Difference between revisions of "RFC8781"
| Line 23: | Line 23: | ||
received public review and has been approved for publication by the | received public review and has been approved for publication by the | ||
Internet Engineering Steering Group (IESG). Further information on | Internet Engineering Steering Group (IESG). Further information on | ||
| − | Internet Standards is available in Section 2 of | + | Internet Standards is available in Section 2 of RFC 7841. |
Information about the current status of this document, any errata, | Information about the current status of this document, any errata, | ||
| Line 34: | Line 34: | ||
document authors. All rights reserved. | document authors. All rights reserved. | ||
| − | This document is subject to | + | This document is subject to BCP 78 and the IETF Trust's Legal |
Provisions Relating to IETF Documents | Provisions Relating to IETF Documents | ||
(https://trustee.ietf.org/license-info) in effect on the date of | (https://trustee.ietf.org/license-info) in effect on the date of | ||
| Line 64: | Line 64: | ||
== Introduction == | == Introduction == | ||
| − | NAT64 [[RFC6146]] with DNS Extensions for Network Address Translation | + | NAT64 [[[RFC6146]]] with DNS Extensions for Network Address Translation |
| − | from IPv6 clients to IPv4 servers (DNS64) [[RFC6147]] is a widely | + | from IPv6 clients to IPv4 servers (DNS64) [[[RFC6147]]] is a widely |
deployed mechanism to provide IPv4 access on IPv6-only networks. In | deployed mechanism to provide IPv4 access on IPv6-only networks. In | ||
various scenarios, the host must be aware of the NAT64 prefix in use | various scenarios, the host must be aware of the NAT64 prefix in use | ||
by the network. This document specifies a Neighbor Discovery | by the network. This document specifies a Neighbor Discovery | ||
| − | [[RFC4861]] option to be used in Router Advertisements (RAs) to | + | [[[RFC4861]]] option to be used in Router Advertisements (RAs) to |
communicate NAT64 prefixes to hosts. | communicate NAT64 prefixes to hosts. | ||
| Line 77: | Line 77: | ||
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and | "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and | ||
"OPTIONAL" in this document are to be interpreted as described in | "OPTIONAL" in this document are to be interpreted as described in | ||
| − | + | BCP 14 [[[RFC2119]]] [[[RFC8174]]] when, and only when, they appear in all | |
capitals, as shown here. | capitals, as shown here. | ||
| Line 83: | Line 83: | ||
PREF64 (or NAT64 prefix): An IPv6 prefix used for IPv6 address | PREF64 (or NAT64 prefix): An IPv6 prefix used for IPv6 address | ||
| − | synthesis [[RFC6146]]; | + | synthesis [[[RFC6146]]]; |
NAT64: Network Address and Protocol Translation from IPv6 clients to | NAT64: Network Address and Protocol Translation from IPv6 clients to | ||
| − | IPv4 servers [[RFC6146]]; | + | IPv4 servers [[[RFC6146]]]; |
Router Advertisement (RA): A message used by IPv6 routers to | Router Advertisement (RA): A message used by IPv6 routers to | ||
advertise their presence together with various link and Internet | advertise their presence together with various link and Internet | ||
| − | parameters [[RFC4861]]; | + | parameters [[[RFC4861]]]; |
DNS64: a mechanism for synthesizing AAAA records from A records | DNS64: a mechanism for synthesizing AAAA records from A records | ||
| − | [[RFC6147]]; | + | [[[RFC6147]]]; |
== Use Cases for Communicating the NAT64 Prefix to Hosts == | == Use Cases for Communicating the NAT64 Prefix to Hosts == | ||
| Line 103: | Line 103: | ||
- Local DNSSEC validation (DNS64 in stub-resolver mode). As | - Local DNSSEC validation (DNS64 in stub-resolver mode). As | ||
| − | discussed in [[RFC6147]], Section 2, the stub resolver in the | + | discussed in [[[RFC6147]]], Section 2, the stub resolver in the |
host "will try to obtain (real) AAAA RRs, and in case they are | host "will try to obtain (real) AAAA RRs, and in case they are | ||
not available, the DNS64 function will synthesize AAAA RRs for | not available, the DNS64 function will synthesize AAAA RRs for | ||
