



Internet Engineering Task Force (IETF)                         R. Bonica
Request for Comments: 9805                              Juniper Networks
Updates: 2711                                                  June 2025
Category: Standards Track                                               
ISSN: 2070-1721


     Deprecation of the IPv6 Router Alert Option for New Protocols

Abstract

   This document deprecates the IPv6 Router Alert option.  Protocols
   that use the IPv6 Router Alert option may continue to do so, even in
   future versions.  However, new protocols that are standardized in the
   future must not use the IPv6 Router Alert option.

   This document updates RFC 2711.

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/rfc9805.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction
   2.  Requirements Language
   3.  Issues Associated with the IPv6 Router Alert Option
   4.  Deprecation of the IPv6 Router Alert Option
   5.  Future Work
   6.  Security Considerations
   7.  IANA Considerations
   8.  References
     8.1.  Normative References
     8.2.  Informative References
   Appendix A.  Protocols That Use the IPv6 Router Alert Option
   Acknowledgements
   Author's Address

1.  Introduction

   In IPv6 [RFC8200], optional internet-layer information is encoded in
   separate headers that may be placed between the IPv6 header and the
   upper-layer header in a packet.  There is a small number of such
   extension headers, each one identified by a distinct Next Header
   value.

   One of these extension headers is called the Hop-by-Hop Options
   header.  The Hop-by-Hop Options header is used to carry optional
   information that may be examined and processed by every node along a
   packet's delivery path.

   The Hop-by-Hop Options header can carry one or more options.  Among
   these is the IPv6 Router Alert option [RFC2711].

   The IPv6 Router Alert option provides a mechanism whereby routers can
   know when to intercept datagrams not addressed to them without having
   to extensively examine every datagram.  The semantic of the IPv6
   Router Alert option is that "routers should examine this datagram
   more closely".  Excluding this option tells the router that there is
   no need to examine this datagram more closely.

   As explained below, the IPv6 Router Alert option introduces many
   issues.

   This document updates [RFC2711].  Implementers of protocols that
   continue to use the IPv6 Router Alert option can continue to
   reference [RFC2711] for IPv6 Router Alert option details.

2.  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.

3.  Issues Associated with the IPv6 Router Alert Option

   [RFC6398] identifies security considerations associated with the IPv6
   Router Alert option.  In a nutshell, the IP Router Alert Option does
   not provide a universal mechanism to accurately and reliably
   distinguish between IP Router Alert packets of interest and unwanted
   IP Router Alerts.  This creates a security concern because, short of
   appropriate router-implementation-specific mechanisms, the router's
   control plane is at risk of being flooded by unwanted traffic.

      |  NOTE: Many routers maintain separation between forwarding and
      |  control plane hardware.  The forwarding plane is implemented on
      |  high-performance Application-Specific Integrated Circuits
      |  (ASICs) and Network Processors (NPs), while the control plane
      |  is implemented on general-purpose processors.  Given this
      |  difference, the control plane is more susceptible to a Denial-
      |  of-Service (DoS) attack than the forwarding plane.

   [RFC6192] demonstrates how a network operator can deploy Access
   Control Lists (ACLs) that protect the control plane from DoS attacks.
   These ACLs are effective and efficient when they select packets based
   upon information that can be found in a fixed position.  However,
   they become less effective and less efficient when they must parse a
   Hop-by-Hop Options header, searching for the IPv6 Router Alert
   option.

   Network operators can address the security considerations raised in
   [RFC6398] by:

   *  Deploying the operationally complex and computationally expensive
      ACLs described in [RFC6192].

   *  Configuring their routers to ignore the IPv6 Router Alert option.

   *  Dropping or severely rate limiting packets that contain the Hop-
      by-Hop Options header at the network edge.

   These options become less viable as protocol designers continue to
   design protocols that use the IPv6 Router Alert option.

   [RFC9673] seeks to eliminate hop-by-hop processing on the control
   plane.  However, because of its unique function, the IPv6 Router
   Alert option is granted an exception to this rule.  One approach
   would be to deprecate the IPv6 Router Alert option, because current
   usage beyond the local network appears to be limited and packets
   containing Hop-by-Hop options are frequently dropped.  Deprecation
   would allow current implementations to continue using it, but its use
   could be phased out over time.

4.  Deprecation of the IPv6 Router Alert Option

   This document deprecates the IPv6 Router Alert option.  Protocols
   that use the IPv6 Router Alert option MAY continue to do so, even in
   future versions.  However, new protocols that are standardized in the
   future MUST NOT use the IPv6 Router Alert option.  Appendix A
   contains an exhaustive list of protocols that MAY continue to use the
   IPv6 Router Alert option.

