Behave WG T. Savolainen
Internet-Draft Nokia
Intended status: Standards Track J. Korhonen
Expires: September 13, 2012 Nokia Siemens Networks
D. Wing
Cisco Systems
March 12, 2012
Discovery of IPv6 Prefix Used for IPv6 Address Synthesis
draft-ietf-behave-nat64-discovery-heuristic-07.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. The method depends on existence of a well-known IPv4-only
domain name "ipv4only.arpa". The information learned enables nodes
to perform local IPv6 address synthesis and to potentially avoid
traversal through NAT64 on dual-stack accesses and multi-interface
deployments.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
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."
This Internet-Draft will expire on September 13, 2012.
Copyright Notice
Copyright (c) 2012 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
publication of this document. Please review these documents
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carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements and Terminology . . . . . . . . . . . . . . . . . 3
2.1. Requirements . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Node Behavior . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Secure Learning of Pref64::/n . . . . . . . . . . . . . . 6
3.1.1. DNSSEC Requirements for the Network . . . . . . . . . 6
3.1.2. Node Behavior . . . . . . . . . . . . . . . . . . . . 6
3.2. Connectivity Check . . . . . . . . . . . . . . . . . . . . 7
3.2.1. No Connectivity Checks Against ipv4only.arpa . . . . . 8
3.3. Alternative Domain Names . . . . . . . . . . . . . . . . . 9
4. Operational Considerations for Hosting the IPv4-Only
Well-Known Name . . . . . . . . . . . . . . . . . . . . . . . 9
5. DNS(64) Entity Considerations . . . . . . . . . . . . . . . . 9
6. Exit Strategy . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. About the IPv4 Address for the Well-Known Name . . . . . . 10
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Example of DNS Record Configuration . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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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 nodes [RFC6144]. The DNS64
utilizes IPv6 address synthesis to create local IPv6 presentations of
peers having only IPv4 addresses, hence allowing DNS-using IPv6-only
nodes 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
nodes running validating DNSSEC enabled DNS resolvers, but instead
the synthesis must be done by the nodes themselves. In order to
perform IPv6 synthesis nodes have to learn the IPv6 prefix(es) used
on the access network for protocol translation. The prefixes, which
may be Network Specific Prefixes (NSP) or Well-Known Prefixes (WKP)
[RFC6052], are referred in this document as Pref64::/n [RFC6146].
This document describes a best effort method for applications and
nodes to learn the information required to perform local IPv6 address
synthesis. The IPv6 address synthesis procedure itself is out-of-
scope of this document. An example application is a browser
encountering IPv4 address literals in an IPv6-only access network.
Another example is a node 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 or if a node is multi-interfaced [RFC6418]. In such cases
nodes may choose to prefer IPv4 or alternative network interface in
order to avoid traversal through protocol translators.
It is important to notice that use of this approach will not result
in as robust, secure, and good behaving system as an all-IPv6 system
would be. Hence it is highly recommended to upgrade nodes'
destinations to IPv6 and utilize the described method only as a
short-term solution.
2. Requirements and Terminology
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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].
2.2. Terminology
NAT64 FQDN: One or more fully qualified domain names for NAT64
protocol translator entity.
Pref64::/n: The IPv6 prefix used on IPv6 address synthesis [RFC6146].
Well-Known IPv4-only Name (WKN): a fully qualified domain name,
"ipv4only.arpa", 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. Node Behavior
A node requiring information about presence of NAT64 and the
Pref64::/n used for protocol translation SHALL send a DNS query for
AAAA records of a well-known IPv4-only fully qualified domain name:
"ipv4only.arpa". The node MAY also need to perform DNS query for the
A record of the well-known name in order to learn what is the IPv4
address of the well-known name and if the A record even exists (see
also Section 6 Exit Strategy). The node may perform this check in
both IPv6-only and dual-stack access networks.
When sending AAAA query for the well-known name a node MUST set
"Checking Disabled (CD)" bit to zero, as otherwise the DNS64 will not
perform IPv6 address synthesis hence does not reveal the Pref64::/n
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 node MUST
look through all of the received AAAA records to collect one or more
Pref64::/n. Pref64::/n list may include Well-Known Prefix 64:
ff9b::/96 [RFC6052] or one or more Network-Specific Prefixes. In the
case of NSPs the node SHALL search for the IPv4 address of the well-
known name inside of the received IPv6 addresses to determine the
used address format.
An IPv4 address of the well-known name should be found inside
synthetic IPv6 address at some of the locations described in
[RFC6052]. If the searched IPv4 address is not found on any of the
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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 node 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 node shall repeat the search with another
IPv4 address, if possible.
