SNAC Router Flag in ICMPv6 Router Advertisement Messages

Introduction 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 to a home network, automatically providing IPv6 forwarding between the two networks without explicit operator configuration. SNAC routers are described in . 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.

Terminology 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 when, and only when, they appear in all capitals, as shown here.

SNAC Router Flag The "SNAC Router" flag is bit TBD in the RA Flags Extension Option . The SNAC router flag with value '1' is reserved for use by SNAC routers. The definition of what a SNAC router and when a SNAC router sets this flag is is out of scope for this document. The SNAC router specification work in progress can be seen here: . As defined by , 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 Considerations IANA is requested to allocate a flag from the "Internet Control Message Protocol version 6 (ICMPv6) Parameters", "IPv6 ND Router Advertisement flags" registry as specified below:

RA Option Bit	Description	Reference
TBD	S - SNAC Router Flag	This Document

Security Considerations How SNAC routers process RAs is dependent on the SNAC router flag value. The security considerations for SNAC routers processing the SNAC router flag are documented in . The security considerations of IPv6 ND are documented in the "Security Considerations" section of . The addition of the SNAC router flag does not change these considerations. In environments that implement RA-Guard 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.