Behave WG T. Savolainen
Internet-Draft Nokia
Intended status: Informational J. Korhonen
Expires: August 19, 2011 Nokia Siemens Networks
February 15, 2011
Discovery of a Network-Specific NAT64 Prefix using a Well-Known Name
draft-savolainen-heuristic-nat64-discovery-01.txt
Abstract
This document describes a method for detecting presence of DNS64 and
for learning IPv6 prefix used for protocol translation on an access
network without explicit support from the access network. The method
depends on existence of a known IPv4-only domain name. The
information learned enables applications and hosts to perform local
IPv6 address synthesis and on dual-stack accesses avoid traversal
through NAT64.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 19, 2011.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3
2.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Host behavior . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Connectivity test . . . . . . . . . . . . . . . . . . . . . 5
3.2. IPv4 addresses of the known name . . . . . . . . . . . . . 5
3.3. Non-standard IPv6 address formats . . . . . . . . . . . . . 6
4. Hosting of an IPv4-only name(s) . . . . . . . . . . . . . . . . 6
5. Required IPv4 addresses . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
9. Normative References . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
As part of the transition to IPv6 NAT64
[I-D.ietf-behave-v6v4-xlate-stateful] and DNS64
[I-D.ietf-behave-dns64] technologies will be utilized by some access
networks to provide IPv4 connectivity for IPv6-only hosts. The DNS64
utilizes IPv6 address synthesis to create local IPv6 presentations of
peers having only IPv4 addresses, hence allowing DNS-using IPv6-only
hosts to communicate with IPv4-only peers.
However, DNS64 cannot serve applications not using DNS, such as those
receiving IPv4 address literals as referrals. Such applications
could nevertheless be able to work through NAT64, provided they are
able to create locally valid IPv6 presentations of peers' IPv4
addresses.
Additionally, DNS64 is not able to do IPv6 address synthesis for
hosts running validating DNSSEC enabled resolvers, but instead the
synthetization must be done by the hosts. In order to perform IPv6
synthesis hosts have to learn the IPv6 prefix(es) used on the access
network for protocol translation.
This document describes a best effort method for advanced
applications and hosts to learn the information required to perform
local IPv6 address synthesis. An example application is a browser
encountering an IPv4 address literal in an IPv6-only access network.
Another example is a host running validating security aware DNS
resolver.
The knowledge of IPv6 address synthetization taking place may also be
useful if DNS64 and NAT64 are present in dual-stack enabled access
network. In such cases hosts may choose to prefer IPv4 in order to
avoid traversal through protocol translators.
The described method is intented for the scenarios where network
assisted NAT64 and prefix discovery solutions are not available.
2. Requirements and Terminology
2.1. Requirements
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].
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2.2. Terminology
Known Name: a fully qualified domain name known by the implementation
to have only an A record. Implementation knows it by hard-coding or
e.g. via some provisioning technology. The name is not known by
everybody.
Well-Known IPv4-only Name: a fully qualified domain name well-known
to have only A record.
3. Host behavior
A host requiring information about presence of NAT64 and the IPv6
prefix used for protocol translation shall send a DNS query for AAAA
records of a known IPv4-only fully qualified domain name. This may
happen, for example, at the moment the host is configured an IPv6
address of a DNS server. This may also happen at the time when first
DNS query for AAAA record is initiated. The host may perform this
check in both IPv6-only and dual-stack access networks.
When sending AAAA query for the known name a host MUST set "Checking
Disabled (CD)" bit to zero, as otherwise the DNS64 will not perform
IPv6 address synthesis hence does not reveal the IPv6 prefix(es) used
for protocol translation.
A DNS reply with one or more non-empty AAAA records indicates that
the access network is utilizing IPv6 address synthesis. A host MUST
look through all of the received AAAA records to collect all
available prefixes. The prefixes may include Well-Known Prefix or
one or more Network-Specific Prefixes. In the case of NSPs the host
SHALL search for the IPv4 address inside of the received IPv6
addresses to determine used address format.
An IPv4 address inside synthesized IPv6 address should be found at
some of the locations described in [RFC6052]. If the searched IPv4
address is not found on any of the standard locations the network
must be using different formatting. In such case the host may try to
find out the IPv4 address at some other location.
The host should ensure a 32-bit IPv4 address value is present only
once in an IPv6 address. In case another instance of the value is
found inside the IPv6, the host shall repeat the search with another
IPv4 address.