| Line 112: | Line 112: | ||
- Trusted DNS server. AAAA synthesis is required for the host to | - 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., | be able to use a DNS server not provided by the network (e.g., | ||
| − | a DNS-over-TLS [[RFC7858]] or DNS-over-HTTPS [[RFC8484]] server | + | a DNS-over-TLS [[[RFC7858]]] or DNS-over-HTTPS [[[RFC8484]]] server |
with which the host has an existing trust relationship). | with which the host has an existing trust relationship). | ||
| Line 123: | Line 123: | ||
- IPv4 address literals on an IPv6-only host. As described in | - IPv4 address literals on an IPv6-only host. As described in | ||
| − | [[RFC8305]], Section 7.1, IPv6-only hosts connecting to IPv4 | + | [[[RFC8305]]], Section 7.1, IPv6-only hosts connecting to IPv4 |
address literals can translate the IPv4 literal to an IPv6 | address literals can translate the IPv4 literal to an IPv6 | ||
literal. | literal. | ||
| − | - 464XLAT [[RFC6877]]. 464XLAT requires the host be aware of the | + | - 464XLAT [[[RFC6877]]]. 464XLAT requires the host be aware of the |
NAT64 prefix. | NAT64 prefix. | ||
| Line 133: | Line 133: | ||
Fate sharing: NAT64 requires routing to be configured. IPv6 routing | Fate sharing: NAT64 requires routing to be configured. IPv6 routing | ||
| − | configuration requires receiving an IPv6 RA [[RFC4861]]. Therefore, | + | configuration requires receiving an IPv6 RA [[[RFC4861]]]. Therefore, |
using RAs to provide hosts with the NAT64 prefix ensures that | using RAs to provide hosts with the NAT64 prefix ensures that | ||
NAT64 reachability information shares the fate of the rest of the | NAT64 reachability information shares the fate of the rest of the | ||
| Line 152: | Line 152: | ||
Deployability: All IPv6 hosts and networks are required to support | Deployability: All IPv6 hosts and networks are required to support | ||
| − | Neighbor Discovery [[RFC4861]] so just a minor extension to the | + | Neighbor Discovery [[[RFC4861]]] so just a minor extension to the |
existing implementation is required. Other options, such as | existing implementation is required. Other options, such as | ||
| − | [[RFC7225]], require implementing other protocols (e.g., Port | + | [[[RFC7225]]], require implementing other protocols (e.g., Port |
| − | Control Protocol (PCP) [[RFC7225]]), which could be considered an | + | Control Protocol (PCP) [[[RFC7225]]]), which could be considered an |
obstacle for deployment. | obstacle for deployment. | ||
| Line 188: | Line 188: | ||
PLC (Prefix Length Code): 3-bit unsigned integer. This field | PLC (Prefix Length Code): 3-bit unsigned integer. This field | ||
| − | encodes the NAT64 Prefix Length defined in [[RFC6052]]. The PLC | + | encodes the NAT64 Prefix Length defined in [[[RFC6052]]]. The PLC |
field values 0, 1, 2, 3, 4, and 5 indicate the NAT64 prefix length | field values 0, 1, 2, 3, 4, and 5 indicate the NAT64 prefix length | ||
of 96, 64, 56, 48, 40, and 32 bits, respectively. The receiver | of 96, 64, 56, 48, 40, and 32 bits, respectively. The receiver | ||
| Line 201: | Line 201: | ||
It would be highly undesirable for the NAT64 prefix to have a | It would be highly undesirable for the NAT64 prefix to have a | ||
lifetime shorter than the Router Lifetime, which is defined in | lifetime shorter than the Router Lifetime, which is defined in | ||
| − | Section 4.2 of [[RFC4861]] as a 16-bit unsigned integer. If the NAT64 | + | Section 4.2 of [[[RFC4861]]] as a 16-bit unsigned integer. If the NAT64 |
prefix lifetime is not at least equal to the default Router Lifetime, | prefix lifetime is not at least equal to the default Router Lifetime, | ||
it might lead to scenarios in which the NAT64 prefix lifetime expires | it might lead to scenarios in which the NAT64 prefix lifetime expires | ||
| Line 216: | Line 216: | ||
By default, the value of the Scaled Lifetime field SHOULD be set to | By default, the value of the Scaled Lifetime field SHOULD be set to | ||
| − | the lesser of 3 x MaxRtrAdvInterval [[RFC4861]] divided by 8, or 8191. | + | the lesser of 3 x MaxRtrAdvInterval [[[RFC4861]]] divided by 8, or 8191. |
