Behave WG T. Savolainen
Internet-Draft Nokia
Intended status: Standards Track J. Korhonen
Expires: December 31, 2012 Nokia Siemens Networks
D. Wing
Cisco Systems
June 29, 2012
Discovery of IPv6 Prefix Used for IPv6 Address Synthesis
draft-ietf-behave-nat64-discovery-heuristic-10.txt
Abstract
This document describes a method for detecting the presence of DNS64
and for learning the IPv6 prefix used for protocol translation on an
access network. The method depends on the 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 NAT64 on dual-stack 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
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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 December 31, 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
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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. Validation of Discovered Pref64::/n . . . . . . . . . . . 6
3.1.1. DNSSEC Requirements for the Network . . . . . . . . . 6
3.1.2. DNSSEC Requirements for the Node . . . . . . . . . . . 7
3.2. Connectivity Check . . . . . . . . . . . . . . . . . . . . 8
3.2.1. No Connectivity Checks Against ipv4only.arpa . . . . . 9
3.3. Alternative Domain Names . . . . . . . . . . . . . . . . . 10
3.4. Message Flow Illustration . . . . . . . . . . . . . . . . 10
4. Operational Considerations for Hosting the IPv4-Only
Well-Known Name . . . . . . . . . . . . . . . . . . . . . . . 12
5. Operational Considerations for DNS64 Operator . . . . . . . . 12
5.1. Mapping of IPv4 Address Ranges to IPv6 Prefixes . . . . . 12
6. Exit Strategy . . . . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 15
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
10.1. Normative References . . . . . . . . . . . . . . . . . . . 15
10.2. Informative References . . . . . . . . . . . . . . . . . . 16
Appendix A. Example of DNS Record Configuration . . . . . . . . . 16
Appendix B. About the IPv4 Address for the Well-Known Name . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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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]. DNS64
utilizes IPv6 address synthesis to create local IPv6 addresses for
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 addresses that would be translated
to the 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 a 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 used in dual-stack enabled access
networks or if a node is multi-interfaced [RFC6418]. In such cases,
nodes may choose to prefer IPv4 or an alternative network interface
in order to avoid traversal through protocol translators.
It is important to note that use of this approach will not result in
a system that is as robust, secure, and well-behaved 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
transition 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: a fully qualified domain name for a NAT64 protocol
translator.
Pref64::/n: the IPv6 prefix used for IPv6 address synthesis
[RFC6146].
Pref64::WKA/n: the IPv6 address consisting of Pref64::/n and WKA at
any of the locations allowed by RFC 6052 [RFC6052].
Well-Known IPv4-only Name (WKN): a fully qualified domain name,
"ipv4only.arpa", well-known to have only A record(s).
Well-Known IPv4 Address (WKA): an IPv4 address that is well-known and
present in an A record for the well-known name. Two well-known IPv4
addresses are defined for the Pref64::/n discovery purposes:
192.0.0.170 and 192.0.0.171.
3. Node Behavior
A node requiring information about the presence (or absence) of
NAT64, and the Pref64::/n used for protocol translation SHALL send a
DNS query for AAAA resource records of the Well-Known IPv4-only Name
(WKN) "ipv4only.arpa". The node MAY perform the DNS query in both
IPv6-only and dual-stack access networks.
When sending a DNS AAAA resource record query for the WKN, a node
MUST set the "Checking Disabled (CD)" bit to zero [RFC4035], as
otherwise the DNS64 server will not perform IPv6 address synthesis
(Section 3 of [RFC6147]) and hence would not reveal the Pref64::/n
used for protocol translation.
A DNS reply with one or more AAAA resource records indicates that the
access network is utilizing IPv6 address synthesis. In some
scenarios NXDOMAIN and NXRRSET hijacking performed by the access
network may result in a false positive. One method to detect such
hijacking is to query a Fully Qualified Domain Name (FQDN) that is
known to be invalid (and normally return an empty response or an
error response) and see if it returns a valid resource record.
However, as long as the hijacked domain does not result in AAAA
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resource record responses that contain well-known IPv4 address in any
location defined by RFC6052, the response will not disturb Pref64::/n
learning procedure.
A node MUST look through all of the received AAAA resource records to
collect one or more Pref64::/n. The Pref64::/n list might include
the Well-Known Prefix 64:ff9b::/96 [RFC6052] or one or more Network-
Specific Prefixes. In the case of NSPs, the node SHALL determine the
used address format by searching the received IPv6 addresses for the
WKN's well-known IPv4 addresses. The node SHALL assume the well-
known IPv4 addresses might be found at the locations specified by
RFC6052 section 2.2. If the well-known IPv4 addresses are not found
within the standard locations, it indicates that the network is not
using standard address format and the Pref64::/n cannot be
determined. Developers can over time learn of 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 procedure. The additional steps are outside the
scope of the present document.
