Behavior Engineering for Hindrance R. Penno
Avoidance T. Saxena
Internet-Draft Juniper Networks
Intended status: Informational D. Wing
Expires: August 25, 2010 Cisco Systems
February 21, 2010
Analysis of 64 Translation
draft-penno-behave-64-analysis-03
Abstract
Due to specific problems, NAT-PT was deprecated by the IETF as a
mechanism to perform IPv6/IPv4 translation. Since then, new work has
commenced which standardizes new mechanisms to perform IPv6/IPv4
translation. This document evaluates how the new translation
mechanisms avoid the problems that caused the IETF to deprecate
NAT-PT.
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].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF), its areas, and its working groups. Note that
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This Internet-Draft will expire on August 25, 2010.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Analysis of 64 Translation Against Concerns of RFC4966 . . . . 4
2.1. Problems Not Addressed by 64 . . . . . . . . . . . . . . . 4
2.2. Problems Addressed by 64 . . . . . . . . . . . . . . . . . 6
2.3. Problems Addressed by NAT44 Translation Documents . . . . 7
3. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
The current 64 proposal is widely seen as the next step in the
evolution of interconnection equipment enabling communication between
IPv6-only and IPv4-only networks. One of the building blocks of this
proposal is decoupling the DNS functionality from the NAT protocol
translation itself.
This approach is pragmatic in the sense that there is no dependency
on DNS implementation for the successful functionality of NAT. As
long as there is a function (possibly DNS64) that can construct an
IPv6 address with a fixed prefix and IPv4 address as the suffix,
NAT64 will work just fine.
To understand the 64 proposal, we must keep in mind that the focus of
this proposal is on the deployment and not the implementation
details. As long as a NAT64 box confirms to the externally
behaviour, as desired in the deployment scenario, the details are not
very important as mentioned in this excerpt from
[I-D.ietf-behave-v6v4-xlate-stateful] "..... A NAT64 MAY perform the
steps in a different order, or MAY perform different steps, as long
as the externally visible outcome in the same."
1.1. Scope
This document provides an analysis of how the proposed set of
documents that specify stateful IPv6-only to IPv4-only translation
and replace NAT-PT [RFC2766] address the issues raised in the
document "Reasons to Move the Network Address Translator - Protocol
Translator (NAT-PT) to Historic Status" [RFC4966]. These documents,
henceforth referred as 64, comprise of the following:
o NAT64: Network Address and Protocol Translation from IPv6 Clients
to IPv4 Servers [I-D.ietf-behave-v6v4-xlate-stateful]
o DNS64: DNS extensions for Network Address Translation from IPv6
Clients to IPv4 Servers [I-D.ietf-behave-dns64]
o IPv6 Addressing of IPv4/IPv6 TranslatorsFramework for IPv4/IPv6
Translation [I-D.ietf-behave-address-format]
o Framework for IPv4/IPv6 Translation
[I-D.ietf-behave-v6v4-framework]
This 64 proposal analyzed is limited in the sense that hosts from
IPv6 network can initiate a connection to IPv4 network, but not vice-
versa. This corresponds to Scenarios 1 and 5 described in
[I-D.ietf-behave-v6v4-framework]. Hence, the scenario of servers
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moving to IPv6 while clients remaining IPv4 remains unaddressed.
The 64 proposal, just like any other technology under development,
has some positives and some drawbacks. The ups and downs of the
proposal must be clearly understood while going forward with its
future development.
The scope of this document does not include stateless translation.
Open Issue: should we include stateless translation in the scope?
2. Analysis of 64 Translation Against Concerns of RFC4966
Of the set of problems pointed out in RFC4966, the 64 proposal
addresses some problems, whereas leaves others unaddressed. It is
also worth pointing out that the scope of the 64 proposal is reduced
when compared to NAT-PT. Following is a point by point analysis of
the problems.
2.1. Problems Not Addressed by 64
Problems discussed in RFC4966, which are not addressed by the 64
proposal:
1. Disruption of all protocols that embed IP addresses (and/or
ports) in packet payloads or apply integrity mechanisms using IP
addresses (and ports).
Analysis: In the case of FTP [RFC0959] this problem is
addressed by the use of a FTP64 ALG [I-D.ietf-behave-ftp64]
which is a workaround solution. The functioning of other
protocols is left unaddressed.
2. Inability to redirect traffic for protocols that lack
demultiplexing capabilities or are not built on top of specific
transport-layer protocols for transport address translations.
3. Loss of information due to incompatible semantics between IPv4
and IPv6 versions of headers and protocols.
Analysis: This issue is not specific to 64 but due to the
design of IPv4 and IPv6.
4. Need for additional state and/or packet reconstruction in
dealing with packet fragmentation. Otherwise, implement no
support for fragments.
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5. Interaction with SCTP and multihoming.