Router vendors SHOULD allow administrators to specify nonzero | Router vendors SHOULD allow administrators to specify nonzero | ||
| Line 236: | Line 236: | ||
accomplished by routing more specific subprefixes of the NAT64 prefix | accomplished by routing more specific subprefixes of the NAT64 prefix | ||
to those devices. For example, suppose an operator is using the | to those devices. For example, suppose an operator is using the | ||
| − | [[RFC1918]] address space 10.0.0.0/8 internally. That operator might | + | [[[RFC1918]]] address space 10.0.0.0/8 internally. That operator might |
want to route 10.0.0.0/8 through NAT64 device A, and the rest of the | want to route 10.0.0.0/8 through NAT64 device A, and the rest of the | ||
IPv4 space through NAT64 device B. If the operator's NAT64 prefix is | IPv4 space through NAT64 device B. If the operator's NAT64 prefix is | ||
| Line 246: | Line 246: | ||
behavior with regard to synthesizing IPv6 addresses from IPv4 | behavior with regard to synthesizing IPv6 addresses from IPv4 | ||
addresses SHOULD follow the recommendations given in Section 3 of | addresses SHOULD follow the recommendations given in Section 3 of | ||
| − | [[RFC7050]], limited to the NAT64 prefixes that have a nonzero | + | [[[RFC7050]]], limited to the NAT64 prefixes that have a nonzero |
lifetime. | lifetime. | ||
| Line 255: | Line 255: | ||
reached through the NAT64. This type of configuration cannot be | reached through the NAT64. This type of configuration cannot be | ||
conveyed to hosts using this option, or through other NAT64 prefix | conveyed to hosts using this option, or through other NAT64 prefix | ||
| − | provisioning mechanisms such as [[RFC7050]] or [[RFC7225]]. This problem | + | provisioning mechanisms such as [[[RFC7050]]] or [[[RFC7225]]]. This problem |
does not apply in IPv6-only networks: the host in an IPv6-only | does not apply in IPv6-only networks: the host in an IPv6-only | ||
network does not have an IPv4 address and cannot reach any IPv4 | network does not have an IPv4 address and cannot reach any IPv4 | ||
| Line 267: | Line 267: | ||
* the host is using multiple mechanisms to discover PREF64 prefixes | * the host is using multiple mechanisms to discover PREF64 prefixes | ||
| − | (e.g., by using PCP [[RFC7225]]) and/or resolving an IPv4-only fully | + | (e.g., by using PCP [[[RFC7225]]]) and/or resolving an IPv4-only fully |
| − | qualified domain name [[RFC7050]] in addition to receiving the | + | qualified domain name [[[RFC7050]]] in addition to receiving the |
PREF64 RA option); | PREF64 RA option); | ||
| Line 280: | Line 280: | ||
received), host behavior with regard to synthesizing IPv6 addresses | received), host behavior with regard to synthesizing IPv6 addresses | ||
from IPv4 addresses SHOULD follow the recommendations given in | from IPv4 addresses SHOULD follow the recommendations given in | ||
| − | Section 3 of [[RFC7050]], limited to the NAT64 prefixes that have a | + | Section 3 of [[[RFC7050]]], limited to the NAT64 prefixes that have a |
nonzero lifetime. | nonzero lifetime. | ||
| Line 287: | Line 287: | ||
order is: | order is: | ||
| − | * PCP-discovered prefixes [[RFC7225]], if supported; | + | * PCP-discovered prefixes [[[RFC7225]]], if supported; |
* PREF64s discovered via the RA Option; | * PREF64s discovered via the RA Option; | ||
* PREF64s resolving an IPv4-only fully qualified domain name | * PREF64s resolving an IPv4-only fully qualified domain name | ||
| − | [[RFC7050]] | + | [[[RFC7050]]] |
Note: If the network provides PREF64s via both this RA Option and | Note: If the network provides PREF64s via both this RA Option and | ||
| − | [[RFC7225]], hosts that receive the PREF64 via the RA Option may choose | + | [[[RFC7225]]], hosts that receive the PREF64 via the RA Option may choose |
to use it immediately (before waiting for the PCP to complete); | to use it immediately (before waiting for the PCP to complete); | ||
