Discovering PREF64 in Router Advertisements
draft-ietf-6man-ra-pref64-04
The information below is for an old version of the document.
| Document | Type | Active Internet-Draft (6man WG) | |
|---|---|---|---|
| Authors | Lorenzo Colitti , Jen Linkova | ||
| Last updated | 2019-09-05 (Latest revision 2019-08-11) | ||
| Replaces | draft-pref64folks-6man-ra-pref64 | ||
| Stream | Internet Engineering Task Force (IETF) | ||
| Formats | plain text xml htmlized pdfized bibtex | ||
| Reviews | |||
| Stream | WG state | In WG Last Call | |
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draft-ietf-6man-ra-pref64-04
IPv6 Maintenance L. Colitti
Internet-Draft J. Linkova
Intended status: Standards Track Google
Expires: February 12, 2020 August 11, 2019
Discovering PREF64 in Router Advertisements
draft-ietf-6man-ra-pref64-04
Abstract
This document specifies a Router Advertisement option to communicate
NAT64 prefixes to clients.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF). Note that other groups may also distribute
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on February 12, 2020.
Copyright Notice
Copyright (c) 2019 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
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described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2. Use cases for communicating the NAT64 prefix to hosts . . . . 3
3. Why include the NAT64 prefix in Router Advertisements . . . . 3
4. Semantics . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Option format . . . . . . . . . . . . . . . . . . . . . . . . 4
6. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . . 6
7. Multihoming . . . . . . . . . . . . . . . . . . . . . . . . . 7
8. Pref64 Consistency . . . . . . . . . . . . . . . . . . . . . 8
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 9
12.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
NAT64 [RFC6146] with DNS64 [RFC6147] is a widely-deployed mechanism
to provide IPv4 access on IPv6-only networks. In various scenarios,
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 (or NAT64 prefix): an IPv6 prefix used for IPv6 address
synthesis [RFC6146];
NAT64: Network Address and Protocol Translation from IPv6 Clients to
IPv4 Servers ([RFC6146]);
RA: Router Advertisement, a message used by IPv6 routers to advertise
their presence together with various link and Internet parameters
([RFC4861]);
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DNS64: a mechanism for synthesizing AAAA records from A records
([RFC6147]);
2. Use cases for communicating the NAT64 prefix to hosts
On networks employing NAT64, it is useful for hosts to know the NAT64
prefix for several reasons, including the following:
o Local DNSSEC validation. As discussed in [RFC6147] section 2, the
stub resolver in the host "will try to obtain (real) AAAA RRs, and
in case they are not available, the DNS64 function will synthesize
AAAA RRs for internal usage." This is required in order to use
DNSSEC on a NAT64 network.
o IPv4 address literals on an IPv6-only host. As described in
[RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 address
literals can resolve the IPv4 literal to an IPv6 address.
o 464XLAT [RFC6877]. 464XLAT is widely deployed and requires that
the host be aware of the NAT64 prefix.
o Trusted DNS server. AAAA synthesis is required for the host to be
able to use a DNS server not provided by the network (e.g., a DNS-
over-TLS server ([RFC7858]) with which the host has an existing
trust relationship).
o Networks with no DNS64 server. Hosts that support AAAA synthesis
and that are aware of the NAT64 prefix in use do not need the
network to perform the DNS64 function at all.
3. 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).
Updatability: it is possible to change the NAT64 prefix at any time,
because when it changes, it is possible to notify hosts by sending a
new Router Advertisement.
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Deployability: all IPv6 hosts and networks are required to support
[RFC4861]. Other options such as [RFC7225] require implementing
other protocols.
4. Semantics
To support prefix lengths defined in ([RFC6052]) this option contains
the prefix length field. However as /96 prefix is considered to be
the most common use case, the prefix length field is optional and
only presents for non-/96 prefixes. It allows to keep the option
length to a minimum (16 bytes) for the most common case and increase
it to 20 bytes for non-/96 prefixes only (see Section 5 below for
more details).