Analysis: There are two issues identified under section 2.6
of [RFC4966]. The first one states that in order to support
multihoming SCTP carries embedded addresses that would have
to be translated. This is another instance of the problem
discussed earlier where NAT disrupts protocols that embeds IP
address (and/or ports) in packet payload .
The second one is that since all connections of a SCTP
multihoming session need to go through the same NAT device,
it nullifies the multihoming advantages of SCTP. This is
still true for 64.
6. Need for the NAT box to act as proxy for correspondent node when
IPv6 node is mobile, with consequent restrictions on mobility.
Analysis: This is not specific to NAT64 but to all NAT
flavours.
7. Inability to handle multicast traffic.
Analysis: efforts are underway to support translation of
multicast traffic [I-D.venaas-behave-v4v6mc-framework].
8. Scalability concerns together with introduction of a single
point of failure and a security attack nexus.
Analysis: If deployed in a centralised scheme, there is still
a single point of failure for the NAT connections. This
robustness issue may be mitigated by deploying distributed
NAT64 devices or any state synchronisation procedure.
9. Creation of a DoS (Denial of Service) threat relating to
exhaustion of memory and address/port pool resources on the
translator.
Analysis: This specific DoS concern on Page 6 of [RFC4966] is
under a DNS-ALG heading in that document, and refers to NAT-
PT's creation of NAT mapping state when a DNS query occurred.
With the new IPv6/IPv4 translation mechanisms, DNS queries do
not create mapping state. Thus, this concern is fully
eliminated with the new IPv6/IPv4 translation mechanisms.
it is important to note that a similar issue may be
encountered in 64 since static mappings may be configured on
the NAT64 devices (in addition to the dynamic per-flow state)
owing to NAT port forwarding (e.g., UPnP IGD, NAT-PMP).
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10. Restricted validity of translated DNS records: a translated
record may be forwarded to an application that cannot use it.
Analysis: If a node on the IPv4 side forwards the address of
the other endpoint to a node which cannot contact the NAT box
or is not covered under the endpoint-dependent contraint of
NAT, then the new node will not be able to initiate contact.
11. Unless UDP encapsulation is used for IPsec [RFC3498], traffic
using IPsec AH (Authentication Header), in transport and tunnel
mode, and IPsec ESP (Encapsulating Security Payload), in
transport mode, is unable to be carried through NAT-PT without
terminating the security associations on the NAT-PT, due to
their usage of cryptographic integrity protection.
Analysis: This is still true for 64.
12. Address selection issues when either the internal or external
hosts implement both IPv4 and IPv6
Analysis: This is out of scope of 64 since Scenarios 1 and 5
of [I-D.ietf-behave-v6v4-framework] assume IPv6-only hosts.
Thereofre this issue is not resolved and mitigation
techniques outside the 64 protocols need to be used. These
techniques may allow to offload NAT64 resources and prefer
native communications which do not involve translators.
Avoiding NAT devices in the path is encouraged for mobile
nodes for instance to save power consumption due to always-on
traffic and maintaining NAT states. An in-depth discussion
can be found in DNS64 Resolvers and Dual-Stack Hosts
[I-D.wing-behave-dns64-config]
2.2. Problems Addressed by 64
Problems, identified in RFC4966, which are adequately addressed by
the 64 proposal::
1. Constraints on network topology (as it relates to DNS-ALG; see
Section 3.1 of [RFC4966])
Analysis: This issue has mitigated severity as the DNS is
separate from the NAT device. Nevertheless, a minimal
coordination may be required to ensure that the NAT64 to be
crossed (the one to which the IPv4 Converted IPv6 address
returned to a requesting host) must be in the path and has
also sufficient resources to handle received traffic.
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2. Inappropriate translation of responses to A queries from IPv6
nodes.
Analysis: DNS64 does not translate A queries since the 64
documents assume IPv6-only hosts, therefore due to reduced
scope this concern has been resolved.
3. Address selection issues and resource consumption in a DNS-ALG
with multi-addressed nodes
Analysis: Since the DNS-ALG is not there and new connection
initiation is not supported from IPv4 side, their is no need
to maintain temporary states in anticipation of connections.
4. Limitations on DNS security capabilities when using a DNS-ALG.
Analysis: A DNSSEC validating stub resolver behind a DNS64 in
server mode is not supported. Therefore if a host wants to do
its own DNSSEC validation, and it wants to use a NAT64, the
host has to also perform its own DNS64 synthesis.
5. Creation of a DoS (Denial of Service) threat relating to
exhaustion of memory and address/port pool resources on the
translator.
Analysis: This specific DoS concern on Page 6 of [RFC4966] is
under a DNS-ALG heading in that document, and refers to NAT-
PT's creation of NAT mapping state when a DNS query occurred.