therefore, some traffic may not reflect any more detailed | therefore, some traffic may not reflect any more detailed | ||
| Line 302: | Line 302: | ||
The host SHOULD treat the PREF64 as being specific to the network | The host SHOULD treat the PREF64 as being specific to the network | ||
interface it was received on. Hosts that are aware of Provisioning | interface it was received on. Hosts that are aware of Provisioning | ||
| − | Domain (PvD, [[RFC7556]]) MUST treat the PREF64 as being scoped to the | + | Domain (PvD, [[[RFC7556]]]) MUST treat the PREF64 as being scoped to the |
implicit or explicit PvD. | implicit or explicit PvD. | ||
=== PREF64 Consistency === | === PREF64 Consistency === | ||
| − | Section 6.2.7 of [[RFC4861]] recommends that routers inspect RAs sent | + | Section 6.2.7 of [[[RFC4861]]] recommends that routers inspect RAs sent |
by other routers to ensure that all routers onlink advertise | by other routers to ensure that all routers onlink advertise | ||
consistent information. Routers SHOULD inspect valid PREF64 options | consistent information. Routers SHOULD inspect valid PREF64 options | ||
| Line 320: | Line 320: | ||
* set of PREF64s with a zero lifetime. | * set of PREF64s with a zero lifetime. | ||
| − | Routers that are aware of PvD ([[RFC7556]]) MUST only compare | + | Routers that are aware of PvD ([[[RFC7556]]]) MUST only compare |
information scoped to the same implicit or explicit PvD. | information scoped to the same implicit or explicit PvD. | ||
| Line 342: | Line 342: | ||
Because RAs are required in all IPv6 configuration scenarios, on | Because RAs are required in all IPv6 configuration scenarios, on | ||
IPv6-only networks, RAs must already be secured -- e.g., by deploying | IPv6-only networks, RAs must already be secured -- e.g., by deploying | ||
| − | an RA-Guard [[RFC6105]]. Providing all configuration in RAs reduces | + | an RA-Guard [[[RFC6105]]]. Providing all configuration in RAs reduces |
the attack surface to be targeted by malicious attackers trying to | the attack surface to be targeted by malicious attackers trying to | ||
provide hosts with invalid configuration, as compared to distributing | provide hosts with invalid configuration, as compared to distributing | ||
| Line 354: | Line 354: | ||
if attackers are capable of sending rogue RAs, they can perform | if attackers are capable of sending rogue RAs, they can perform | ||
denial-of-service or man-in-the-middle attacks, as described in | denial-of-service or man-in-the-middle attacks, as described in | ||
| − | [[RFC6104]]. | + | [[[RFC6104]]]. |
The security measures that must already be in place to ensure that | The security measures that must already be in place to ensure that | ||
RAs are only received from legitimate sources eliminate the problem | RAs are only received from legitimate sources eliminate the problem | ||
| − | of NAT64 prefix validation described in Section 3.1 of [[RFC7050]]. | + | of NAT64 prefix validation described in Section 3.1 of [[[RFC7050]]]. |
== References == | == References == | ||
| Line 368: | Line 368: | ||
<https://www.iana.org/assignments/icmpv6-parameters>. | <https://www.iana.org/assignments/icmpv6-parameters>. | ||
| − | [[RFC2119]] Bradner, S., "Key words for use in RFCs to Indicate | + | [[[RFC2119]]] Bradner, S., "Key words for use in RFCs to Indicate |
| − | Requirement Levels", | + | Requirement Levels", BCP 14, RFC 2119, |
DOI 10.17487/RFC2119, March 1997, | DOI 10.17487/RFC2119, March 1997, | ||
<https://www.rfc-editor.org/info/rfc2119>. | <https://www.rfc-editor.org/info/rfc2119>. | ||
| − | [[RFC4861]] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, | + | [[[RFC4861]]] Narten, T., Nordmark, E., Simpson, W., and H. Soliman, |
| − | "Neighbor Discovery for IP version 6 (IPv6)", | + | "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861, |
DOI 10.17487/RFC4861, September 2007, | DOI 10.17487/RFC4861, September 2007, | ||
<https://www.rfc-editor.org/info/rfc4861>. | <https://www.rfc-editor.org/info/rfc4861>. | ||
| − | [[RFC6052]] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. | + | [[[RFC6052]]] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X. |
