DNS-Based Address Mapping Record (AMR) for IPv4/IPv6 Mapping in IPv6-only Networks
draft-dong-dnsop-dns-record-amr-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Authors | Guozhen Dong , Chongfeng Xie | ||
| Last updated | 2026-05-22 | ||
| RFC stream | (None) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
| Telechat date | (None) | ||
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| Send notices to | (None) |
draft-dong-dnsop-dns-record-amr-01
DNSOP Working Group G. Dong
Internet-Draft C. Xie
Intended status: Standards Track China Telecom
Expires: 23 November 2026 22 May 2026
DNS-Based Address Mapping Record (AMR) for IPv4/IPv6 Mapping in
IPv6-only Networks
draft-dong-dnsop-dns-record-amr-01
Abstract
This document defines a new Domain Name System (DNS) resource record
type called the Address Mapping Record (AMR). The AMR record enables
querying of IPv6 mapping prefixes associated with the destination
address of an IPv4 packet in IPv6-only networks. This mechanism
facilities the transmission of IPv4 service data across multi-domain
in IPv6-only environment, supporting IPv4-as-a-Service (IPv4aaS)
implementations.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 23 November 2026.
Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. AMR Record Format . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Record Name Construction . . . . . . . . . . . . . . . . 3
4.2. AMR Encoding . . . . . . . . . . . . . . . . . . . . . . 3
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5.1. Mapping Relationship Registration . . . . . . . . . . . . 7
5.2. AMR Record Publication in Global DNS . . . . . . . . . . 7
5.3. Procedure for Ingress PE to Query IPv6 Mapping Prefix for a
Specific IPv4 Address via DNS . . . . . . . . . . . . . . 7
5.4. Delegation and Management of in-addr-m.arpa . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7.1. Allocation of AMR Resource Record Type . . . . . . . . . 10
7.2. Creation and Delegation of in-addr-m.arpa . . . . . . . . 10
7.3. DNS PARAMETERS Registry Update . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
[I-D.ietf-v6ops-framework-md-ipv6only-underlay] describes a framework
for deploying IPv6-only underlay in multi-domain networks, IPv4
packets are statelessly translated or encapsulated into IPv6 packets
for transmission. This framework requires IPv4/IPv6 address mapping
rule to support stateless packet conversion at Provider Edge (PE)
routers.
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This document defines a new Domain Name System (DNS) resource record
type, called the Address Mapping Record (AMR). AMR record
stores the mappings between IPv4 address blocks and their
corresponding IPv6 prefixes, enabling PE to query these mappings via
standard DNS protocols. AMR is applicable in IPv6-only networks
[I-D.ietf-v6ops-framework-md-ipv6only-underlay].
2. Conventions used in this document
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 [RFC2119] .
3. Terminology
The following terms are defined in this draft:
* DNS: Domain Name System, defined in [RFC1034][RFC1035]
* PE: Provider Edge, defined in [RFC4026]
* Pref6: IPv6 Mapping Prefix, indicating edge devices for
translating IPv4 packets in an IPv6-only network.
4. AMR Record Format
4.1. Record Name Construction
AMR records use a special domain name space under “in-addr-m.arpa”.
For an IPv4 address block 192.0.2.0/24, the corresponding AMR record
name is constructed by reversing the IPv4 prefix and appending ".in-
addr-m.arpa". Example:
IPv4 block: 192.0.2.0/24
IPv6 mapping prefix: 2001:db8::/64
The AMR record: 0.2.0.192.in-addr-m.arpa. IN AMR 2001:db8::/64
4.2. AMR Encoding
The encoding of the type is shown below：
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+----------------------------------------+
| Name (variable) |
+----------------------------------------+
| Type (2 octets) |
+----------------------------------------+
| Class (2 octets) |
+----------------------------------------+
| TTL (4 octets) |
+----------------------------------------+
| Data Length (2 octets) |
+----------------------------------------+
| v4prefix-length (1 octet) |
+----------------------------------------+
| v6prefix-length (1 octet) |
+----------------------------------------+
| v6prefix (0...16 octets) |
+----------------------------------------+
Figure 1: Format of AMR Record
Name— the reverse IPv4 address, its format is IPv4 address
block.in-addr-m.arpa;
Type— the type of the record，AMR;
Class— indicating that the record is for the Internet environment;
TTL—time-to-live in cache;
Data length— length of the data section;
v4prefix-length— length of the IPv4 address block;
v6prefix-length— length of the IPv6 mapping prefix;
v6prefix— IPv6 mapping prefix.
