| Internet-Draft | Stub Router RA Flag | July 2022 |
| Hui | Expires 8 January 2023 | [Page] |
This document defines a new Stub Router flag in the Router Advertisement message to distinguish configuration information sent by stub routers from infrastructure routers. For example, the Stub Router flag allows stub routers to easily identify when an infrastructure router is advertising a usable IPv6 prefix, triggering the stub router to not advertise its own routable prefix.¶
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 8 January 2023.¶
Copyright (c) 2022 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 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.¶
A stub router provides IP connectivity between a stub network and an infrastructure network. A common stub router example is a device that attaches a 6LoWPAN-based network to a home network.¶
To support IPv6 reachability between infrastructure network devices and stub network devices, routable IPv6 addresses must be configured on both the infrastructure and stub networks. Routers on the infrastructure network may configure routable IPv6 prefixes using Router Advertisements (RAs) containing Prefix Information Options (PIOs) [RFC4861].¶
In cases where the infrastructure network does not provide routable IPv6 address configuration, the stub router is responsible for configuring routable IPv6 addresses on the infrastructure network. If a stub router determines that routable IPv6 addresses are not available on the infrastructure link, it will locally generate a Unique Local Address (ULA) Prefix [RFC4193] and begin advertising that via a PIO contained in RA messages.¶
Both infrastructure routers and stub routers may advertise routable IPv6 prefixes in the same way (via RAs containing PIOs). To distinguish between an infrastructure router and a stub router, this document defines a new Stub Router flag in the RA message. The Stub Router flag allows stub routers to easily identify when an infrastructure router is advertising a routable IPv6 prefix, triggering the stub router to stop advertising its ULA prefix.¶
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.¶
This document defines a new "Stub Router" flag as flag bit 8 in the Router Advertisement flags field. Setting the Stub Router flag requires use of the RA Flags Extension Option [RFC5175] to encode the flag.¶
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length |S| Bit fields available .. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... for assignment | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+¶
A stub router that is not explicitly configured as part of the infrastructure network MUST set the Stub Router flag in outgoing RA messages.¶
How and when a stub router includes PIOs in outgoing RAs is specified in [I-D.lemon-stub-networks].¶
IANA is requested to allocate a flag from the "IPv6 ND Router Advertisement flags" registry of [RFC5175], as specified below:¶
| RA Option Bit | Description | Reference |
| 8 | S - Stub Router Flag | This Document |
Note that RA Option Bit 8 requires use of the RA Flags Extension Option [RFC5175] to encode the flag.¶
This protocol shares the security issues of NDP that are documented in the "Security Considerations" section of [RFC4861].¶