Internet DRAFT - draft-hui-stub-router-ra-flag
draft-hui-stub-router-ra-flag
Internet Engineering Task Force J. Hui
Internet-Draft Google LLC
Intended status: Standards Track 27 February 2024
Expires: 30 August 2024
Stub Router Flag in ICMPv6 Router Advertisement Messages
draft-hui-stub-router-ra-flag-02
Abstract
This document defines a new Stub Router flag in the Router
Advertisement message that can be used to distinguish configuration
information sent by stub routers from information sent by
infrastructure routers.
Status of This Memo
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This Internet-Draft will expire on 30 August 2024.
Copyright Notice
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Stub Router Flag . . . . . . . . . . . . . . . . . . . . . . 3
4. Router Advertisement Transmission . . . . . . . . . . . . . . 3
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 4
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 4
1. Introduction
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. Stub routers decide
whether or not to advertise their ULA prefixes [RFC4193] on the
infrastructure network to which they are connected by tracking the
presence of infrastructure-provided IPv6 service. When a stub router
sees a new prefix advertised on infrastructure, this prefix may be
coming from an infrastructure router, or from another stub router.
In the second case, the two stub routers could wind up in a cycle of
publishing and deprecating their prefixes as they see prefixes from
the other stub router show up.
The stub router document [I-D.ietf-snac-simple] explains how two stub
routers decide which one has precedence in the event of a conflict.
However, the infrastructure prefix always has precedence over a
prefix provided by any stub router. In order to differentiate
between prefixes advertised by infrastructure and those advertised by
stub routers, it is necessary to be able to mark RAs sent by stub
routers.
Additionally, the RA header includes M and O flags that indicate
whether DHCPv6 is available on the link. Section 6.3.4 of [RFC4861]
specifies that hosts consider the most recently received information
as authoritative. As a result, stub routers must mirror the M and O
values in RAs received from infrastructure routers. The Stub Router
flag allows stub routers to easily identify which RAs are sent by
infrastructure routers.
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2. 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 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Stub Router Flag
This document defines a new "Stub Router" flag as flag bit 6 in the
Router Advertisement flags field.
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Cur Hop Limit |M|O|H|Prf|P|S|R| Router Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reachable Time |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Retrans Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options ...
+-+-+-+-+-+-+-+-+-+-+-+-
Figure 1: outer Advertisement Message Format
The S flag is the "Stub Router" flag.
The M, O, H, Prf, P, and R flags are as defined in [RFC5175].
4. Router Advertisement Transmission
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 sets the M and O flags in outgoing RAs is
specified in [I-D.ietf-snac-simple].
5. IANA Considerations
IANA is requested to allocate a flag from the "IPv6 ND Router
Advertisement flags" registry of [RFC5175], as specified below:
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+---------------+----------------------+---------------+
| RA Option Bit | Description | Reference |
+---------------+----------------------+---------------+
| 6 | S - Stub Router Flag | This Document |
+---------------+----------------------+---------------+
Table 1
6. Security Considerations
This protocol shares the security issues of NDP that are documented
in the "Security Considerations" section of [RFC4861].
7. Normative References
[I-D.ietf-snac-simple]
Lemon, T. and J. Hui, "Automatically Connecting Stub
Networks to Unmanaged Infrastructure", Work in Progress,
Internet-Draft, draft-ietf-snac-simple-03, 30 January
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
snac-simple-03>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4193] Hinden, R. and B. Haberman, "Unique Local IPv6 Unicast
Addresses", RFC 4193, DOI 10.17487/RFC4193, October 2005,
<https://www.rfc-editor.org/info/rfc4193>.
[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>.
[RFC5175] Haberman, B., Ed. and R. Hinden, "IPv6 Router
Advertisement Flags Option", RFC 5175,
DOI 10.17487/RFC5175, March 2008,
<https://www.rfc-editor.org/info/rfc5175>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Author's Address
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Jonathan Hui
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 940432
United States of America
Email: jonhui@google.com
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