5. Operation
In a multi-domain IPv6-only network architecture, PE1 and PE2 are
network edge devices with rule-based IPv4-IPv6 conversion
capabilities, and their address mapping prefixes are denoted as
Pref6. Each edge device also needs to be associated with one or more
IPv4 address blocks, which are extracted from the local IPv4 routing
table or address pool. IPv4 packets enter the multi-domain IPv6-only
network via an ingress PE and exit via an egress PE. The mapping
relationship between an IPv4 address block and its corresponding IPv6
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prefix is referred ro as a mapping rule, which will have at least the
following data structure.
IPv4 address block: Pref6(PE)
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Global DNS System
|<---------------------->|
| |
| |
+------------------+ +-------------------+
| | 2.publish AMR | |
| |--------------------->| |
| |<---------------------| |
| Authoritative |5.TTL expire, query | Local DNS Server |
| DNS Server | the latest record | |
| | | |
| | | |
| |--------------------->| |
| |6.reply the lastest | |
| | AMR | |
+------------------+ +-------------------+
^ ^|
1.| ||
r | ||
e | ||
g | 3.||4.
i | q ||r
s | u ||e
t | e ||p
r | r ||l
a | y ||y
t | ||
i | ||
o | ||
n | ||
+-+------------------------------++-+
| | || |
| | +-+ +-+ +-+ || |
+----------+ | | /AS1\ /AS2\ /AS3\ || | +----------+
|IPv4 | | | | | | | | ||V | |IPv4 |
|network N1|---+-PE1 P1--P2 P3--P4 PE2-+---|network N2|
+----------+ | | | | | | | | +----------+
| \ / \ / \ / |
| +-+ +-+ +-+ |
| |
| Multi-domain IPv6-only Network |
+-----------------------------------+
Figure 2: The Option B cross-domain scenario
The AMR mechanism enables the distribution and retrieval of these
mappings via DNS, as detailed below.
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5.1. Mapping Relationship Registration
PE1 router generate mappings between local IPv4 address blocks
(served by their connected IPv4 networks) and their own IPv6 mapping
prefixes (Pref6). Then, PE1 send these mappings to an authoritative
DNS server, which stores them as AMR records in its database. The
authoritative server validates the format of the mappings (e.g.,
correct prefix lengths, valid IPv6 prefixes) before adding them to
the appropriate zone file under in-addr-m.arpa.
5.2. AMR Record Publication in Global DNS
Authoritative DNS servers publish AMR records within their managed
DNS zones, making them available for query by local DNS servers. AMR
records are assigned a TTL value (e.g., 3600 seconds) to control
cache freshness. Local DNS servers cache AMR records and refresh
them by querying the authoritative server once the TTL expires,
ensuring up-to-date mappings.
5.3. Procedure for Ingress PE to Query IPv6 Mapping Prefix for a
Specific IPv4 Address via DNS
When Ingress PE receives an IPv4 packet, it queries the DNS to
retrieve the corresponding IPv6 mapping prefix. The procedure is as
follows:
1. Extracts destination IPv4 address (e.g., 192.0.2.1).
2. Query Construction:
Ingress PE constructs a DNS query using the reversed destination
IPv4 address appended with .in-addr-m.arpa and specifies
the AMR record type. For example, a destination IPv4 address of
192.0.2.1 (within 192.0.2.0/24) results in the query name
1.2.0.192.in-addr-m.arpa IN AMR.
3. Query Resolution:
a. Checks local DNS cache for existing AMR record:
i. If valid cached record exists with unexpired TTL:
— Uses the cached IPv6 prefix for packet conversion;
— Skips further DNS queries.
ii. If no valid cache entry exists:
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— Proceeds to step 3b.
b. Performs DNS longest-prefix match lookup for the destination
IPv4 address using the following iterative procedure:
Let the destination IPv4 address be A.B.C.D (four octets).
For N from 4 down to 1:
- Construct a domain name using the least significant N
octets of the IPv4 address in reverse order, appended
with "in-addr-m.arpa".
Example for destination 192.0.2.1(octets 192, 0, 2, 1):
N=4: 1.2.0.192.in-addr-m.arpa
N=3: 2.0.192.in-addr-m.arpa
N=2: 0.192.in-addr-m.arpa
N=1: 192.in-addr-m.arpa
- Send a DNS query for type AMR for the constructed name.
If a non-empty AMR record is returned (NOERROR with at
least one answei), the associated IPv6 prefix is used
for packet conversion, and the procedure terminates.
If NxDOMAIN or NOERROR with zero answers is returned,
continue to the next smaller N.
If no AMR record is found for any N, the destination IPv4
address has no mapping, and the packet SHOULD be dropped
or handled according to local policy (e.g., fallback to
stateful translation.)
c. If the local resolver does not have the answer, it initiates
standard DNS resolution via recursive lookup as follows:
i. Follows normal DNS resolution chain.
ii. Queries authoritative servers for in-addr-m.arpa.
iii. Validates DNSSEC signatures if present.