In case a node does not receive positive DNS reply to AAAA resource
record query, the node MAY perform DNS A resource record query for
the well-known name. If the node receives positive reply to the DNS
A resource record query it means the used recursive DNS server is not
DNS64 server.
The node MUST ensure a 32-bit well-known IPv4 address value is
present only once in an IPv6 address. In case another instance of
the value is found inside the IPv6 address, the node SHALL repeat the
search with the other well-known IPv4 address.
If 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 server on the network.
If more than one Pref64::/n was present in the DNS response: a node
SHOULD use all of them when determining whether other received IPv6
addresses are synthetic. The node MUST use all learned Pref64::/n
when performing local IPv6 address synthesis, and use the prefixes in
the order received from DNS64 server. That is, when the node is
providing a list of locally synthesized IPv6 addresses to upper
layers, IPv6 addresses MUST be synthesized by using all discovered
Pref64::/n in the received order.
In the case of a negative response (NXDOMAIN, NXRRSET) or a DNS query
timeout: a DNS64 server is not available on the access network, the
access network filtered out the well-known query, or something went
wrong in the DNS resolution. All unsuccessful cases result in a node
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being unable to perform local IPv6 address synthesis. In the case of
timeout, the node SHOULD retransmit the DNS query like any other DNS
query the node makes [RFC1035]. In the case of a negative response
(NXDOMAIN, NXRRSET), the node MUST obey the Time-To-Live [RFC1035] of
the response before resending the AAAA resource record query. The
node MAY monitor for DNS replies with IPv6 addresses constructed from
the WKP, in which case if any are observed the node SHOULD use the
WKP as if it were learned during the query for the well-known name.
To save Internet resources if possible, a node should perform
Pref64::/n discovery only when needed (e.g., when local synthesis is
required, a new network interface is connected to a new network, and
so forth). The node SHALL cache the replies it receives during the
Pref64::/n discovery procedure and it SHOULD repeat the discovery
process ten seconds before the Time-To-Live of the Well-Known Name's
synthetic AAAA resource record expires.
3.1. Validation of Discovered Pref64::/n
If a node is using an insecure channel between itself and a DNS64
server, or the DNS64 server is untrusted, it is possible for an
attacker to influence the node's Pref64::/n discovery procedures.
This may result in denial-of-service, redirection, man-in-the-middle,
or other attacks.
To mitigate against attacks, the node SHOULD communicate with a
trusted DNS64 server over a secure channel, or use DNSSEC. NAT64
operators SHOULD provide facilities for validating discovery of
Pref64::/n via a secure channel and/or DNSSEC protection.
It is important to understand that DNSSEC only validates that the
discovered Pref64::/n is the one that belongs to a domain used by
NAT64 FQDN. Importantly, the DNSSEC validation does not tell if the
node is at the network where the Pref64::/n is intended to be used.
Furthermore, DNSSEC validation cannot be utilized in the case of WKP.
3.1.1. DNSSEC Requirements for the Network
If the operator has chosen to support nodes performing validation of
discovered Pref64::/n 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 a dedicated
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NAT64 FQDN per Pref64::/n.
2. Each NAT64 FQDN MUST have one or more DNS AAAA resource records
containing Pref64::WKA/n (Pref64::/n combined with WKA).
3. Each Pref64::WKA/n MUST have a PTR resource record that points to
the corresponding NAT64 FQDN.
4. Sign the NAT64 FQDNs' AAAA and A resource records with DNSSEC.
3.1.2. DNSSEC Requirements for the Node
A node SHOULD prefer a secure channel to talk to a DNS64 server,
whenever possible. In addition, a node that implements a DNSSEC
validating resolver MAY use the following procedure to validate
discovery of the Pref64::/n.
1. Heuristically find Pref64::/n candidates by making a AAAA
resource record query for "ipv4only.arpa" by following the
procedure in Section 3. This will result in IPv6 addresses
consisting of Pref64::/n combined with WKA, i.e. in Pref64::
WKA/n. For each Pref64::/n that the node wishes to validate, the
node performs the following steps.
2. Send DNS PTR resource record query for the IPv6 address of the
translator (for "ip6.arpa"), using the Pref64::WKA/n learned on
the step 1. CNAME and DNAME results should be followed according
to the rules in RFC 1034 [RFC1034], RFC 1034 [RFC1035], and RFC
6672 [RFC6672]. The ultimate response will include one or more
NAT64 FQDNs.
