Internet Engineering Task Force M. Smith Internet-Draft May 4, 2021 Updates: 4861 (if approved) Intended status: Standards Track Expires: November 5, 2021 More Accurately Naming IPv6 RA Router Lifetime draft-smith-6man-accurate-ra-router-lifetime-00 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 November 5, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. 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 Smith Expires November 5, 2021 [Page 1]
Internet-DrafMore Accurately Naming IPv6 RA Router Lifetime May 2021 include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified 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. Change Log [RFC Editor please remove] . . . . . . . . . . . . 4 7. Informative References . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4 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, 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. Router Advertisements can carry options such as the Prefix Information option. These options are required to have their own lifetime fields if necessary [RFC4861]. 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 Smith Expires November 5, 2021 [Page 2]
Internet-DrafMore Accurately Naming IPv6 RA Router Lifetime May 2021 to indicate that the RA is entirely invalid and that all of its contents should or must be ignored 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." No other updates are needed, as the Default Router List host conceptual data structure, and the AdvDefaultLifetime router interface configuration variable, already use "default" terminology. 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. 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 link and path to a specific destination. Within these RAs is a Route Information Option (RIO) [RFC4191], specifying an IPv6 prefix covering the IPv6 address space reachable over the other link and path. 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. Smith Expires November 5, 2021 [Page 3]
Internet-DrafMore Accurately Naming IPv6 RA Router Lifetime May 2021 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. 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. Change Log [RFC Editor please remove] draft-smith-6man-accurate-ra-router-lifetime-00, initial version, 2021-03-09 7. Informative References [RFC4191] Draves, R. and D. Thaler, "Default Router Preferences and More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191, November 2005, <https://www.rfc-editor.org/info/rfc4191>. [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>. Author's Address Mark Smith PO BOX 521 HEIDELBERG, VIC 3084 AU Email: markzzzsmith@gmail.com Smith Expires November 5, 2021 [Page 4]