Deprecation of the IPv6 Router Alert Option for New Protocols
updates
- rfc-2711 — IPv6 Router Alert Option
Extracted elements (14)
Deprecation was chosen over outright removal because current usage of the Router Alert option beyond the local network appears limited and packets containing Hop-by-Hop options are frequently dropped in practice; deprecation allows existing implementations to continue while phasing out new use over time.
Development of new versions of MLDv2 and MRD that do not rely on the IPv6 Router Alert option is explicitly deferred as future work outside the scope of this document, acknowledging these are the protocols most impacted by the deprecation.
RFC 9673 sought to eliminate hop-by-hop processing on the control plane but granted the Router Alert option an exception due to its unique function; deprecating the option removes the need for that exception going forward.
Appendix A enumerates all protocols grandfathered to continue using the Router Alert option: MLDv2, Multicast Router Discovery, PGM (experimental, no known IPv6 implementation), MPLS Ping (already deprecated by RFC 9570), RSVP, and NSIS (all experimental).
Implementers of protocols that continue to use the IPv6 Router Alert option (listed in Appendix A) may continue to reference RFC 2711 for option details; this document updates but does not fully supersede RFC 2711.
The only widely deployed protocols using the IPv6 Router Alert option are MLDv2 (RFC 9777) and Multicast Router Discovery (RFC 4286); other listed protocols have limited deployment, are experimental, or have no known implementation.
New protocols that are standardized in the future MUST NOT use the IPv6 Router Alert option. This is the core deprecation mandate introduced by this document.
Protocols that currently use the IPv6 Router Alert option MAY continue to do so, even in future versions of those protocols. The deprecation applies only to newly standardized protocols.
The IPv6 Router Alert option is carried in the Hop-by-Hop Options header and signals to routers that they should examine the datagram more closely, enabling interception of datagrams not addressed to them without examining every packet.
IANA has closed the 'IPv6 Router Alert Option Values' registry for new allocations and changed experimental codepoints to 'Reserved', making them no longer available for experimentation.
IANA has marked the IPv6 Router Alert option as 'DEPRECATED for New Protocols' in the 'Destination Options and Hop-by-Hop Options' registry at iana.org/assignments/ipv6-parameters, with this document added as a reference.
ACLs designed to protect the control plane from DoS (per RFC 6192) become less effective and computationally expensive when they must parse the Hop-by-Hop Options header to search for the Router Alert option, since the option is not at a fixed position.
The IPv6 Router Alert option does not provide a universal mechanism to accurately and reliably distinguish between wanted and unwanted Router Alert packets, exposing the router control plane to flooding by unwanted traffic and denial-of-service attacks.
This document mitigates all security considerations associated with the IPv6 Router Alert option previously identified in RFC 2711, RFC 6192, and RFC 6398 by deprecating future use of the option.