| − | Li, "IPv6 Addressing of IPv4/IPv6 Translators", | + | Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052, |
DOI 10.17487/RFC6052, October 2010, | DOI 10.17487/RFC6052, October 2010, | ||
<https://www.rfc-editor.org/info/rfc6052>. | <https://www.rfc-editor.org/info/rfc6052>. | ||
| − | [[RFC7050]] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of | + | [[[RFC7050]]] Savolainen, T., Korhonen, J., and D. Wing, "Discovery of |
the IPv6 Prefix Used for IPv6 Address Synthesis", | the IPv6 Prefix Used for IPv6 Address Synthesis", | ||
| − | + | RFC 7050, DOI 10.17487/RFC7050, November 2013, | |
<https://www.rfc-editor.org/info/rfc7050>. | <https://www.rfc-editor.org/info/rfc7050>. | ||
| − | [[RFC8174]] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC | + | [[[RFC8174]]] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC |
| − | 2119 Key Words", | + | 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, |
May 2017, <https://www.rfc-editor.org/info/rfc8174>. | May 2017, <https://www.rfc-editor.org/info/rfc8174>. | ||
=== Informative References === | === Informative References === | ||
| − | [[RFC1918]] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. | + | [[[RFC1918]]] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G. |
J., and E. Lear, "Address Allocation for Private | J., and E. Lear, "Address Allocation for Private | ||
| − | Internets", | + | Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918, |
February 1996, <https://www.rfc-editor.org/info/rfc1918>. | February 1996, <https://www.rfc-editor.org/info/rfc1918>. | ||
| − | [[RFC6104]] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement | + | [[[RFC6104]]] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement |
| − | Problem Statement", | + | Problem Statement", RFC 6104, DOI 10.17487/RFC6104, |
February 2011, <https://www.rfc-editor.org/info/rfc6104>. | February 2011, <https://www.rfc-editor.org/info/rfc6104>. | ||
| − | [[RFC6105]] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. | + | [[[RFC6105]]] Levy-Abegnoli, E., Van de Velde, G., Popoviciu, C., and J. |
| − | Mohacsi, "IPv6 Router Advertisement Guard", | + | Mohacsi, "IPv6 Router Advertisement Guard", RFC 6105, |
DOI 10.17487/RFC6105, February 2011, | DOI 10.17487/RFC6105, February 2011, | ||
<https://www.rfc-editor.org/info/rfc6105>. | <https://www.rfc-editor.org/info/rfc6105>. | ||
| − | [[RFC6146]] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful | + | [[[RFC6146]]] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful |
NAT64: Network Address and Protocol Translation from IPv6 | NAT64: Network Address and Protocol Translation from IPv6 | ||
| − | Clients to IPv4 Servers", | + | Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146, |
April 2011, <https://www.rfc-editor.org/info/rfc6146>. | April 2011, <https://www.rfc-editor.org/info/rfc6146>. | ||
| − | [[RFC6147]] Bagnulo, M., Sullivan, A., Matthews, P., and I. van | + | [[[RFC6147]]] Bagnulo, M., Sullivan, A., Matthews, P., and I. van |
Beijnum, "DNS64: DNS Extensions for Network Address | Beijnum, "DNS64: DNS Extensions for Network Address | ||
| − | Translation from IPv6 Clients to IPv4 Servers", | + | Translation from IPv6 Clients to IPv4 Servers", RFC 6147, |
DOI 10.17487/RFC6147, April 2011, | DOI 10.17487/RFC6147, April 2011, | ||
<https://www.rfc-editor.org/info/rfc6147>. | <https://www.rfc-editor.org/info/rfc6147>. | ||
| − | [[RFC6877]] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: | + | [[[RFC6877]]] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT: |
Combination of Stateful and Stateless Translation", | Combination of Stateful and Stateless Translation", | ||
| − | + | RFC 6877, DOI 10.17487/RFC6877, April 2013, | |
<https://www.rfc-editor.org/info/rfc6877>. | <https://www.rfc-editor.org/info/rfc6877>. | ||
| − | [[RFC7225]] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the | + | [[[RFC7225]]] Boucadair, M., "Discovering NAT64 IPv6 Prefixes Using the |
| − | Port Control Protocol (PCP)", | + | Port Control Protocol (PCP)", RFC 7225, |
