| Internet-Draft | SNAC Router RA Flag | December 2024 |
| Hui | Expires 7 June 2025 | [Page] |
This document defines a new flag, the SNAC Router flag, in the Router Advertisement message that can be used to distinguish configuration information sent by SNAC routers from information sent by infrastructure routers. This flag is used only by SNAC routers and is ignored by all other devices.¶
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A Stub Network Auto-Configuring (SNAC) router is an autonomously configuring router that provides IP connectivity between one or more stub networks and one or more infrastructure networks. A common SNAC router example is a device that attaches a 6LoWPAN-based network [RFC4919] to a home network, automatically providing IPv6 forwarding between the two networks without explicit operator configuration. SNAC routers are described in [I-D.ietf-snac-simple]. This document defines a new IPv6 ND Router Advertisement (RA) flag, the "SNAC router" flag, which SNAC routers use to identify RAs sent by other SNAC routers.¶
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.¶
The "SNAC Router" flag is bit TBD in the RA Flags Extension Option [RFC5175].¶
The SNAC router flag is to be used by SNAC routers. SNAC routers and the use of this flag are specified in [I-D.ietf-snac-simple]. As defined by Section 4.2 of [RFC4861], devices that do not operate as SNAC routers will not set the SNAC router flag, and routers that do not understand the SNAC router flag will silently ignore it. This means that the presence or absence of the flag should not change the behavior of such devices in any way (other than that it is of course permissible to log and cache the value of the flag as part of normal router advertisement processing, where applicable).¶
IANA is requested to allocate a flag from the "Internet Control Message Protocol version 6 (ICMPv6) Parameters", "IPv6 ND Router Advertisement flags" registry [IANA-RA-FLAGS] as specified below:¶
| RA Option Bit | Description | Reference |
| TBD | S - SNAC Router Flag | This Document |
How SNAC routers process RAs is dependent on the SNAC router flag value, as specified in [I-D.ietf-snac-simple]. The security considerations for SNAC routers processing the SNAC router flag are documented in [I-D.ietf-snac-simple].¶
The security considerations of IPv6 ND are documented in the "Security Considerations" section of [RFC4861]. The addition of the SNAC router flag does not change these considerations.¶
In environments that implement RA-Guard [RFC7113] in a way that filters RAs sent by SNAC routers, devices on the infrastructure network will never receive an RA with the SNAC router flag set.¶