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.
This option may appear more than once in a Router Advertisement (e.g.
in case of graceful renumbering the network from one NAT64 prefix to
another). 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.
In a network (or a provisioning domain) 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/provisioning domain 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 host does
not have an IPv4 address and cannot reach any IPv4 destinations
without the NAT64. The multihoming and multiple provisioning domains
scenarios are discussed in Section 7.
5. Option format
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| Highest 96 bits of the Prefix |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lowest bits (96-127) of the prefix (optional, if Length > 2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NAT64 Prefix Option Format
Fields:
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Type 8-bit identifier of the Pref64 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. If the
prefix length is 96 bits the sender MUST set the Length to 2
and include the 96 bits of the prefix in the option. If the
prefix length is not 96 bits then the sender MUST set the
length to 3 and include all 128 bits of the prefix in the
Prefix field and set the Prefix Length field to the prefix
length. The receiver MUST ignore the Pref64 option if the
length field value is 1. If the Length field value exceeds
3, the receiver MUST utilize the first 21 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.
Highest 96-bit unsigned integer. Contains bits 0 - 95 of the NAT64
96 bits prefix.
of the
prefix
Lowest 32-bit unsigned integer. Contains bits 96 - 127 of the NAT64
bits of prefix. This field is optional and presents only if the
the prefix length is not 96 bits.
prefix
Prefix 8-bit unsigned integer. Optional field which present only if
Length the prefix length is not 96 bits. The sender MUST set it
only to one of the following values: 32, 40, 48, 56, 64
([RFC6052]. The receiver MUST ignore the Pref64 option if
the prefix length value is not set to one of those numbers.
Reserved A 3-byte unused field. If present it MUST be initialized to
zero by the sender and MUST be ignored by the receiver. This
field is optional and presents only if the prefix length is
not 96 bits.
6. 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):
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o the host is using multiple mechanisms to discover Pref64 prefixes
(e.g. by using PCP ([RFC7225]) and/or by resolving IPv4-only fully
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 single 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 information 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 immediately before waiting for PCP to complete, and therefore
some traffic may not reflect any more detailed configuration provided
by PCP.
7. 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 provides 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 support the concept of multiple Provisioning
Domains (PvD, a set of configuration information associated with a
network, [RFC7556]) and to be able to use these PvDs.
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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
via the VPN tunnel but then send the traffic via its Internet-facing
interface).
8. Pref64 Consistency
Section 6.2.7 of [RFC4861] recommends that routers inspect RAs sent
by other routers to ensure that all routers onlink advertise the
consistent information. Routers SHOULD inspect valid Pref64 options
received on a given link and verify the consistency. Detected
inconsistencies indicate that one or more routers might be
misconfigured. Routers SHOULD log such cases to system or network
management. Routers SHOULD check and compare the following
information:
o set of Pref64 with non-zero lifetime;
o set of Pref64 with zero lifetime.
PvD-aware routers MUST only compare information scoped to the same
implicit or explicit PvD.
9. 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]
10. 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
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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].
11. Acknowledgements
Thanks to the following people (in alphabetical order) for their
review and feedback: Mikael Abrahamsson, Mark Andrews, Brian E
Carpenter, David Farmer, Nick Heatley, Martin Hunek, Tatuya Jinmei,
Erik Kline, David Lamparter, Jordi Palet Martinez, Tommy Pauly,
Michael Richardson, David Schinazi.
12. References
12.1. 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>.
[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>.
[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>.
12.2. 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-05 (work in
progress), June 2019.
[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>.
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[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>.
[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>.
[RFC7858] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D.,
and P. Hoffman, "Specification for DNS over Transport
Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May
2016, <https://www.rfc-editor.org/info/rfc7858>.
[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>.
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12.3. 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
Jen Linkova
Google
1 Darling Island Rd
Pyrmont, NSW 2009
AU
Email: furry@google.com
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