4. Cache Refresh:
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When the TTL of a cached AMR record expires, the local server re-
queries the authoritative server to fetch the latest record,
updating its cache accordingly.
5.4. Delegation and Management of in-addr-m.arpa
The AMR mechanism relies on the reverse mapping domain "in-addr-
m.arpa". The delegation and management of this domain MUST follow a
well-defined hierarchy.
This document proposes that the delegation model for in-addr-m.arpa
SHALL mirror that of in-addr.arpa:
- The "arpa" domain is managed by IANA. IANA delegates the top-
level "in-addr-m.arpa" zone.
- Delegations under "in-addr-m.arpa" SHALL correspond to the IPv4
address allocation hierarchy. Specifically, each Regional
Internet Registry (RIR) is responsible for delegations under the
subdomain corresponding to the /8 IPv4 address blocks it manages.
For example, for the 192.0.0.0/8 block, the responsible RIR (e.g.,
APNIC) manages delegations under 192.in-addr-m.arpa.
- RIRs MAY further delegate subdomains to their members (e.g., ISPs
or end users) following existing reverse DNS delegation
procedures, such as those documented in [RFC2317] for classless
delegations.
Note (Open Issue): As of this version of the draft, the authors have
not yet formally consulted with the RIRs regarding the delegation and
management of "in-addr-m.arpa". The authors intend to initiate such
discussions once the technical approach has received initial feedback
from the DNSOP Working Group.
If RIR coordination proves infeasible, AMR can still be deployed
within a single administrative domain (e.g., an ISP's internal DNS)
without global in-addr-m.arpa delegation. This document describes
the global delegation model as the preferred approach but does not
preclude private/internal deployments.
6. Security Considerations
The AMR mechanism introduces several security considerations:
* Attackers could provide false mapping information. DNSSEC
[RFC4033] MUST be used to authenticate AMR record.
* Rate limiting SHOULD be implemented for AMR queries.
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7. IANA Considerations
This document defines a new DNS Resource Record type - Address
Mapping Record (AMR) from the "DNS PARAMETERS" registry.
7.1. Allocation of AMR Resource Record Type
IANA is requested to allocate a new DNS Resource Record Type code for
the Address Mapping Record (AMR) from the "Resource Record (RR)
TYPEs" registry under the "Domain Name System (DNS) Parameters" group
[IANA-DNS-PARAMETERS].
Type: AMR
Value: TBD (to be assigned by IANA)
Meaning: Address Mapping Record
7.2. Creation and Delegation of in-addr-m.arpa
IANA is requested to create the reverse mapping zone "in-addr-m.arpa"
under the "arpa" domain. The delegation policies for this zone are
to be defined in coordination with the Regional Internet Registries
(RIRs) and will be documented in a separate specification or an
updated version of this document.
This may require registration of "in-addr-m.arpa" as a Special-
Purpose Domain under the "Special-Use Domain Names" registry
[RFC6761]. The authors will coordinate with IANA and the RIRs to
determine the appropriate registration status prior to publication.
7.3. DNS PARAMETERS Registry Update
No other parameters are requested from the DNS PARAMETERS registry at
this time.
8. Acknowledgements
This comments and suggestions of the following are gratefully
acknowledged:
* TBD
9. References
9.1. Normative References
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[RFC1034] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
<https://www.rfc-editor.org/info/rfc1034>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/info/rfc1035>.
[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>.
[RFC4026] Andersson, L. and T. Madsen, "Provider Provisioned Virtual
Private Network (VPN) Terminology", RFC 4026,
DOI 10.17487/RFC4026, March 2005,
<https://www.rfc-editor.org/info/rfc4026>.
[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>.
9.2. Informative References
[I-D.ietf-v6ops-framework-md-ipv6only-underlay]
Xie, C., Ma, C., Li, X., Mishra, G. S., and T. Graf,
"Framework for Multi-domain IPv6-only Underlay Network and
IPv4-as-a-Service", Work in Progress, Internet-Draft,
draft-ietf-v6ops-framework-md-ipv6only-underlay-22, 8 May
2026, <https://datatracker.ietf.org/doc/html/draft-ietf-
v6ops-framework-md-ipv6only-underlay-22>.
[RFC6761] Cheshire, S. and M. Krochmal, "Special-Use Domain Names",
RFC 6761, DOI 10.17487/RFC6761, February 2013,
<https://www.rfc-editor.org/info/rfc6761>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>.
Authors' Addresses
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Guozhen Dong
China Telecom
Beiqijia Town, Changping District
Beijing
Beijing, 102209
China
Email: guozhen.dong@foxmail.com
Chongfeng Xie
China Telecom
Beiqijia Town, Changping District
Beijing
Beijing, 102209
China
Email: xiechf@chinatelecom.cn
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