DOI 10.17487/RFC7225, May 2014, | DOI 10.17487/RFC7225, May 2014, | ||
<https://www.rfc-editor.org/info/rfc7225>. | <https://www.rfc-editor.org/info/rfc7225>. | ||
| − | [[RFC7556]] Anipko, D., Ed., "Multiple Provisioning Domain | + | [[[RFC7556]]] Anipko, D., Ed., "Multiple Provisioning Domain |
| − | Architecture", | + | Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015, |
<https://www.rfc-editor.org/info/rfc7556>. | <https://www.rfc-editor.org/info/rfc7556>. | ||
| − | [[RFC7858]] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., | + | [[[RFC7858]]] Hu, Z., Zhu, L., Heidemann, J., Mankin, A., Wessels, D., |
and P. Hoffman, "Specification for DNS over Transport | and P. Hoffman, "Specification for DNS over Transport | ||
| − | Layer Security (TLS)", | + | Layer Security (TLS)", RFC 7858, DOI 10.17487/RFC7858, May |
2016, <https://www.rfc-editor.org/info/rfc7858>. | 2016, <https://www.rfc-editor.org/info/rfc7858>. | ||
| − | [[RFC8305]] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: | + | [[[RFC8305]]] Schinazi, D. and T. Pauly, "Happy Eyeballs Version 2: |
| − | Better Connectivity Using Concurrency", | + | Better Connectivity Using Concurrency", RFC 8305, |
DOI 10.17487/RFC8305, December 2017, | DOI 10.17487/RFC8305, December 2017, | ||
<https://www.rfc-editor.org/info/rfc8305>. | <https://www.rfc-editor.org/info/rfc8305>. | ||
| − | [[RFC8484]] Hoffman, P. and P. McManus, "DNS Queries over HTTPS | + | [[[RFC8484]]] Hoffman, P. and P. McManus, "DNS Queries over HTTPS |
| − | (DoH)", | + | (DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018, |
<https://www.rfc-editor.org/info/rfc8484>. | <https://www.rfc-editor.org/info/rfc8484>. | ||
Revision as of 10:37, 25 October 2020
Internet Engineering Task Force (IETF) L. Colitti Request for Comments: 8781 J. Linkova Category: Standards Track Google ISSN: 2070-1721 April 2020
Discovering PREF64 in Router Advertisements
Abstract
This document specifies a Neighbor Discovery option to be used in Router Advertisements (RAs) to communicate prefixes of Network Address and Protocol Translation from IPv6 clients to IPv4 servers (NAT64) to hosts.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at https://www.rfc-editor.org/info/rfc8781.
Copyright Notice
Copyright (c) 2020 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 (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.
1. Introduction
1.1. Requirements Language 1.2. Terminology
2. Use Cases for Communicating the NAT64 Prefix to Hosts 3. Why Include the NAT64 Prefix in Router Advertisements? 4. Option Format
4.1. Scaled Lifetime Processing
5. Usage Guidelines
5.1. Handling Multiple NAT64 Prefixes 5.2. PREF64 Consistency
6. IANA Considerations 7. Security Considerations 8. References
8.1. Normative References 8.2. Informative References
Acknowledgements Authors' Addresses
Contents
Introduction
NAT64 [[[RFC6146]]] with DNS Extensions for Network Address Translation from IPv6 clients to IPv4 servers (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 Neighbor Discovery [[[RFC4861]]] option to be used in Router Advertisements (RAs) to communicate NAT64 prefixes to hosts.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [[[RFC2119]]] [[[RFC8174]]] when, and only when, they appear in all capitals, as shown here.
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]]];
Router Advertisement (RA): 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]]];
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:
- 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." Therefore, to perform the DNS64 function, the
stub resolver needs to know the NAT64 prefix. 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 [[[RFC7858]]] or DNS-over-HTTPS [[[RFC8484]]] server
with which the host has an existing trust relationship).
- Networks with no DNS64 server. Hosts that support AAAA
synthesis and are aware of the NAT64 prefix in use do not need
the network to perform the DNS64 function at all.
- 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.
Why Include the NAT64 Prefix in Router Advertisements?