In the case only one Pref64::/n was present in the DNS response: a
node shall use that Pref64::/n for both local synthesis and for
detecting synthesis done by the DNS64 entity on the network.
In the case of more than one Pref64::/n were present in the DNS
response: a node SHOULD use all of them when determining whether
other received IPv6 addresses are synthetic. However, for selecting
Pref64::/n for the local IPv6 address synthesis node MUST use the
following prioritization order, of which purpose is to avoid use of
Pref64::/n 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 node to perform
local IPv6 address synthesis. The node MAY periodically resend AAAA
query to check if DNS64 has become available. The node MAY also
continue monitoring for DNS replies with IPv6 addresses constructed
from WKP, in which case the node SHOULD use the WKP as if it were
learned during the query for the well-known name.
To save Internet's resources, if possible, a node should perform
Pref64::/n discovery only when needed (e.g. when local synthesis is
required, cached reply timeouts, new network interface is started,
and so forth). The node SHALL cache the replies it receives during
Pref64::/n discovery procedure and it SHALL repeat the discovery
process when one third of the Time-To-Live of the Well-Known Name's
synthetic AAAA DNS response is remaining.
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3.1. Secure Learning of Pref64::/n
If a node is using insecure channel between itself and DNS64, or
DNS64 entity itself is untrusted, it is possible for an attacker to
influence node's Pref64::/n detection procedures. This may result in
denial-of-service, redirection, man-in-the-middle, or other attacks.
To protect against these attacks the node SHOULD communicate with
trusted DNS64 over secure channel or use DNSSEC. NAT64 operators
SHOULD provide facilities for secure learning of Pref64::/n: a secure
channel and/or DNSSEC protection.
3.1.1. DNSSEC Requirements for the Network
If the operator has chosen to support nodes performing Pref64::/n
learning securely with DNSSEC, the operator of the NAT64 device MUST
perform the following configurations.
1. Have one or more fully qualified domain names for the NAT64
translator entities (later referred as NAT64 FQDN). In the case
of more than one Pref64::/n being used in a network, e.g. for
load-balancing purposes, it is for network administrators to
decide whether a single NAT64's fully qualified domain name maps
to more than one Pref64::/n, or whether there will be dedicated
NAT64 FQDN per Pref64::/n.
2. Each NAT64 FQDN MUST have one or more DNS AAAA resource records
with each IPv6 address consisting of Pref64::/n and 0's for the
elements after the actual prefix.
3. Each Pref64::/n MUST HAVE PTR record that points to corresponding
NAT64 FQDN.
4. Sign the NAT64 FQDNs' AAAA and A records with DNSSEC.
3.1.2. Node Behavior
A node SHOULD prefer secure channel to talk to DNS64, whenever
possible. In addition, a node that implements DNSSEC validating
resolver MAY use the following procedure to secure discovery of the
Pref64::/n.
1. Heuristically find out a Pref64::/n candidate by making AAAA
query for the "ipv4only.arpa" by following the procedure in
Section 3. This will return one or more AAAA resource records.
For each of those AAAA resource records node wishes to use
securely, the node performs the following steps.
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2. Send DNS PTR query for the IPv6 address of the translator (for
"ipv6.arpa"), using the Pref64::/n from the step 1 and zeroes for
the elements after the actual prefix length. This will return
the NAT64 FQDN.
3. The node SHOULD compare the domain of the NAT64 FQDN with node's
list of trusted domains. The means for node to learn the trusted
domains is implementation specific. If the node has no list of
trusted domains, the node MAY query user whether the domain can
be trusted. The node MAY remember the answer for future use. If
the node has no trust for the domain, the discovery procedure is
not secure and remaining steps described below are not needed.
4. Send DNS AAAA query for the NAT64 FQDN.
5. Verify the DNS AAAA response matches the address obtained in step
1. It is possible that the NAT64 FQDN maps to multiple AAAA
records, in which case the node has to check if any of the
responses matches to the address obtained in step 1. The node
must ignore other responses and not to use those for local IPv6
address synthesis.
6. Perform DNSSEC validation of the DNS AAAA response.
After the node has successfully performed the above five steps, the
node can consider Pref64::/n securely learned.
3.2. Connectivity Check
After learning Pref64::/n, the node SHOULD perform connectivity check
to ensure the learned Pref64::/n is functional. It could be non-
functional for a variety of reasons -- the discovery failed to work
as expected, the IPv6 path to the NAT64 is down, the NAT64 is down,
or the IPv4 path beyond the NAT64 is down.
