IPv6 Maintenance L. Colitti
Internet-Draft E. Kline
Intended status: Standards Track J. Linkova
Expires: April 4, 2019 Google
October 1, 2018
Discovering PREF64 in Router Advertisements
draft-pref64folks-6man-ra-pref64-02
Abstract
This document specifies a Router Advertisement option to communicate
NAT64 prefixes to clients.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. Why include the NAT64 prefix in Router Advertisements . . . . 3
3. Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Option format . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . . 4
6. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 7
10.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
NAT64 [RFC6146] with DNS64 [RFC6147] is a widely-deployed mechanism
to provide IPv4 access on IPv6-only networks. In order to support
functions such as local validation of DNSSEC [RFC4033] responses,
464xlat [RFC6877], and local IPv4 address synthesis [RFC8305], the
host must be aware of the NAT64 prefix in use by the network. This
document specifies a Router Advertisement [RFC4861] option to
communicate the NAT64 prefix to hosts.
1.1. 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].
1.2. Terminology
Pref64: an IPv6 prefix used for IPv6 address synthesis [RFC6146];
RA Router Advertisement, a message used by IPv6 routers to advertise
their presence together with various link and Internet parameters
([RFC4861]);
PvD-aware host A host that supports the association of network
configuration information into PvDs and the use of these PvDs. Also
named PvD-aware node in [RFC7556].
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2. Why include the NAT64 prefix in Router Advertisements
Fate sharing: NAT64 requires a routing to be configured. IPv6
routing configuration requires receiving an IPv6 Router Advertisement
[RFC4861]. Compared to currently-deployed NAT64 prefix discovery
methods such as [RFC7050], including the NAT64 prefix in the Router
Advertisement minimizes the number of packets required to configure a
host. This speeds up the process of connecting to a network that
supports NAT64/DNS64, and simplifies host implementation by removing
the possibility that the host can have an incomplete layer 3
configuration (e.g., IPv6 addresses and prefixes, but no NAT64
prefix).
Deployability: all IPv6 hosts and networks are required to support
[RFC4861]. Other options such as [RFC7225] require implementing
other protocols.
3. Semantics
For simplicity, this option only supports a NAT64 prefix length of 96
bits, as this is by the most common configuration used by hosts.
Networks using one of the other prefix lengths supported in
([RFC6052]) can use other mechanisms such as [RFC7050] or [RFC7225].
If different prefix lengths become common, another RA option can be
created to configure them.
This option may appear more than once in a Router Advertisement.
Host behaviour with regards to synthesizing IPv6 addresses from IPv4
addresses SHOULD follow the recommendations given in Section 3 of
[RFC7050], limited to the NAT64 prefixes that have non-zero lifetime.
This option specifies exactly one NAT64 prefix for all IPv4
destinations. If the network operator desires to route different
parts of the IPv4 address space to different NAT64 devices, this can
be accomplished by routing more specifics of the NAT64 prefix to
those devices. For example, if the operator would like to route
10.0.0.0/8 through NAT64 device A and the rest of the IPv4 space
through NAT64 device B, and the operator's NAT64 prefix is
2001:db8:a:b::/96, then the operator can route
2001:db8:a:b::a00:0/104 to NAT64 A and 2001:db8:a:b::/64 to NAT64 B.
In a network that provides both IPv4 and NAT64, it may be desirable
for certain IPv4 addresses not to be translated. An example might be
private address ranges that are local to the network and should not
be reached through the NAT64. This type of configuration cannot be
conveyed to hosts using this option, or through other NAT64 prefix
provisioning mechanisms such as [RFC7050] or [RFC7225]. This problem
does not apply in IPv6-only networks, because in such networks, the
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host does not have an IPv4 address and cannot reach any IPv4
destinations without the NAT64.
4. Option format
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Prefix +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NAT64 Prefix Option Format
Fields:
Type 8-bit identifier of the RDNSS option type as assigned by
IANA: TBD
Length 8-bit unsigned integer. The length of the option (including
the Type and Length fields) is in units of 8 octets. The
sender MUST set the Length to 2. A host MUST ignore the
NAT64 prefix option if the length field value is 1. If the
Length field value exceeds 2, the host MUST utilize the
first 16 octets and ignore the rest of the option.
Lifetime 16-bit unsigned integer. The maximum time in seconds over
which this NAT64 prefix MAY be used. The value of Lifetime
SHOULD by default be set to lesser of 3 x MaxRtrAdvInterval
or 65535 seconds. A value of zero means that the prefix
MUST no longer be used.
Prefix The 96-bit NAT64 prefix.
5. Handling Multiple NAT64 Prefixes
In some cases a host may receive multiple NAT64 prefixes from
different sources. Possible scenarios include (but are not limited
to):
o the host is using multiple mechanisms to discover Pref64 prefixes
(e.g. by using PCP ([RFC7225]) and/or by resolving IPv4-only fully
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qualified domain name ([RFC7050]) in addition to receiving the
Pref64 RA option);
o The pref64 option presents in a single RA more than once;
o the host receives multiple RAs with different Pref64 prefixes on
one or multiple interfaces.