Fate sharing: NAT64 requires routing to be configured. IPv6 routing
configuration requires receiving an IPv6 RA [[[RFC4861]]]. Therefore, using RAs to provide hosts with the NAT64 prefix ensures that NAT64 reachability information shares the fate of the rest of the network configuration on the host.
Atomic configuration: Including the NAT64 prefix in the RA minimizes
the number of packets required to configure a host. Only one packet (an RA) is required to complete the network configuration. This speeds up the process of connecting to a network that supports NAT64/DNS64. It also 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 RA.
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., Port Control Protocol (PCP) [[[RFC7225]]]), which could be considered an obstacle for deployment.
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 | Scaled Lifetime | PLC | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | + + | Highest 96 bits of the Prefix | + + | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NAT64 Prefix Option Format
Fields:
Type: 8-bit identifier of the PREF64 option type (38)
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.
Scaled Lifetime: 13-bit unsigned integer. The maximum time in units
of 8 seconds over which this NAT64 prefix MAY be used. See Section 4.1 for the Scaled Lifetime field processing rules.
PLC (Prefix Length Code): 3-bit unsigned integer. This field
encodes the NAT64 Prefix Length defined in [[[RFC6052]]]. The PLC field values 0, 1, 2, 3, 4, and 5 indicate the NAT64 prefix length of 96, 64, 56, 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 bits of the Prefix: 96-bit unsigned integer. Contains
bits 0 - 95 of the NAT64 prefix.
Scaled Lifetime Processing
It would be highly undesirable for the NAT64 prefix to have a lifetime shorter than the Router Lifetime, which is defined in Section 4.2 of [[[RFC4861]]] as a 16-bit unsigned integer. If the NAT64 prefix lifetime is not at least equal to the default Router Lifetime, it might lead to scenarios in which the NAT64 prefix lifetime expires before the arrival of the next unsolicited RA. Therefore, the Scaled Lifetime encodes the NAT64 prefix lifetime in units of 8 seconds. The receiver MUST multiply the Scaled Lifetime value by 8 (for example, by a logical left shift) to calculate the maximum time in seconds the prefix MAY be used. The maximum lifetime of the NAT64 prefix is thus 65528 seconds. To ensure that the NAT64 prefix does not expire before the default router, it is NOT RECOMMENDED to configure default Router Lifetimes greater than 65528 seconds when using this option. A lifetime of 0 indicates that the prefix SHOULD NOT be used anymore.
By default, the value of the Scaled Lifetime field SHOULD be set to the lesser of 3 x MaxRtrAdvInterval [[[RFC4861]]] divided by 8, or 8191.
Router vendors SHOULD allow administrators to specify nonzero lifetime values that are not divisible by 8. In such cases, the router SHOULD round the provided value up to the nearest integer that is divisible by 8 and smaller than 65536, then divide the result by 8 (or perform a logical right shift by 3) and set the Scaled Lifetime field to the resulting value. If a nonzero lifetime value that is to be divided by 8 (or subjected to a logical right shift by 3) is less than 8, then the Scaled Lifetime field SHOULD be set to 1. This last step ensures that lifetimes under 8 seconds are encoded as a nonzero Scaled Lifetime.
Usage Guidelines
This option specifies exactly one NAT64 prefix for all IPv4 destinations. If the network operator wants to route different parts of the IPv4 address space to different NAT64 devices, this can be accomplished by routing more specific subprefixes of the NAT64 prefix to those devices. For example, suppose an operator is using the [[[RFC1918]]] address space 10.0.0.0/8 internally. That operator might want to route 10.0.0.0/8 through NAT64 device A, and the rest of the IPv4 space through NAT64 device B. If 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::/96 to NAT64 B.
This option may appear more than once in an RA (e.g., when gracefully renumbering the network from one NAT64 prefix to another). Host behavior with regard to synthesizing IPv6 addresses from IPv4 addresses SHOULD follow the recommendations given in Section 3 of [[[RFC7050]]], limited to the NAT64 prefixes that have a nonzero 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 that 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: the host in an IPv6-only network does not have an IPv4 address and cannot reach any IPv4 destinations without the NAT64.
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):
- the host is using multiple mechanisms to discover PREF64 prefixes
(e.g., by using PCP [[[RFC7225]]]) and/or resolving an IPv4-only fully qualified domain name [[[RFC7050]]] in addition to receiving the PREF64 RA option);
- the PREF64 option presents in a single RA more than once;
- the host receives multiple RAs with different PREF64 prefixes on a
given interface.