3. The node SHOULD compare the domains of learned NAT64 FQDNs to a
list of the node's trusted domains and choose a NAT64 FQDN that
matches. 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 the user whether the domain can be
trusted and MAY remember the answer for future use. If the node
has no trust for the domain, the discovery procedure is not
secure and the remaining steps described below MUST NOT be
performed.
4. Send a DNS AAAA resource record query for the NAT64 FQDN.
5. Verify the DNS AAAA resource record contains Pref64::WKA/n
addresses received at the step 1. It is possible that the NAT64
FQDN has multiple AAAA records, in which case the node MUST check
if any of the addresses matches the ones obtained in step 1. The
node MUST ignore other responses and not use them for local IPv6
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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 validated.
3.2. Connectivity Check
After learning a Pref64::/n, the node SHOULD perform a 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 weigh which approach is appropriate
for their application and the network.
The node SHOULD use a implementation-specific connectivity check
server and a protocol of the implementation's choice, but if that is
not possible, a node MAY do a PTR resource record query of the
Pref64::WKA/n to get a NAT64 FQDN. The node then does an A resource
query of the NAT64 FQDN, which will return zero or more A resource
records pointing to connectivity check servers used by the network
operator. A negative response to the PTR or A resource query means
there are no connectivity check servers available. A network
operator that provides NAT64 services for a mix of nodes with and
without implementation-specific connectivity check servers SHOULD
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). The Pref64::/n -based connectivity
check approach works only with NSP, as it is not possible to register
A record for each different domain using WKP. The network operator
MUST disable ICMPv6 rate limiting for connectivity check mesages.
In case of multiple connectivity check servers being available for
use, the node chooses the first one, preferring implementation-
specific servers.
The connectivity check protocol used with implementation-specific
connectivity check servers is implementation-specific.
The connectivity check protocol used with connectivity check servers
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pointed to by NAT64 FQDN's A resource records is ICMPv6 [RFC4443].
The node performing a connectivity check against these servers SHALL
send an ICMPv6 Echo Request to an IPv6 address synthesized by
combining discovered Pref64::/n with an IPv4 address of the server as
specified in RFC6052. 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. If no response is received for the ICMPv6 Echo
Request, the node SHALL send another ICMPv6 Echo Request, a second
later. If still no response is received, the node SHALL send a third
ICMPv6 Echo Request two 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
and three seconds since the last ICMPv6 Echo Request, no response is
received, the node learns this Pref64::/n might not be functioning,
and the node MAY choose a different Pref64::/n (if a different are
available), choose to alert the user, or proceed anyway hoping the
problem is temporal or only with the connectivity check itself.
After all, the ICMPv6 is by design unreliable and failure to receive
ICMPv6 responses may not indicate anything else than network failure
to transport ICMPv6 messages through.
If no separate connectivity check is performed before local IPv6
address synthesis, a node MAY monitor success of connection attempts
performed with locally synthesized IPv6 addresses. Based on success
of these connections, and based on possible ICMPv6 error messages
received (such as Destination Unreachable Message), the node 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 "ipv4only.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
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.
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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 "ipv4only.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. For example, a company named Example might have their
application query "ipv4only.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.
3.4. Message Flow Illustration
A figure below gives an example illustration of a message flow in the
case of prefix discovery utilizing Pref64::/n validation. The figure
shows also a step where the procedure ends if no Pref64::/n
validation is performed.
In this example, three Pref64::/n are provided by the DNS64 server.
The first Pref64::/n is using NSP, in this example "2001:db8:
42::/96". The second Pref64::/n is using NSP, in this example "2001:
db8:43::/96". The third Pref64::/n is using WKP. Hence, when the
Pref64::/n are combined with WKA to form Pref64::WKA/n, the synthetic
IPv6 addresses returned by DNS64 server are "2001:db8:42::
192.0.0.170", "2001:db8:43::192.0.0.170", and "64:ff9b::192.0.0.170".
The synthetic addresses could also contain the IPv4 address
192.0.0.171.
The validation is not done for the WKP, see Section 3.1.