There are two main approaches to determine if the learned Pref64::/n
is functional. The first approach is to perform a dedicated
connectivity check. The second approach is to simply attempt to use
the learned Pref64::/n. Each approach has some trade-offs (e.g.,
additional network traffic or possible user-noticable delay), and
implementations should carefully weight which approach is appropriate
for their application and the network.
The node SHOULD use implementation specific connectivity check
server, but if that is not possible a node MAY do a PTR query of the
Pref64::/n that may return a hostname. The node then does an A query
of that hostname, which may return zero, one or more A resource
records pointing to connectivity check servers used by the network
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operator. Negative response to PTR or A query means there are no
connectivity check servers available. The operator of a NAT64 entity
MAY assist nodes in their connectivity checks by mapping each NAT64
FQDN to one or more DNS A resource records with IPv4 address(es)
pointing to connectivity check server(s).
In case of one or more connectivity check servers being available for
use, the node chooses the first one preferring vendor specific
servers, if multiple are available. The node MAY perform separate
connectivity check by sending an ICMPv6 Echo Request to IPv6 address
synthesized by combining discovered Pref64::/n with an IPv4 address
of the server used for the connectivity check. This will test the
IPv6 path to the NAT64, the NAT64's operation, and the IPv4 path all
the way to the connectivity check server. Alternatively the node MAY
utilize implementation specific connectivity check protocol. If no
response is received for the ICMPv6 Echo Request, the node sends
another ICMPv6 Echo Request, a second later. If still no response is
received, it sends a third ICMPv6 Echo Request 3 seconds later. If
an ICMPv6 Echo Response is received, the node knows the IPv6 path to
the connectivity check server is functioning normally. If, after the
three transmissions of the ICMPv6 Echo Request, no response is
received, the node learns this Pref64::/n may not be functioning, and
the node MAY choose a different NAT64 (if a different NAT64 is
available), choose to alert the user, or proceed anyway hoping the
problem is temporal or only with the connectivity check itself.
If no separate connectivity check is performed before local IPv6
address synthesis, a node may monitor success of connection attempts
performed with locally synthetized IPv6 addresses. Based on success
of these connections, and based on possible ICMPv6 error messages
received (such as Destination Unreachable Message), the mode MAY
cease to perform local address synthesis and MAY restart Pref64::/n
discovery procedures.
3.2.1. No Connectivity Checks Against ipv4only.arpa
Clients MUST NOT send a connectivity check to the address returned in
the ipv4only.arpa query. This is because, by design, no server will
be operated on the Internet at that address as such. Similarly,
network operators MUST NOT operate a server on that address. The
reason this address isn't used for connectivity checks is that
operators who neglect to operate a connectivity check server will
allow that traffic towards the Internet where it will be dropped and
cause a false negative connectivity check with the client (that is,
the NAT64 is working fine, but the connectivity check fails because a
server is not operating at ipv4-only.arpa on the Internet and a
server is not operated by the NAT64 operator). Instead, for the
connectivity check, an additional DNS resource record is looked up
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and used for the connectivity check. This ensures that packets don't
unnecessarily leak to the Internet and reduces the chance of a false
negative connectivity check.
3.3. Alternative Domain Names
Some applications, operating systems, devices, or networks may find
it advantageous to operate their own DNS infrastructure to perform a
function similar to ipv4-only.arpa, but using a different resource
record. The primary advantage is to ensure availability of the DNS
infrastructure and ensure the proper configuration of the DNS record
itself. DNS For example, a company named Example might have their
application query ipv4-only.example.com. Other than the different
DNS resource record being queried, the rest of the operations are
anticipated to be identical to the steps described in this document.
4. Operational Considerations for Hosting the IPv4-Only Well-Known Name
The authoritative name server for the well-known name shall have DNS
record Time-To-Live (TTL) set to a long value in order to improve
effectiveness of DNS caching. The exact TTL value depends on
availability time for the used public IPv4 address.
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 defined and 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.
A node SHOULD implement configuration knob for disabling the
Pref64::/n discovery feature.
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7. Security Considerations
The security considerations follow closely those of RFC6147
[RFC6147]. If an attacker manages to change the Pref64::/n node
discovers, the traffic generated by the node 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
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 nodes' Pref64::/n discovery procedures.
A node SHOULD implement validating DNSSEC resolver for validating the
A response of the well-known name query. A node without validating
DNSSEC resolver SHOULD request validation to be performed by the used
recursive DNS server and use secure channel when communicating with
the DNS64.
For the secure Pref64::/n discovery the access network SHOULD sign
the NAT64 translator's fully qualified domain name. A node SHOULD
use the algorithm described in Section 3.1 in order to securely learn
the Pref64::/n.