In the case only one IPv6 prefix was present in the DNS response: a
host shall use that IPv6 prefix for both local synthetization and for
detecting synthesis done by the DNS64 entity on the network.
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In the case multiple IPv6 prefixes were present in the DNS response:
a host SHOULD use all received prefixes when determining whether
other received IPv6 addresses are synthetic. However, for selecting
prefix for the local IPv6 address synthesis host MUST use the
following prioritization order, of which purpose is to avoid use of
prefixes containing suffixes reserved for the future [RFC6052]:
1. Use NSP having /96 prefix
2. Use WKP prefix
3. Use longest available NSP prefix
In the case of NXDOMAIN or empty AAAA reply: the DNS64 is not
available on the access network, network filtered the well-known AAAA
query on purpose, or something went wrong in the DNS resolution. All
unsuccesful cases result in unavailability of a host to perform local
IPv6 address synthesis. The host MAY periodically resend AAAA query
to check if DNS64 has become available or temporary problem cleared.
The host MAY also continue monitoring DNS replies with IPv6 addresses
constructed from WKP, in which case the host MAY use the WKP as if it
were learned during the query for well-known name.
3.1. Connectivity test
After the host has obtained a candidate prefix and format for the
IPv6 address synthesis it may locally synthesize an IPv6 address, by
using a publicly routable IPv4 address, and test connectivity with
the resulting IPv6 address. The connectivity test may be conducted
e.g. with ICMPv6 or with a transport layer protocol. The used public
IPv4 address may be learned via separate A query.
This connectivity test ensures local address synthetization results
in functional and protocol translatable IPv6 addresses.
3.2. IPv4 addresses of the known name
The IPv4 addresses of the known name should be such that they are
unlikely to appear more than once within an IPv6 address and also as
easy as possible to find from within the synthetic IPv6 address.
Good addresses might be 127.127.127.127 as a primary and
192.168.127.254 as a secondary. The secondary address is needed in
the case multiple instaces of primary address are present in a
synthetic IPv6 address. The IPv4 addresses can, however, be publicly
routable especially if also used for the connectivity test.
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3.3. Non-standard IPv6 address formats
A node may need to perform more complex heuristics to cope with
networks possibly using non-standard IPv6 address formats. Non-
standard approaches might include for example:
1. Non-standard location: IPv4 address in one piece at non-standard
location. Can be found by pattern matching.
2. Fragmented: IPv4 address in multiple pieces around the IPv6
address. May be found by pattern matching.
3. Obfuscated address: IPv4 address is obfuscated, for example
xorred. May potentially be found especially if standard addess
format is used, but as this is an indication of access network's
unwillingness to support host based synthetization the host
should not try to decipher the IPv6 prefix.
4. Hosting of an IPv4-only name(s)
The required IPv4-only name has to be hosted by someone. While
IANA(?) might host one (?), it may be safest for device, operating
system, and/or application vendors to host IPv4-only names for their
own uses. The name should have two A records in order to manage in
situations where the first IPv4 address appears more than once within
synthetic IPv6 address. Another name may be needed for connectivity
test purposes.
5. Required IPv4 addresses
A prefix detection without connectivity test does not require any
routable IPv4 addresses. The connectivity test requires a routable
IPv4 address on the server side.
6. Security Considerations
No security considerations have been identified.
7. IANA Considerations
IANA(?) should define a name and an IPv4 address for a Well-Known
IPv4-only Name.
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8. Acknowledgements
Authors would like to thank Dan Wing, Washam Fan, Cameron Byrne, and
Christian Huitema for improvement ideas and comments.
9. Normative References
[I-D.ietf-behave-dns64]
Bagnulo, M., Sullivan, A., Matthews, P., and I. Beijnum,
"DNS64: DNS extensions for Network Address Translation
from IPv6 Clients to IPv4 Servers",
draft-ietf-behave-dns64-11 (work in progress),
October 2010.
[I-D.ietf-behave-v6v4-xlate-stateful]
Bagnulo, M., Matthews, P., and I. Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers",
draft-ietf-behave-v6v4-xlate-stateful-12 (work in
progress), July 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
Authors' Addresses
Teemu Savolainen
Nokia
Hermiankatu 12 D
FI-33720 Tampere
Finland
Email: teemu.savolainen@nokia.com
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Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
Finland
Email: jouni.nospam@gmail.com
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