Internet Engineering Task Force M.R. Smith Internet-Draft 21 July 2026 Updates: 4861 (if approved) Intended status: Standards Track Expires: 22 January 2027 More Accurately Naming IPv6 RA Router Lifetime draft-smith-6man-accurate-ra-router-lifetime-01 Abstract IPv6 Router Advertisements (RAs) have a "Router Lifetime" field, which specifies how long the advertising router will act as a default router for the receiving hosts, unless refreshed with another advertisement. The field name "Router Lifetime" is quite general, and could easily be misunderstood to mean the bounded lifetime of all of the information contained in the RA. This memo more accurately renames this field "Default Router Lifetime". 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 22 January 2027. Copyright Notice Copyright (c) 2026 IETF Trust and the persons identified as the document authors. All rights reserved. Smith Expires 22 January 2027 [Page 1] Internet-Draft More Accurately Naming IPv6 RA Router Li July 2026 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Updates to RFC4861 . . . . . . . . . . . . . . . . . . . . . 3 3. Zero Value Default Router Lifetime Example Use Case . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.2. Informative References . . . . . . . . . . . . . . . . . 5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction According to [RFC4861], Router Advertisements (RAs) are used by IPv6 routers to [...] advertise their presence together with various link and Internet parameters either periodically, or in response to a Router Solicitation message. Router Advertisements contain prefixes that are used for determining whether another address shares the same link (on-link determination) and/or address configuration, a suggested hop limit value, etc. The Router Lifetime field of an RA indicates whether or not the advertising router will act as a default router for the receiving IPv6 hosts [RFC4861], and if so, for how many seconds it will perform that role, unless it is refreshed by a subsequent RA from the router. The router is identified by its sending interface's Link-Local address [RFC4861]. If the RA Router Lifetime field value is zero, it means that the router is not or will no longer be acting as a default router [RFC4861]. Smith Expires 22 January 2027 [Page 2] Internet-Draft More Accurately Naming IPv6 RA Router Li July 2026 The Router Lifetime field in IPv6 RAs is likely to be a carry over from the Lifetime field in Router Advertisements used in the IPv4 ICMP Router Discovery Protocol (IRDP) [RFC1256]. ICMP Router Discovery RAs only advertise default routers. IPv6 Router Advertisements have been generalised to carry other link and subnet parameter options, such as MTU and Prefix Information [RFC4861]. IPv6 Router Advertisements options are required to have their own lifetime fields if necessary [RFC4861]. They are not related to or in any way impacted by the Router Lifetime field value of the RA the options are carried within. As the field name "Router Lifetime" is quite general, and is a permanent field in a Router Advertisement, the purpose of this field can be easily misunderstood. It could easily be misinterpreted as a maximum lifetime value applying to all of the parameters and options in the RA, acting as a constraint on all other lifetime values within the RA and its options. A Router Lifetime value of zero could seem to indicate that the RA is entirely invalid and that all of its options contents must be ignored or invalidated by the receivers of the RA. This memo renames the Router Lifetime field to "Default Router Lifetime", more accurately and explicitly describing its purpose. 2. Updates to RFC4861 For all instances of the term "router lifetime", the term "default router lifetime" is to be used, independent of letter case. When the term "lifetime" is used in the context of an IPv6 Router Advertisment, implying "router lifetime", it will now imply "default router lifetime." 3. Zero Value Default Router Lifetime Example Use Case The use of a non-zero Default Router Lifetime is obvious; the router sending these RAs is willing to act as a default router for the receiving hosts. An example of a router sending a zero value Default Router Lifetime is as follows. Smith Expires 22 January 2027 [Page 3] Internet-Draft More Accurately Naming IPv6 RA Router Li July 2026 On a link, there is a router acting as a default router for the attached hosts. This router is providing forwarding to default, unspecified destinations, such as the IPv6 Internet. The router's RAs have a non-zero value Default Router Lifetime, such as the [RFC4861] AdvDefaultLifetime default value of 1800 seconds (30 minutes). Also attached to the link is another router that is sending RAs with a zero value Default Router Lifetime. This router is also attached to another physical or logical link to a specific destination, such as an IPsec VPN tunnel [RFC4301]. Within these RAs is a Route Information Option (RIO) [RFC4191], specifying an IPv6 prefix covering the IPv6 address space reachable over the other link. Hosts receiving these zero value Default Router Lifetime RAs, that understand the Route Information Option, will send packets towards destinations within the prefix directly to the RIO advertising router, benefitting from a more optimal forwarding path, and also removing traffic forwarding load from the link's default router. The router advertising itself as a default router will need to know about this other router and the address space reachable beyond it, so that it can forward traffic towards the the other link and path, for hosts that do not understand the Route Information Option and that will send all of their traffic to the non-zero Default Router Lifetime router. 4. Security Considerations Security vulnerabilties can be created if the purpose or function of a mechanism is misunderstood. Renaming the IPv6 RA Router Lifetime field "Default Router Lifetime" will make it clearer what the purpose and function of this field in IPv6 RAs is. 5. Acknowledgements Review and comments were provided by YOUR NAME HERE! This memo was prepared using the xml2rfc tool. 6. References 6.1. Normative References [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, . Smith Expires 22 January 2027 [Page 4] Internet-Draft More Accurately Naming IPv6 RA Router Li July 2026 6.2. Informative References [RFC1256] Deering, S., Ed., "ICMP Router Discovery Messages", RFC 1256, DOI 10.17487/RFC1256, September 1991, . [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, November 2005, . [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, . Author's Address Mark Smith PO BOX 521 HEIDELBERG VIC 3084 Australia Email: markzzzsmith@gmail.com Smith Expires 22 January 2027 [Page 5]