   This document updates [RFC2711].

5.  Future Work

   A number of protocols use the IPv6 Router Alert option; these are
   listed in Appendix A.  The only protocols in Appendix A that have
   widespread deployment are Multicast Listener Discovery Version 2
   (MLDv2) [RFC9777] and Multicast Router Discovery (MRD) [RFC4286].
   The other protocols either have limited deployment, are experimental,
   or have no known implementation.

   It is left for future work to develop new versions of MLDv2 and MRD
   that do not rely on the IPv6 Router Alert option.  That task is out
   of scope for this document.

6.  Security Considerations

   This document mitigates all security considerations associated with
   the IPv6 Router Alert option.  These security considerations can be
   found in [RFC2711], [RFC6192], and [RFC6398].

7.  IANA Considerations

   IANA has marked the IPv6 Router Alert option as "DEPRECATED for New
   Protocols" in the "Destination Options and Hop-by-Hop Options"
   registry <https://www.iana.org/assignments/ipv6-parameters> and added
   this document as a reference.

   IANA has also made a note in the "IPv6 Router Alert Option Values"
   registry <https://www.iana.org/assignments/ipv6-routeralert-values>
   stating that the registry is closed for allocations and added a
   reference to this document.  The experimental codepoints in this
   registry have been changed to "Reserved" (i.e., they are no longer
   available for experimentation).

8.  References

8.1.  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>.

   [RFC2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
              RFC 2711, DOI 10.17487/RFC2711, October 1999,
              <https://www.rfc-editor.org/info/rfc2711>.

   [RFC6398]  Le Faucheur, F., Ed., "IP Router Alert Considerations and
              Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
              2011, <https://www.rfc-editor.org/info/rfc6398>.

   [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>.

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC9673]  Hinden, R. and G. Fairhurst, "IPv6 Hop-by-Hop Options
              Processing Procedures", RFC 9673, DOI 10.17487/RFC9673,
              October 2024, <https://www.rfc-editor.org/info/rfc9673>.

8.2.  Informative References

   [RFC1633]  Braden, R., Clark, D., and S. Shenker, "Integrated
              Services in the Internet Architecture: an Overview",
              RFC 1633, DOI 10.17487/RFC1633, June 1994,
              <https://www.rfc-editor.org/info/rfc1633>.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031,
              DOI 10.17487/RFC3031, January 2001,
              <https://www.rfc-editor.org/info/rfc3031>.

   [RFC3175]  Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
              "Aggregation of RSVP for IPv4 and IPv6 Reservations",
              RFC 3175, DOI 10.17487/RFC3175, September 2001,
              <https://www.rfc-editor.org/info/rfc3175>.

   [RFC3208]  Speakman, T., Crowcroft, J., Gemmell, J., Farinacci, D.,
              Lin, S., Leshchiner, D., Luby, M., Montgomery, T., Rizzo,
              L., Tweedly, A., Bhaskar, N., Edmonstone, R.,
              Sumanasekera, R., and L. Vicisano, "PGM Reliable Transport
              Protocol Specification", RFC 3208, DOI 10.17487/RFC3208,
              December 2001, <https://www.rfc-editor.org/info/rfc3208>.

   [RFC4080]  Hancock, R., Karagiannis, G., Loughney, J., and S. Van den
              Bosch, "Next Steps in Signaling (NSIS): Framework",
              RFC 4080, DOI 10.17487/RFC4080, June 2005,
              <https://www.rfc-editor.org/info/rfc4080>.

   [RFC4286]  Haberman, B. and J. Martin, "Multicast Router Discovery",
              RFC 4286, DOI 10.17487/RFC4286, December 2005,
              <https://www.rfc-editor.org/info/rfc4286>.

   [RFC5946]  Le Faucheur, F., Manner, J., Narayanan, A., Guillou, A.,
              and H. Malik, "Resource Reservation Protocol (RSVP)
              Extensions for Path-Triggered RSVP Receiver Proxy",
              RFC 5946, DOI 10.17487/RFC5946, October 2010,
              <https://www.rfc-editor.org/info/rfc5946>.

   [RFC5971]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
              Signalling Transport", RFC 5971, DOI 10.17487/RFC5971,
              October 2010, <https://www.rfc-editor.org/info/rfc5971>.

   [RFC5979]  Shen, C., Schulzrinne, H., Lee, S., and J. Bang, "NSIS
              Operation over IP Tunnels", RFC 5979,
              DOI 10.17487/RFC5979, March 2011,
              <https://www.rfc-editor.org/info/rfc5979>.