Node DNS64 server
| |
| "AAAA" query for "ipv4only.arpa" |
|----------------------------------------------->| "A" query for
| | "ipv4only.arpa"
| |---------------->
| |
| | "A" response:
| | "192.0.0.170"
| | "192.0.0.171"
| |<----------------
| +----------------------------+
| | "AAAA" synthesis using |
| | three Pref64::/n. |
| +----------------------------+
| "AAAA" response with: |
| "2001:db8:42::192.0.0.170" |
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| "2001:db8:43::192.0.0.170" |
| "64:ff9b::192.0.0.0170" |
|<-----------------------------------------------|
| |
+----------------------------------------------+ |
| If Pref64::/n validation is not performed, a | |
| node can fetch prefixes from AAAA responses | |
| at this point and skip the steps below. | |
+----------------------------------------------+ |
| |
| "PTR" query #1 for "2001:db8:42::192.0.0.170 |
|----------------------------------------------->|
| "PTR" query #2 for "2001:db8:43::192.0.0.170 |
|----------------------------------------------->|
| |
| "PTR" response #1 "nat64_1.example.com" |
|<-----------------------------------------------|
| "PTR" response #2 "nat64_2.example.com" |
|<-----------------------------------------------|
| |
+----------------------------------------------+ |
| Compare received domains to a trusted domain | |
| list and if matches are found, continue. | |
+----------------------------------------------+ |
| |
| "AAAA" query #1 for "nat64_1.example.com" |
|----------------------------------------------->|
| "AAAA" query #2 for "nat64_2.example.com" |
|----------------------------------------------->|
| |
| "AAAA" resp. #1 with "2001:db8:42::192.0.0.170 |
|<-----------------------------------------------|
| "AAAA" resp. #2 with "2001:db8:43::192.0.0.170 |
|<-----------------------------------------------|
| |
+----------------------------------------------+ |
| Validate AAAA responses and compare the IPv6 | |
| addresses to those previously learned. | |
+----------------------------------------------+ |
| |
+----------------------------------------------+ |
| Fetch the Pref64::/n from the validated | |
| responses and take into use. | |
+----------------------------------------------+ |
| |
Pref64::/n discovery procedure
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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 at least 60 minutes in order to
improve effectiveness of DNS caching. The exact TTL value will be
determined and tuned based on operational experiences.
The domain serving the well-known name MUST be signed with DNSSEC.
See also section 7.
5. Operational Considerations for DNS64 Operator
A network operator of DNS64 server can guide nodes utilizing
heuristic discovery procedures by managing the responses DNS64 server
provides.
If the network operator would like nodes to utilize multiple
Pref64::/n, the operator needs to configure DNS64 server to respond
with multiple synthetic AAAA records. As per section Section 3 the
nodes can then use them all.
There are no guarantees on what of the Pref64::/n nodes will end up
using. If the operator wants nodes to specifically use certain
Pref64::/n or periodically change the Pref64::/n they use, for
example for load balancing reasons, the only guaranteed method is to
make DNS64 server to return only single synthetic AAAA resource
record, and have Time-To-Live of that synthetic record such that node
repeats the Pref64::/n discovery when required Section 3.
Besides choosing how many Pref64::/n to respond and what Time-To-Live
to use, DNS64 servers MUST NOT interfere with or perform other
special procedures for the queries related to the well-known name.
5.1. Mapping of IPv4 Address Ranges to IPv6 Prefixes
The RFC 6147 [RFC6147] allows DNS64 implementations to be able to map
specific IPv4 address ranges to separate Pref64::/n. That allows
handling of special use IPv4 addresses [RFC5735]. The example setup
where this might be used is illustrated in Figure 1. The NAT64 "A"
is used when accessing IPv4-only servers in the datacenter, and the
NAT64 "B" is used for Internet access.
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NAT64 "A" ----- IPv4-only servers in a datacenter
/
IPv6-only node----<
\
NAT64 "B" ----- IPv4 Internet
Figure 1: NAT64s with IPv4 Address Ranges
The heuristic discovery method described herein does not support
learning of the possible rules used by DNS64 server for mapping
specific IPv4 address ranges to separate Pref64::/n. Therefore,
nodes will use the same discovered Pref64::/n to synthesize IPv6
addresses out from any IPv4 address. This can cause issues for
routing and connectivity establishment procedures. The operator of
the NAT64 and the DNS64 ought to take this into account in the
network design.
The network operators can help IPv6-only nodes by ensuring the nodes
do not have to work with IPv4 address literals for which special
mapping rules are used. That is, the IPv4-only servers addressed
from the special IPv4 address ranges ought to have signed AAAA
records, which allows IPv6-only nodes to avoid local address
synthesis. If the IPv6-only nodes are not using DNSSEC, then it is
enough if the network's DNS64 server returns synthetic AAAA resource
records pointing to IPv4-only servers. Avoiding the need for IPv6-
only node to perform address synthesis for IPv4 addresses belonging
to special ranges is the best approach to assist nodes.