When multiple Pref64 were discovered via RA Pref64 Option (the Option
presents more than once in a singe RA or multiple RAs were received),
host behaviour with regards to synthesizing IPv6 addresses from IPv4
addresses SHOULD follow the recommendations given in Section 3 of
[RFC7050], limited to the NAT64 prefixes that have non-zero
lifetime..
When different Pref64 are discovered by using multiple mechanisms,
hosts SHOULD select one source of infromation only. The RECOMMENDED
order is:
o PCP-discovered prefixes ([RFC7225]), if supported;
o Pref64 discovered via RA Option;
o Pref64 resolving IPv4-only fully qualified domain name ([RFC7050])
Note that if the network provides Pref64 both via this RA option and
[RFC7225], hosts that receive the Pref64 via RA option may choose to
use it imediately before waiting for PCP to complete, and therefore
some traffic may not reflect any more detailed configuration provided
by PCP.
6. Multihoming
Like most IPv6 configuration information, the Pref64 option is
specific to the network on which it is received. For example, a
Pref64 option received on a particular wireless network may not be
usable unless the traffic is also sourced on that network.
Similarly, a host connected to a cellular network that povides NAT64
generally cannot use that NAT64 for destinations reached through a
VPN tunnel that terminates outside that network.
Thus, correct use of this option on a multihomed host generally
requires the host to be PVD-aware.
This issue is not specific to the Pref64 RA option and, for example,
is quite typical for DNS resolving on multihomed hosts (e.g. a host
might resolve a destination name by using the corporate DNS server
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via the VPN tunnel but then send the traffic via its Internet-facing
interface).
7. IANA Considerations
The IANA is requested to assign a new IPv6 Neighbor Discovery Option
type for the PREF64 option defined in this document.
+---------------+-------+
| Option Name | Type |
+---------------+-------+
| PREF64 option | (TBD) |
+---------------+-------+
Table 1
The IANA registry for these options is:
https://www.iana.org/assignments/icmpv6-parameters [1]
8. Security Considerations
Because Router Advertisements are required in all IPv6 configuration
scenarios, on IPv6-only networks, Router Advertisements must already
be secured, e.g., by deploying RA guard [RFC6105]. Providing all
configuration in Router Advertisements increases security by ensuring
that no other protocols can be abused by malicious attackers to
provide hosts with invalid configuration.
The security measures that must already be in place to ensure that
Router Advertisements are only received from legitimate sources
eliminate the problem of NAT64 prefix validation described in section
3.1 of [RFC7050].
9. Acknowledgements
Thanks to the following people (in alphabetical order) for their
review and feedback: Brian E Carpenter, Nick Heatley, David Schinazi.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
DOI 10.17487/RFC6052, October 2010,
<https://www.rfc-editor.org/info/rfc6052>.
10.2. Informative References
[I-D.ietf-intarea-provisioning-domains]
Pfister, P., Vyncke, E., Pauly, T., Schinazi, D., and W.
Shao, "Discovering Provisioning Domain Names and Data",
draft-ietf-intarea-provisioning-domains-02 (work in
progress), June 2018.
[RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements",
RFC 4033, DOI 10.17487/RFC4033, March 2005,
<https://www.rfc-editor.org/info/rfc4033>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC6105] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J.
Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105,
DOI 10.17487/RFC6105, February 2011,
<https://www.rfc-editor.org/info/rfc6105>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[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,
DOI 10.17487/RFC6147, April 2011,
<https://www.rfc-editor.org/info/rfc6147>.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation",
RFC 6877, DOI 10.17487/RFC6877, April 2013,
<https://www.rfc-editor.org/info/rfc6877>.
[RFC7050] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis",
RFC 7050, DOI 10.17487/RFC7050, November 2013,
<https://www.rfc-editor.org/info/rfc7050>.
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[RFC7225] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the
Port Control Protocol (PCP)", RFC 7225,
DOI 10.17487/RFC7225, May 2014,
<https://www.rfc-editor.org/info/rfc7225>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/info/rfc7556>.
[RFC8305] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2:
Better Connectivity Using Concurrency", RFC 8305,
DOI 10.17487/RFC8305, December 2017,
<https://www.rfc-editor.org/info/rfc8305>.
10.3. URIs
[1] https://www.iana.org/assignments/icmpv6-parameters
Authors' Addresses
Lorenzo Colitti
Google
Roppongi 6-10-1
Minato, Tokyo 106-6126
JP
Email: lorenzo@google.com
Erik Kline
Google
Roppongi 6-10-1
Minato, Tokyo 106-6126
JP
Email: ek@google.com
Jen Linkova
Google
1 Darling Island Rd
Pyrmont, NSW 2009
AU
Email: furry@google.com
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