. Kawamura
Internet-Draft NEC BIGLOBE, Ltd.
Intended status: Informational M. Kawashima
Expires: October 23, 2009 NEC AccessTechnica, Ltd.
April 21, 2009
A Recommendation for IPv6 Address Text Representation
draft-kawamura-ipv6-text-representation-01
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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.
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While the IPv6 address architecture [RFC4291] 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 customers. The following draft will describe the
problems that a flexible text representation has been causing. This
document also recommends a canonical representation format that best
avoids confusion.
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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 . . . . . . . . . . . . . . . . . . . . . . 4
2.2. zero compression . . . . . . . . . . . . . . . . . . . . . 5
2.3. Uppercase or Lowercase . . . . . . . . . . . . . . . . . . 6
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 . . . . . . . . . . . . . . . . . 7
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 . . . . . . . . . . . . . . . . . . . 8
3.2.4. Auditing. Case 2 . . . . . . . . . . . . . . . . . . . 8
3.2.5. Unexpected Modifying . . . . . . . . . . . . . . . . . 8
3.3. Operating . . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. General Summary . . . . . . . . . . . . . . . . . . . 8
3.3.2. Customer Calls . . . . . . . . . . . . . . . . . . . . 9
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 . . . . . . . . 10
4.1. Handling Leading Zeros . . . . . . . . . . . . . . . . . . 10
4.2. "::" usage . . . . . . . . . . . . . . . . . . . . . . . . 10
4.2.1. shorten as much as possible . . . . . . . . . . . . . 10
4.2.2. one 16bit 0 field . . . . . . . . . . . . . . . . . . 10
4.2.3. when "::" can be used twice . . . . . . . . . . . . . 10
4.3. Lower Case . . . . . . . . . . . . . . . . . . . . . . . . 10
5. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . . 11
Appendix A. IPv6 Addresses with Embedded IPv4 Addresses . . . . . 12
Appendix B. For developers . . . . . . . . . . . . . . . . . . . 12
Appendix C. Prefix Issues . . . . . . . . . . . . . . . . . . . . 12
Appendix D. Phonetic Alphabet and Figure Code . . . . . . . . . . 12
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 flexiblity 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 RFC 2119 [RFC2119].
2. Text representation flexibility of RFC4291
Examples of flexibility in Section 2.2 of RFC4291 are described
below.
2.1. leading zeros
'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 16bit field is different, but all these addresses
are 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 16bits 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
... and more
In addition, RFC4291 in section 2.2 notes,
'The "::" can also be used to compress leading or trailing zeros
in an address.'
It is possible to choose whether to compress a leading zero or a
trailing zero in a single address. Examples are shown below.
2001:db8::aaaa:0:0:1
2001:db8:0:0:aaaa::1
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2.3. Uppercase or Lowercase
RFC4291 does not mention about preference of uppercase or lowercase.
Various flavors are shown below.
2001:db8:aaaa:bbbb:cccc:dddd:eeee:aaaa
2001:db8:aaaa:bbbb:cccc:dddd:eeee:AAAA
2001:db8:aaaa:bbbb:cccc:dddd:eeee:AaAa
... more combinations
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 reagular 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.
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3.1.3. Searching with Whois
The whois utility is used by a wide range of people today. When a
record is set to the whois database, one will likely check the output
to see if the entry is correct. If a entity was recorded as 2001:
db8::/48, but the whois ouput 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 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 of systems. 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. It must be noted that each additional line of a
program will result in increased development fees that will be
charged to the customers.
3.2.2. Logging
If an application were to ouput 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
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for human reading. This will result in additional code on the
applications which will result in extra fees charged to the
customers. 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
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 diffs that do
not take into account address representation rules.
3.2.4. Auditing. Case 2
Node configurations will be matched against a 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. An SNMP
GET of an interface address and text representation in a humanly
written text file is highly unlikely to match on first try.
3.2.5. 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 (which is seen in some
RIR databases). If the zeros were inputed 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. A distinguished engineer will know that
the right address is set, but an operator, or a customer that is
communicating with the operator to solve a problem, is usually not as
distinguished as we would like. Again, the extra load in checking
that the IP address is the same as was intended, will result in fees
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that will be charged to the customers.
