IPv6 Maintenance L. ColittiInternet-Draft J. LinkovaIntended status: Standards Track GoogleExpires: April 5, 2020 October 3, 2019Discovering PREF64 in Router Advertisementsdraft-ietf-6man-ra-pref64-06Abstract This document specifies a Router Advertisement option to communicate NAT64 prefixes to hosts.Status of This Memo This Internet-Draft is submitted in full conformance with the provisions ofBCP 78 andBCP 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- Drafts is athttps://datatracker.ietf.org/drafts/current/. 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 April 5, 2020.Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents 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.Colitti & Linkova Expires April 5, 2020 [Page 1]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019Table of Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .21.1. Requirements Language . . . . . . . . . . . . . . . . . .21.2. Terminology . . . . . . . . . . . . . . . . . . . . . . .22. Use cases for communicating the NAT64 prefix to hosts . . . .33. Why include the NAT64 prefix in Router Advertisements . . . .34. Usage Guidelines . . . . . . . . . . . . . . . . . . . . . .45. Option format . . . . . . . . . . . . . . . . . . . . . . . .46. Handling Multiple NAT64 Prefixes . . . . . . . . . . . . . .67. PREF64 Consistency . . . . . . . . . . . . . . . . . . . . .78. IANA Considerations . . . . . . . . . . . . . . . . . . . . .89. Security Considerations . . . . . . . . . . . . . . . . . . .810. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .811. References . . . . . . . . . . . . . . . . . . . . . . . . .811.1. Normative References . . . . . . . . . . . . . . . . . .811.2. Informative References . . . . . . . . . . . . . . . . .911.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . .10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . .101. 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 inRFC 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]; DNS64: a mechanism for synthesizing AAAA records from A records [RFC6147];Colitti & Linkova Expires April 5, 2020 [Page 2]
Internet-Draft Discovering PREF64 in Router Advertisements October 20192. 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 Enabling DNS64 functions on end hosts. In particular: * Local DNSSEC validation (DNS64 in stub-resolver mode). 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. * 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). * 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. o Enabling NAT64 address translation functions on end hosts. For example: * IPv4 address literals on an IPv6-only host. As described in[RFC8305] section 7.1, IPv6-only hosts connecting to IPv4 address literals can translate the IPv4 literal to an IPv6 literal. * 464XLAT [RFC6877]. 464XLAT requires the host be aware of the NAT64 prefix.3. Why include the NAT64 prefix in Router Advertisements Fate sharing: NAT64 requires routing to be configured. IPv6 routing configuration requires receiving an IPv6 Router Advertisement [RFC4861]. Therefore using Router Advertisements to provide hosts with NAT64 prefix ensures that NAT64 reachability information shares fate with the rest of network configuration on the host. Atomic configuration: including the NAT64 prefix in the Router Advertisement minimizes the number of packets required to configure a host. Only one packet (a Router Advertisement) is required to complete the network configuration. 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 canColitti & Linkova Expires April 5, 2020 [Page 3]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019 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. Deployability: all IPv6 hosts and networks are required to support Neighbor Discovery [RFC4861] so just a minor extension to the existing implementation is required. Other options such as [RFC7225] require implementing other protocols (e.g. PCP [RFC7225]) which could be considered an obstacle for deployment.4. Usage Guidelines 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 inSection 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..5. Option formatColitti & Linkova Expires April 5, 2020 [Page 4]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019 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 | PLC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | Highest 96 bits of the Prefix | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: NAT64 Prefix Option Format Fields:Colitti & Linkova Expires April 5, 2020 [Page 5]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019 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. The sender MUST set the length to 2. The receiver MUST ignore the PREF64 option if the length field value is not 2. Lifetime 13-bit unsigned integer. The maximum time in units of 8 seconds over which this NAT64 prefix MAY be used. The value of Lifetime SHOULD by default be set to the lesser of 3 x MaxRtrAdvInterval divided by 8, or 8191. The receiver MUST multiply the Lifetime value by 8 (for example, by logical left shift) to calculate the maximum time in seconds the prefix MAY be used. Lifetime of 0 indicates that the prefix SHOULD NOT be used anymore. Router vendors SHOULD allow administrators to specify non-zero lifetime values which are not divisible by 8. In such cases the router SHOULD round the provided value up to the lesser of nearest integer divisible by 8, or 65528 and divide the result by 8 (or just perform a logical right-shift by 3) and set the Lifetime field to the resulting value. PLC 3-bit unsigned integer. This field encodes the NAT64 Prefix (Prefix Length defined in [RFC6052]. The PLC field values 0, 1, 2, Length 3, 4 and 5 indicate the NAT64 prefix length of 96, 64, 56, Code) 48, 40 and 32 bits respectively. The receiver MUST ignore the PREF64 option if the prefix length code field is not set to one of those values. Highest 96-bit unsigned integer. Contains bits 0 - 95 of the NAT64 96 bits prefix. of the prefix6. 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 qualified domain name [RFC7050] in addition to receiving the PREF64 RA option); o the PREF64 option presents in a single RA more than once;Colitti & Linkova Expires April 5, 2020 [Page 6]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019 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 inSection 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. PREF64 ConsistencySection 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.Colitti & Linkova Expires April 5, 2020 [Page 7]
Internet-Draft Discovering PREF64 in Router Advertisements October 20198. 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]9. 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 insection3.1 of [RFC7050].10. 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, Robert Hinden, Martin Hunek, Tatuya Jinmei, Erik Kline, David Lamparter, Jordi Palet Martinez, Tommy Pauly, Alexandre Petrescu, Michael Richardson, David Schinazi, Ole Troan, Bernie Volz.11. References11.1. 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>.Colitti & Linkova Expires April 5, 2020 [Page 8]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019 [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>. [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>.11.2. Informative References [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>. [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>. [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>.Colitti & Linkova Expires April 5, 2020 [Page 9]
Internet-Draft Discovering PREF64 in Router Advertisements October 2019 [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>.11.3. URIs [1]https://www.iana.org/assignments/icmpv6-parametersAuthors' Addresses Lorenzo Colitti Google Shibuya 3-21-3 Shibuya, Tokyo 150-0002 JP Email: lorenzo@google.com Jen Linkova Google 1 Darling Island Rd Pyrmont, NSW 2009 AU Email: furry@google.comColitti & Linkova Expires April 5, 2020 [Page 10]
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draft-ietf-6man-ra-pref64-06
This is an older version of an Internet-Draft that was ultimately published asRFC 8781.
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