With the new IPv6/IPv4 translation mechanisms, DNS queries do
not create mapping state. Thus, this concern is fully
eliminated with the new IPv6/IPv4 translation mechanisms.
2.3. Problems Addressed by NAT44 Translation Documents
Some issues mentioned in RFC4966 were solved by RFC 4787 [RFC4787],
RFC 5382 [RFC5382] and RFC 5508 [RFC5508]. At the time when NAT-PT
was published these recommendations were not in place but they are
orthogonal to the translation algorithm per se, therefore they could
be implemented with NAT-PT. On the other hand, NAT64 explicitly
mentions that these recommendations need to be followed and thus
should be seen as a complete specification.
1. Requirement for applications to use keepalive mechanisms to
workaround connectivity issues caused by premature timeout for
session table and BIB entries.
Analysis: Since NAT64 follows some of the RFC4787, RFC5382 and
RFC5508 requirements, there is a high lower bound for the
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lifetime of sessions. In NAT-PT this was unknown and
applications needed to assume the worst case. For instance,
in NAT64, the lifetime for a TCP session is approximately 2
hours, so not much keep-alive signalling overhead is needed.
2. Lack of address mapping persistence: Some applications require
address retention between sessions. The user traffic will be
disrupted if a different mapping is used. The use of the DNS-
ALG to create address mappings with limited lifetimes means that
applications must start using the address shortly after the
mapping is created, as well as keep it alive once they start
using it.
Analysis: It is not clear if address persistence should be
maintained only between sessions that overlap across time.
Moreover, it is not clear if addresses persistence should be
maintained between static and dynamic bindings.
In the simpler case of address persistence between dynamic
sessions that overlap in time, since NAT64 recommends the use
of endpoint independent mapping, depending on how many other
sessions established for the same endpoint, it may be the case
that in many situations this is solved. Having said that, the
same network and port allocation scheme could be used in
NAT-PT which would make it a non-issue.
3. Conclusions
The above analysis of the solutions provided by the 64 proposal shows
that the majority of the problems that are not directly related to
the decoupling of NAT and DNS remain unaddressed.
This points to several shortcomings of 64 proposal which must be
addressed if the future network deployments have to move reliably
towards 64 as a solution to IPv6 - IPv4 interconnection.
Some of the issues, as pointed out in RFC 4966, have possible
solutions. However these solutions will require significant updates
to the 64 proposal, increasing its complexity.
4. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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5. Security Considerations
None
6. Acknowledgements
Marcelo Bagnulo and Mohamed Boucadair for their comments.
7. References
7.1. Normative References
[RFC0959] Postel, J. and J. Reynolds, "File Transfer Protocol",
STD 9, RFC 959, October 1985.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2766] Tsirtsis, G. and P. Srisuresh, "Network Address
Translation - Protocol Translation (NAT-PT)", RFC 2766,
February 2000.
[RFC4787] Audet, F. and C. Jennings, "Network Address Translation
(NAT) Behavioral Requirements for Unicast UDP", BCP 127,
RFC 4787, January 2007.
[RFC4966] Aoun, C. and E. Davies, "Reasons to Move the Network
Address Translator - Protocol Translator (NAT-PT) to
Historic Status", RFC 4966, July 2007.
[RFC5382] Guha, S., Biswas, K., Ford, B., Sivakumar, S., and P.
Srisuresh, "NAT Behavioral Requirements for TCP", BCP 142,
RFC 5382, October 2008.
[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
7.2. Informative References
[I-D.ietf-behave-address-format]
Huitema, C., Bao, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators",
draft-ietf-behave-address-format-04 (work in progress),
January 2010.
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[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-dns64-06 (work in progress),
February 2010.
[I-D.ietf-behave-ftp64]
Beijnum, I., "IPv6-to-IPv4 translation FTP
considerations", draft-ietf-behave-ftp64-00 (work in
progress), December 2009.
[I-D.ietf-behave-v6v4-framework]
Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation",
draft-ietf-behave-v6v4-framework-06 (work in progress),
February 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-08 (work in
progress), January 2010.
[I-D.venaas-behave-v4v6mc-framework]
Venaas, S., Li, X., and C. Bao, "Framework for IPv4/IPv6
Multicast Translation",
draft-venaas-behave-v4v6mc-framework-01 (work in
progress), October 2009.
[I-D.wing-behave-dns64-config]
Wing, D., "DNS64 Resolvers and Dual-Stack Hosts",
draft-wing-behave-dns64-config-01 (work in progress),
January 2010.
Authors' Addresses
Reinaldo Penno
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, California 94089
USA
Email: rpenno@juniper.net
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Tarun Saxena
Juniper Networks
Email: tsaxena@juniper.net
Dan Wing
Cisco Systems
170 West Tasman Drive
San Jose, California 95134
USA
Email: dwing@cisco.com
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