Behave WG T. Savolainen
Internet-Draft Nokia
Intended status: Standards Track J. Korhonen
Expires: April 16, 2012 Nokia Siemens Networks
October 14, 2011
Discovery of a Network-Specific NAT64 Prefix using a Well-Known Name
draft-ietf-behave-nat64-discovery-heuristic-03.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 well-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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 16, 2012.
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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
4. Operational considerations for hosting the IPv4-only
well-known name . . . . . . . . . . . . . . . . . . . . . . . . 6
5. DNS(64) entity considerations . . . . . . . . . . . . . . . . . 6
6. Exit strategy . . . . . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
8.1. About the IPv4 address for the well-known name . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
10. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
As part of the transition to IPv6 NAT64 [RFC6146] and DNS64 [RFC6147]
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
synthesis must be done by the hosts themselves. 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 applications and
hosts to learn the information required to perform local IPv6 address
synthesis. An example application is a browser encountering IPv4
address literals in an IPv6-only access network. Another example is
a host running validating security aware DNS resolver in an IPv6-only
access network.
The knowledge of IPv6 address synthesis taking place may also be
useful if DNS64 and NAT64 are present in dual-stack enabled access
networks. In such cases hosts may choose to prefer IPv4 in order to
avoid traversal through protocol translators.
It is important to notice that use of this approach will not result
in as robust and good behaving system as an all-IPv6 system would be.
Hence it is highly RECOMMENDED to upgrade to IPv6 and utilize the
described method only as a short-term solution.
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
Well-Known IPv4-only Name (WKN): a fully qualified domain name well-
known to have only A record.
Well-Known IPv4 Address: an IPv4 address that is well-known and
mapped to the well-known name.
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 well-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 64:
ff9b::/96 [RFC6052] 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. Developers may over time learn
on IPv6 translated address formats that are extensions or
alternatives to the standard formats. Developers MAY at that point
add additional steps to the described discovery procedures. The
additional steps are outside the scope of the present document.
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, if possible.
In the case only one IPv6 prefix was present in the DNS response: a
host shall use that IPv6 prefix for both local synthesis and for
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detecting synthesis done by the DNS64 entity on the network.
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 response or an empty AAAA reply: the DNS64 is
not available on the access network, network filtered the well-known
query on purpose, or something went wrong in the DNS resolution. All
unsuccessful 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 possibly temporary
problem cleared. The host MAY perform A query for the well-known
name to learn whether the service is available at all (see section 6
about Exit Strategy). 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.
To save Internet's resources, if possible, a host should perform
NAT64 discovery only when needed (e.g. when local synthesis is
required, cached reply timeouts, new network interface is started,
and so forth. Furthermore, the host SHOULD cache the replies it
receives and honor TTLs.
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.
This connectivity test ensures local address synthesis results in
functional and protocol translatable IPv6 addresses.
The host MUST NOT perform connectivity test for the well-known IPv4
address of the well-known name, but instead to some other destination
such as host vendor servers.
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In many scenarios separate connectivity test is not really required
as an application may just try to connect to the IPv4-only
destination with synthetic IPv6 address and see if a connection is
successfully established or not.
4. Operational considerations for hosting the IPv4-only well-known name
The authoritative name server for the well-known name shall have DNS
record TTL set to a long value in order to improve effectiveness of
DNS caching and robustness of the discovery procedure in general.
The exact value depends on availability time for the used public IPv4
address, but should not be longer than one year.
The domain serving the well-known name must be signed with DNSSEC.
See also Security Considerations section.
It is expected that volumes for well-known name related queries are
roughly SOMETHING, TBD. The infrastructure required to serve well-
known name is SOMETHING, TBD.
5. DNS(64) entity considerations
DNS(64) servers MUST NOT interfere or perform special procedures for
the queries related to the well-known name until the time has arrived
for the exit strategy to be deployed.
6. Exit strategy
A day will come when this tool is no longer needed. At that point
best suited techniques for implementing exit strategy will be
documented. In the global scope the exit strategy may include
sending NXDOMAIN replies by the authoritative name server of the
well-known name with a very long TTL.
A client implementation receiving NXDOMAIN response for the A query
of the well-known name means SHOULD consider this tool as disabled.
7. Security Considerations
The security considerations follow closely those of RFC6147
[RFC6147]. If an attacker manages to change the NSP prefix host
discovers, the traffic generated by the host will be delivered to
altered destination. This can result in either a denial-of-service
(DoS) attack (if the resulting IPv6 addresses are not assigned to any
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device), a flooding attack (if the resulting IPv6 addresses are
assigned to devices that do not wish to receive the traffic), or an
eavesdropping attack (in case the altered NSP is routed through the
attacker).
The zone serving the well-known name has to be protected with DNSSEC,
as otherwise it will be too attractive target for attackers who wish
to alter hosts' NSP prefix discovery procedures.
A host SHOULD implement validating DNSSEC resolver for validating the
A response of the well-known name query. A host without validating
DNSSEC resolver SHOULD request validation to be performed by the used
recursive DNS server.
8. IANA Considerations
A well-known name should be defined and a public IPv4 address
allocated (by IANA? IETF? Someone else?).
8.1. About the IPv4 address for the well-known name
The global IPv4 address for the well-known, if possible, should be
chosen so that it is unlikely to appear more than once within an IPv6
address and also as easy as possible to find from within the
synthetic IPv6 address. A global address is required as otherwise
DNS64 entity will not perform AAAA record synthesis. The address
does not have to be routable as no communications are initiated to
the IPv4 address.
Allocating two IPv4 addresses would improve the heuristics in cases
where the primary IPv4 address' bit pattern appears more than once in
the synthetic IPv6 address (NSP prefix contains the same bit pattern
as the IPv4 address).
If no well-known IPv4 address is allocated for this method, the
heuristic requires sending additional A query to learn the IPv4
address that is sought inside the received IPv6 address. Without
knowing IPv4 address it is impossible to determine address format
used by DNS64.
9. Acknowledgements
Authors would like to thank Andrew Sullivan, Dan Wing, Washam Fan,
Cameron Byrne, Zhenqiang Li, Dave Thaler, and Christian Huitema for
significant improvement ideas and comments.
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10. Normative References
[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.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
Authors' Addresses
Teemu Savolainen
Nokia
Hermiankatu 12 D
FI-33720 Tampere
Finland
Email: teemu.savolainen@nokia.com
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
FI-02600 Espoo
Finland
Email: jouni.nospam@gmail.com
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