   [RFC6016]  Davie, B., Le Faucheur, F., and A. Narayanan, "Support for
              the Resource Reservation Protocol (RSVP) in Layer 3 VPNs",
              RFC 6016, DOI 10.17487/RFC6016, October 2010,
              <https://www.rfc-editor.org/info/rfc6016>.

   [RFC6192]  Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
              Router Control Plane", RFC 6192, DOI 10.17487/RFC6192,
              March 2011, <https://www.rfc-editor.org/info/rfc6192>.

   [RFC6401]  Le Faucheur, F., Polk, J., and K. Carlberg, "RSVP
              Extensions for Admission Priority", RFC 6401,
              DOI 10.17487/RFC6401, October 2011,
              <https://www.rfc-editor.org/info/rfc6401>.

   [RFC7506]  Raza, K., Akiya, N., and C. Pignataro, "IPv6 Router Alert
              Option for MPLS Operations, Administration, and
              Maintenance (OAM)", RFC 7506, DOI 10.17487/RFC7506, April
              2015, <https://www.rfc-editor.org/info/rfc7506>.

   [RFC8029]  Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
              Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
              Switched (MPLS) Data-Plane Failures", RFC 8029,
              DOI 10.17487/RFC8029, March 2017,
              <https://www.rfc-editor.org/info/rfc8029>.

   [RFC9570]  Kompella, K., Bonica, R., and G. Mirsky, Ed., "Deprecating
              the Use of Router Alert in LSP Ping", RFC 9570,
              DOI 10.17487/RFC9570, May 2024,
              <https://www.rfc-editor.org/info/rfc9570>.

   [RFC9777]  Haberman, B., Ed., "Multicast Listener Discovery Version 2
              (MLDv2) for IPv6", STD 101, RFC 9777,
              DOI 10.17487/RFC9777, March 2025,
              <https://www.rfc-editor.org/info/rfc9777>.

Appendix A.  Protocols That Use the IPv6 Router Alert Option

   Table 1 contains an exhaustive list of protocols that use the IPv6
   Router Alert option.  There are no known IPv6 implementations of MPLS
   Ping.  Neither Integrated Services (Intserv) nor Next Steps in
   Signaling (NSIS) are widely deployed.  All NSIS protocols are
   experimental.  Pragmatic Generic Multicast (PGM) is experimental, and
   there are no known IPv6 implementations.

   +=================+=============================+==================+
   | Protocol        | References                  | Application      |
   +=================+=============================+==================+
   | Multicast       | [RFC9777]                   | IPv6 Multicast   |
   | Listener        |                             |                  |
   | Discovery       |                             |                  |
   | Version 2       |                             |                  |
   | (MLDv2)         |                             |                  |
   +-----------------+-----------------------------+------------------+
   | Multicast       | [RFC4286]                   | IPv6 Multicast   |
   | Router          |                             |                  |
   | Discovery (MRD) |                             |                  |
   +-----------------+-----------------------------+------------------+
   | Pragmatic       | [RFC3208]                   | IPv6 Multicast   |
   | General         |                             |                  |
   | Multicast (PGM) |                             |                  |
   +-----------------+-----------------------------+------------------+
   | MPLS Ping (Use  | [RFC7506][RFC8029][RFC9570] | MPLS Operations, |
   | of the IPv6     |                             | Administration,  |
   | Router Alert    |                             | and Maintenance  |
   | option is       |                             | (OAM)            |
   | deprecated)     |                             |                  |
   +-----------------+-----------------------------+------------------+
   | Resource        | [RFC3175] [RFC5946]         | Integrated       |
   | Reservation     | [RFC6016] [RFC6401]         | Services         |
   | Protocol        |                             | (Intserv)        |
   | (RSVP): Both    |                             | [RFC1633] and    |
   | IPv4 and IPv6   |                             | Multiprotocol    |
   | implementations |                             | Label Switching  |
   |                 |                             | (MPLS) [RFC3031] |
   +-----------------+-----------------------------+------------------+
   | Next Steps in   | [RFC5979] [RFC5971]         | NSIS [RFC4080]   |
   | Signaling       |                             |                  |
   | (NSIS)          |                             |                  |
   +-----------------+-----------------------------+------------------+

         Table 1: Protocols That Use the IPv6 Router Alert Option

Acknowledgements

   Thanks to Zafar Ali, Brian Carpenter, Toerless Eckert, David Farmer,
   Adrian Farrel, Bob Hinden, and Jen Linkova for their reviews of this
   document.

Author's Address

   Ron Bonica
   Juniper Networks
   United States of America
   Email: rbonica@juniper.net