If the IPv6-only nodes have no other choice than use IPv4-address
literals belonging to special IPv4 address ranges, and the IPv6-only
node will perform local synthesis by using the discovered Pref64::/n,
then the network ought to ensure with routing that the packets are
delivered to the correct NAT64. For example, a router in the path
from IPv6-only host to NAT64s can forward the IPv6 packets to correct
NAT64 as illustrated in Figure 2. The routing could be based on the
last 32-bits of the IPv6 address, but the network operator can also
use some other IPv6 address format allowed by RFC 6052 [RFC6052], if
it simplifies routing setup. This setup requires additional logic on
the NAT64 providing connectivity to special IPv4 address ranges: it
needs to be able to translate packets it receives that are using the
Pref64::/n used with Internet connections.
NAT64 "A" ----- IPv4-only servers in a datacenter
/
IPv6-only host----router
\
NAT64 "B" ----- IPv4 Internet
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Figure 2: NAT64s with Assisting Router
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 a configuration knob for disabling the
Pref64::/n discovery feature.
7. Security Considerations
The security considerations follow closely those of RFC 6147
[RFC6147]. The possible attacks are very similar in the case where
attacker controls DNS64 server and returns tampered IPv6 addresses to
a node and in the case where attacker causes the node to use tampered
Pref64::/n for local address synthesis. The DNSSEC cannot be used to
validate responses created by a DNS64 server the node has no trust
relationship with. Hence this document does not change the big
picture for untrusted network scenarios. If an attacker mangles with
Pref64::/n used by a DNS64 server or a node, the traffic generated by
the node will be delivered to an 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 a target for attackers who
wish to alter nodes' Pref64::/n discovery procedures.
A node SHOULD implement a validating DNSSEC resolver for validating
the A response of the well-known name query. A node without a
validating DNSSEC resolver SHOULD request validation to be performed
by the recursive DNS server and use a secure channel when
communicating with the DNS64 server.
For Pref64::/n discovery validation, 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 validate
discovered Pref64::/n.
Lastly, the best mitigation action against Pref64::/n discovery
attacks is to add IPv6 support for nodes' destinations and hence
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reduce the need to perform local IPv6 address synthesis.
8. IANA Considerations
According to procedures described in RFC3172 this document requests
IANA 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 needs to map to two different global IPv4
addresses. The addresses are to be taken from the 192.0.0.0/24
address block, and can be, for example 192.0.0.170 and 192.0.0.171.
The addresses are to be documented to be of global scope, but they do
not need to be routable in local or global scopes.
9. Acknowledgements
Authors would like to thank Dmitry Anipko, Cameron Byrne, Aaron Yi
Ding Christian Huitema, Washam Fan, Peter Koch, Stephan Lagerholm,
Zhenqiang Li, Simon Perreault, Marc Petit-Huguenin, Andrew Sullivan,
and Dave Thaler, for significant improvement ideas and comments.
10. References
10.1. Normative References
[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control
Message Protocol (ICMPv6) for the Internet Protocol
Version 6 (IPv6) Specification", RFC 4443, March 2006.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
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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.
[RFC6672] Rose, S. and W. Wijngaards, "DNAME Redirection in the
DNS", RFC 6672, June 2012.
10.2. Informative References
[RFC5735] Cotton, M. and L. Vegoda, "Special Use IPv4 Addresses",
BCP 153, RFC 5735, January 2010.
[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 a NAT64 operator.
The examples use Pref64::/n of 2001:db8::/96 and the 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 example.com does not use DNSSEC, the following configuration file
could be used. Please note tat nat64.example.com has both an AAAA
record with the Pref64::/n and an A record for the connectivity check
(Section 3.1.1 bullet 2).
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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 NS ns.example.com.
nat64.example.com.
IN AAAA 2001:db8:0:0:0:0:0:0
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
Appendix B. About the IPv4 Address for the Well-Known Name
The IPv4 addresses for the well-known name cannot be non-global IPv4
addresses as listed in the Section 3 of [RFC5735]. Otherwise DNS64
servers might not perform AAAA record synthesis when the well-known
prefix is used, as stated in Section 3.1 of [RFC6052]. However, the
addresses do not have to be routable or allocated to any real node,
as no communications will be initiated to these IPv4 address.
Allocation of at least two IPv4 addresses improves the heuristics in
cases where the bit pattern of the primary IPv4 address appears more
than once in the synthetic IPv6 address (NSP prefix contains the same
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bit pattern as the IPv4 address).
If no well-known IPv4 addresses would be statically allocated for
this method, the heuristic would require sending of an additional A
query to learn the IPv4 addresses that would be then searched from
inside of the received IPv6 address.
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
Dan Wing
Cisco Systems
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
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