When multiple PREF64s are discovered via the RA PREF64 Option (either the Option presents more than once in a single RA or multiple RAs are received), host behavior with regard to synthesizing IPv6 addresses from IPv4 addresses SHOULD follow the recommendations given in Section 3 of [[[RFC7050]]], limited to the NAT64 prefixes that have a nonzero lifetime.
When different PREF64s are discovered using multiple mechanisms, hosts SHOULD select one source of information only. The RECOMMENDED order is:
- PCP-discovered prefixes [[[RFC7225]]], if supported;
- PREF64s discovered via the RA Option;
- PREF64s resolving an IPv4-only fully qualified domain name
[[[RFC7050]]]
Note: If the network provides PREF64s via both this RA Option and [[[RFC7225]]], hosts that receive the PREF64 via the RA Option may choose to use it immediately (before waiting for the PCP to complete); therefore, some traffic may not reflect any more detailed configuration provided by the PCP.
The host SHOULD treat the PREF64 as being specific to the network interface it was received on. Hosts that are aware of Provisioning Domain (PvD, [[[RFC7556]]]) MUST treat the PREF64 as being scoped to the implicit or explicit PvD.
PREF64 Consistency
Section 6.2.7 of [[[RFC4861]]] recommends that routers inspect RAs sent by other routers to ensure that all routers onlink advertise 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:
- set of PREF64s with a nonzero lifetime;
- set of PREF64s with a zero lifetime.
Routers that are aware of PvD ([[[RFC7556]]]) MUST only compare information scoped to the same implicit or explicit PvD.
IANA Considerations
IANA has assigned a new IPv6 Neighbor Discovery Option type for the PREF64 option defined in this document in the "IPv6 Neighbor Discovery Option Formats" registry [IANA].
+---------------+------+
| Description | Type |
+===============+======+
| PREF64 option | 38 |
+---------------+------+
Table 1: New IANA
Registry Assignment
Security Considerations
Because RAs are required in all IPv6 configuration scenarios, on IPv6-only networks, RAs must already be secured -- e.g., by deploying an RA-Guard [[[RFC6105]]]. Providing all configuration in RAs reduces the attack surface to be targeted by malicious attackers trying to provide hosts with invalid configuration, as compared to distributing the configuration through multiple different mechanisms that need to be secured independently.
If a host is provided with an incorrect NAT64 prefix, the IPv6-only host might not be able to communicate with IPv4-only destinations. Connectivity to destinations reachable over IPv6 would not be impacted just by providing a host with an incorrect prefix; however, if attackers are capable of sending rogue RAs, they can perform denial-of-service or man-in-the-middle attacks, as described in [[[RFC6104]]].
The security measures that must already be in place to ensure that RAs are only received from legitimate sources eliminate the problem of NAT64 prefix validation described in Section 3.1 of [[[RFC7050]]].
References
Normative References
[IANA] IANA, "Internet Control Message Protocol version 6
(ICMPv6) Parameters",
<https://www.iana.org/assignments/icmpv6-parameters>.
[[[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>.
[[[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>.
[[[RFC8174]]] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Informative References
[[[RFC1918]]] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[[[RFC6104]]] Chown, T. and S. Venaas, "Rogue IPv6 Router Advertisement
Problem Statement", RFC 6104, DOI 10.17487/RFC6104,
February 2011, <https://www.rfc-editor.org/info/rfc6104>.
[[[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>.
[[[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>.
[[[RFC8484]]] Hoffman, P. and P. McManus, "DNS Queries over HTTPS
(DoH)", RFC 8484, DOI 10.17487/RFC8484, October 2018,
<https://www.rfc-editor.org/info/rfc8484>.
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, Benjamin Kaduk, Erik Kline, Suresh Krishnan, Warren Kumari, David Lamparter, Barry Leiba, Jordi Palet Martinez, Tommy Pauly, Alexandre Petrescu, Michael Richardson, David Schinazi, Ole Troan, Eric Vynke, Bernie Volz.
Authors' Addresses
Lorenzo Colitti Google Shibuya 3-21-3, Tokyo 150-0002 Japan
Email: [email protected]
Jen Linkova Google 1 Darling Island Rd Pyrmont NSW 2009 Australia
Email: [email protected]