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 NOC 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, but flexibility in address representation will increase the
work load which will again, result in fees that will be charged to
the customers, and also longer down time of systems.
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.
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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 RFC 4291, is implemented by
various operating systems, and is human friendly.
4.1. Handling Leading Zeros
Leading zeros should be chopped for human legibility and easier
searching. Also, a single 16 bit 0000 field should be represented as
just 0. Place holder zeros are often cause of mis-reading.
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 very clean).
4.2.2. one 16bit 0 field
"::" should not be used to shorten just one 16bit 0 field for it
would tend to mislead that there are more than one 16 bit field that
is shortened.
4.2.3. when "::" can be used twice
When cases where it is possible to use "::" in two or more different
sections of an address, implementation to shorten the side with more
16bit 0 fields are more common (i.e. latter is shortened in 2001:0:0:
1:0:0:0:1). When the length of 16bit 0 fields are equal (i.e. 2001:
db8:0:0:1:0:0:1), the former is usually shortened. One idea to avoid
any confusion, is for the operator to not use 16bit field 0 in the
first 64 bits. By nature IPv6 addresses are usually assigned or
allocated to end-users as longer than 32 bits (typicaly 48bit 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. Conclusion
The recommended format of text representing an IPv6 address is
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summarized as follows.
(1) omit leading zeros
(2) "::" used to their maximum extent whenever possible
(3) "::" used where shortens address the most
(4) "::" used in the former part in case of a tie breaker
(5) do not shorten one 16bit 0 field
(6) use lower case
Hints for developers are written in the Appendix section.
6. Security Considerations
None.
7. IANA Considerations
None.
8. Acknowledgements
The authors would like to thank Jan Zorz, Randy Bush, Yuichi Minami,
Toshimitsu Matsuura for their generous and helpful comments.
9. References
9.1. Normative References
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, February 2006.
9.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
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[RFC4038] Shin, M-K., Hong, Y-G., Hagino, J., Savola, P., and E.
Castro, "Application Aspects of IPv6 Transition",
RFC 4038, March 2005.
[RFC5156] Blanchet, M., "Special-Use IPv6 Addresses", RFC 5156,
April 2008.
Appendix A. IPv6 Addresses with Embedded IPv4 Addresses
IPv4-Compatible IPv6 address and IPv4-Mapped IPv6 address are defined
that carry an IPv4 address in the low-order 32 bits of the address.
These addresses have special representation that combine hexadecimal
and decimal notations. IPv4-Compatible IPv6 address is deprecated.
Although the use of IPv4-Mapped IPv6 address is not recommended due
to security and portability problems, the text representation method
noted in this document should be applied for the hexadecimal part.
Appendix B. 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.
The function inet_ntop() of FreeBSD7.0 is a good C code reference,
but should not be called directly. See RFC4038 for details.
Appendix C. Prefix Issues
Problems with prefixes are just the same as problems encountered with
addresses. Text representation method of IPv6 prefixes should be no
different from that of IPv6 addresses.
Appendix D. Phonetic Alphabet and Figure Code
The use of Phonetics Alphabet is essential for complete accuracy in
voice communications. For example, ITU Phonetic alphabet and Figure
Code is as follows (extracted hexadecimal from it):
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+-----------+------------+----------------------+
| Character | Word | Pronunciation |
+-----------+------------+----------------------+
| 0 | Nadazero | NAH-DAH-ZAY-ROH |
| 1 | Unaone | OO-NAH-WUN |
| 2 | Bissotwo | BEES-SOH-TOO |
| 3 | Terrathree | TAY-RAH-TREE |
| 4 | Kartefour | KAR-TAY-FOWER |
| 5 | Pantafive | PAN-TAH-FIVE |
| 6 | Soxisix | SOK-SEE-SIX |
| 7 | Setteseven | SAY-TAY-SEVEN |
| 8 | Oktoeight | OK-TOH-AIT |
| 9 | Novenine | NO-VAY-NINER |
| A | Alfa | AL FAH |
| B | Bravo | BRAH VOH |
| C | Charlie | CHAR LEE or SHAR LEE |
| D | Delta | DELL TAH |
| E | Echo | ECK OH |
| F | Foxtrot | FOKS TROT |
+-----------+------------+----------------------+
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
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