Lastly, best mitigation action against Pref64::/n discovery attacks
is to add IPv6 support for nodes' destinations and hence reduce need
to perform local IPv6 address synthesis.
8. IANA Considerations
According to procedures described in RFC3172 this document requests
IANA and IAB to reserve a second level domain from the .ARPA zone for
the well-known domain name. The well-known domain name could be, for
example, "ipv4only.arpa".
The well-known name also needs to map to one but preferably to two
different public IPv4 addresses.
8.1. About the IPv4 Address for the Well-Known Name
The IPv4 address for the well-known name, 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. An address not listed in the Section 3 of
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[RFC5735] is required as otherwise DNS64 entity may not perform AAAA
record synthesis. The address does not have to be routable or
allocated to any node, 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 statically 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 Cameron Byrne, Christian Huitema, Washam
Fan, Peter Koch, Stephan Lagerholm, Zhenqiang Li, Andrew Sullivan,
and Dave Thaler, for significant improvement ideas and comments.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
BCP 153, RFC 5735, January 2010.
[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.
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10.2. Informative References
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
[RFC6418] Blanchet, M. and P. Seite, "Multiple Interfaces and
Provisioning Domains Problem Statement", RFC 6418,
November 2011.
Appendix A. Example of DNS Record Configuration
The following BIND-style examples illustrate how A and AAAA records
could be configured by NAT64 operator.
The examples use Pref64::/n of 2001:db8::/96 and example.com domain.
The PTR record for reverse queries (Section 3.1.1 bullet 3):
$ORIGIN 0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.0.8.b.d.0.1.0.0.2.IP6.ARPA.
@ IN SOA ns1.example.com. hostmaster.example.com. (
2003080800 12h 15m 3w 2h)
IN NS ns.example.com.
IN PTR nat64.example.com.
If the example.com does not use DNSSEC, the following configuration
file could be used. Please note the nat64.example.com has both AAAA
record with the Pref64::/n and A record for the connectivity check
(Section 3.1.1 bullet 2).
example.com. IN SOA ns.example.com. hostmaster.example.com. (
2002050501 ; serial
100 ; refresh (1 minute 40 seconds)
200 ; retry (3 minutes 20 seconds)
604800 ; expire (1 week)
100 ; minimum (1 minute 40 seconds)
)
example.com. IN NS ns.example.com.
nat64.example.com.
IN AAAA 2001:db8:0:0:0:0:0 nat64.example.com.
IN A 192.0.2.1
If the example.com does use DNSSEC, the following configuration file
could be used for A and AAAA records:
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example.com. IN SOA ns.example.com. hostmaster.example.com. (
2002050501 ; serial
100 ; refresh (1 minute 40 seconds)
200 ; retry (3 minutes 20 seconds)
604800 ; expire (1 week)
100 ; minimum (1 minute 40 seconds)
)
example.com. IN RRSIG SOA 5 2 100 20090803071330 (
20090704071330 17000 example.com.
TVgWsNQvsFmeNHAeccGi7+UI7KwcE9TXPuSvmV9yyJwo
4FvHkxVC1H+98EtrmbR4c/XcdUzdfgn+q+lBqNsnbAit
xFERwPxzxbX0+yeCdHbBjHe7OuOc2Gc+CH6SbT2lKwVi
iEx3ySqqNoVScoUyhRdnPV2A1LV0yd9GtG9mI4w= )
example.com. IN NS ns.example.com.
example.com. IN RRSIG NS 5 2 100 20090803071330 (
20090704071330 17000 example.com.
Xuw7saDDi6+5Z7SmtC7FC2npPOiE8F9qMR87eA0egG0I
B+xFx7pIogoVIDpOd1h3jqYivhblpCoDSBQb2oMbVy3B
SX5cF0r7Iu/xKP8XrV4DjNiugpa+NnhEIaRqG5uoPFbX
4cYT51yNq70I5mJvvajJu7UjmdHl26ZlnK33xps= )
nat64.example.com.
IN AAAA 2001:db8:0:0:0:0:0 nat64.example.com.
IN RRSIG SOA 5 2 100 20090803071330 (
20090704071330 17000 example.net.
TVgWsNQvsFmeNHAeccGi7+UI7KwcE9TXPuSvmV9yyJwo
4FvHkxVC1H+98EtrmbR4c/XcdUzdfgn+q+lBqNsnbAit
xFERwPxzxbX0+yeCdHbBjHe7OuOc2Gc+CH6SbT2lKwVi
iEx3ySqqNoVScoUyhRdnPV2A1LV0yd9GtG9mI4w= )
nat64.example.com.
IN A 192.0.2.1
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
Dan Wing
Cisco Systems
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
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