SNAC Router Flag in ICMPv6 Router Advertisement Messages
draft-ietf-6man-snac-router-ra-flag-06

Internet Engineering Task Force                                   J. Hui
Internet-Draft                                                Google LLC
Intended status: Standards Track                            8 April 2026
Expires: 10 October 2026

        SNAC Router Flag in ICMPv6 Router Advertisement Messages
                 draft-ietf-6man-snac-router-ra-flag-06

Abstract

   This document defines a new flag, the SNAC Router flag, in the Router
   Advertisement message that can be used to distinguish configuration
   information sent by SNAC routers from information sent by transit
   routers.

Status of This Memo

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   This Internet-Draft will expire on 10 October 2026.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  SNAC Router Flag  . . . . . . . . . . . . . . . . . . . . . .   2
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Operational Considerations  . . . . . . . . . . . . . . . . .   3
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   8.  Informative References  . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   Per Section 2.1 of [RFC2328], networks can either be transmit or stub
   networks.  Transit networks are those capable of carrying data
   traffic that is neither locally originated nor locally destined.

   A Stub Network Auto-Configuring (SNAC) router is an autonomously
   configuring router that provides IP connectivity between one or more
   stub networks and one or more transit networks.  A common SNAC router
   example is a device that attaches a 6LoWPAN-based network [RFC4919]
   to a home network, automatically providing IPv6 forwarding between
   the two networks without explicit operator configuration.  This
   document defines a new IPv6 ND Router Advertisement (RA) flag, the
   "SNAC router" flag, which SNAC routers use to identify RAs sent by
   other SNAC routers.

   Readers can refer to [I-D.ietf-snac-simple] for an overview of a set
   of practices for automatically connecting IPv6 stub networks to
   transmit networks.

2.  Terminology

   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.

3.  SNAC Router Flag

   The "SNAC Router" flag is bit TBD in the RA Flags Extension Option
   [RFC5175].

   The SNAC router flag bit with value '1' is reserved for use by SNAC
   routers.  Receipt of an RA with that bit set to 1 indicates that the
   sending router is a SNAC router.  Describing the exact triggers when

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   a SNAC router sets this flag to '1' is out of scope for this
   document.  An example of such considerations are documented in
   [I-D.ietf-snac-simple].

   Consistent with Section 4.2 of [RFC4861], devices that do not operate
   as SNAC routers will not set the SNAC router flag bit to '1', and
   routers that do not understand the SNAC router flag will silently
   ignore it.  This means that setting the flag bit to '1' or '0' should
   not change the behavior of such devices in any way (other than that
   it is permissible to log and cache the value of the flag bit as part
   of normal router advertisement processing, where applicable).

4.  IANA Considerations

   IANA is requested to allocate a flag from the "Internet Control
   Message Protocol version 6 (ICMPv6) Parameters", "IPv6 ND Router
   Advertisement flags" registry [IANA-RA-FLAGS] as specified below:

         +---------------+----------------------+---------------+
         | RA Option Bit | Description          | Reference     |
         +---------------+----------------------+---------------+
         | TBD           | S - SNAC Router Flag | This Document |
         +---------------+----------------------+---------------+

                                 Table 1

5.  Operational Considerations

   In environments that implement RA-Guard [RFC7113] in a way that
   filters RAs sent by SNAC routers, devices on the transit network will
   never receive an RA with the SNAC router flag bit set to '1'.

6.  Security Considerations

   How SNAC routers process RAs is dependent on the SNAC router flag
   value.

   The security considerations of IPv6 ND are documented in the
   "Security Considerations" section of [RFC4861].  The addition of the
   SNAC router flag does not change these considerations.

7.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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   [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>.

   [RFC5175]  Haberman, B., Ed. and R. Hinden, "IPv6 Router
              Advertisement Flags Option", RFC 5175,
              DOI 10.17487/RFC5175, March 2008,
              <https://www.rfc-editor.org/info/rfc5175>.

   [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>.

8.  Informative References

   [I-D.ietf-snac-simple]
              Lemon, T. and J. Hui, "Automatically Connecting Stub
              Networks to Unmanaged Infrastructure", Work in Progress,
              Internet-Draft, draft-ietf-snac-simple-08, 10 October
              2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
              snac-simple-08>.

   [IANA-RA-FLAGS]
              IANA, "IPv6 ND Router Advertisement flags",
              <https://www.iana.org/assignments/icmpv6-parameters/
              icmpv6-parameters.xhtml#icmpv6-parameters-11>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <https://www.rfc-editor.org/info/rfc2328>.

   [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
              over Low-Power Wireless Personal Area Networks (6LoWPANs):
              Overview, Assumptions, Problem Statement, and Goals",
              RFC 4919, DOI 10.17487/RFC4919, August 2007,
              <https://www.rfc-editor.org/info/rfc4919>.

   [RFC7113]  Gont, F., "Implementation Advice for IPv6 Router
              Advertisement Guard (RA-Guard)", RFC 7113,
              DOI 10.17487/RFC7113, February 2014,
              <https://www.rfc-editor.org/info/rfc7113>.

Author's Address

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   Jonathan Hui
   Google LLC
   1600 Amphitheatre Parkway
   Mountain View, California 940432
   United States of America
   Email: jonhui@google.com

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