802.15.4 Informational Element encapsulation of ICMPv6 Router Advertisements
draft-richardson-6lo-ra-in-ie-00

Abstract

In TSCH mode of 802.15.4, as described by [I-D.ietf-6tisch-minimal], opportunities for broadcasts are limited to specific times and specific channels. An enhanced beacon must be broadcast periodically by every router to keep all nodes in sync. This document provides a mechanism by which other small ICMPv6 packets, such as Router Advertisements may be carried within the Enhanced Beacon, providing standard IPv6 router/host protocol.

Status of This Memo

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This Internet-Draft will expire on April 21, 2017.

Copyright Notice

Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 1.1. Terminology
• 1.2. Layer-2 Synchronization
• 1.3. Layer-3 synchronization IPv6 Router solicitations and advertisements
• 2. Protocol Definition
• 2.1. Protocol Example
• 3. Security Considerations
• 4. IANA Considerations
• 5. References
• 5.1. Normative References
• 5.2. Informative References
• Appendix A. appendix
• Author's Address

1. Introduction

[I-D.ietf-6tisch-architecture] describes the use of the time-slotted channel hopping (TSCH) mode of [ieee802154]. As further details in [I-D.ietf-6tisch-minimal], an Extended Beacon is transmitted during a slot designated a broadcast slot.

EDNOTE: Explain why broadcasts are rare, and why we need them. What the Enhanced Beacon is, and what Information Elements are, and how the IETF has a subtype for that area. Explain what kind of things could be placed in Information Elements, how big they could be, and how they could be compressed.

1.1. Terminology

In this document, the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] and indicate requirement levels for compliant STuPiD implementations.

1.2. Layer-2 Synchronization

As explained in section 6 of [I-D.ietf-6tisch-minimal], the Extended Beacon has a number of purposes: synchronization of ASN and Join Metric, timeslot template identifier, the channel hopping sequence identifier, TSCH SlotFrame and Link IE.

The Extended Beacon is used by operating nodes to correct drift to their clock, by nodes on medium length sleeps to resynchronize their ASN, by nodes that have slept through a network rekey to rediscover the network, and by new Joining Nodes (pledges) to learn about the existance of the network.

There are a limited number of timeslots designated as a broadcast slot by each router. These slots are rare, and with 10ms slots, with a slot-frame length of 100, there may be only 1 slot/s for the beacon.

1.3. Layer-3 synchronization IPv6 Router solicitations and advertisements

At layer 3, [RFC2461] defines a mechanism by which nodes learn about routers by listening for multicasted Router Advertisements (RA). If no RA is heard within a set time, then a Router Solicitation (RS) may be multicast, to which an RA will be received, usually unicast.

Although [RFC6775] reduces the amount of multicast necessary to do address resolution via Neighbor Solicitation messages, it still requires multicast of either RAs or RS. This is an expensive operation for two reasons: there are few multicast timeslots for unsolicited RAs; if a pledge node does not hear an RA, and decides to send a RS (consuming a broadcast aloha slot with unencrypted traffic), many unicast RS may be sent in response.

This is a particularly acute issue for the join process for the following reasons:

1. use of a multicast slot by even a non-malicious unauthenticated node for a Router Solicitation may overwhelm that time slot.
2. it may require many seconds of on-time before a new pledge hears a Router Soliciation that it can use.
3. a new pledge may listen to many Enhanced Beacons before it can pick an appropriate network and/or closest Join Assistant to attach to. If it must listen for a RS as well as find the Enhanced Beacon, then the process may take a very long time.

2. Protocol Definition

[I-D.kivinen-802-15-ie] creates a registry for new IETF IE subtypes. This document allocates a new subtype TBD-XXX.

The base IE subtype structure is as follows. As explained in [I-D.kivinen-802-15-ie] the length of the Sub-Type Content can be calculated.

                     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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   TBD-XXX     |       6LoRH encoded structure                 |
+-+-+-+-+-+-+-+-+                                               |
~                       Sub-Type Content                        ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Inside the Sub-Type content should be placed compressed packets according to [RFC6282] (as updated by [I-D.ietf-6lo-dispatch-iana-registry].

2.1. Protocol Example

Typically a Router Advertisement will be placed inside the Sub-Type. The entire structure typically looks like:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver  6 | TC = 0        |           Flow Label = 0              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|         Payload Length        |  NH = 58      | Hop Lmt = 1   |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
+                                                               +
|                                                               |
+                         Source Address                        +
|                           fe80::LL                            |
+                                                               +
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
+                                                               +
|                                                               |
+                      Destination Address                      +
|                           fe02::1                             |
+                                                               +
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Type = 134   |  Code = 0     |          Checksum             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HL = 0        |0|0|  Reserved |  Router lifetime = 9000       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Reachable Time   = 0  XXX             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Retrans Timer   = 0  XXX             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1      | Len = 10      |    EUI-64 of router           |
+-+-+-+-+-+-+-+-+-+-+-+---------+                               +
|                    EUI-64 of router                           |
+                               +---------------+---------------+
| EUI-64 of router              | Type = TBD-YYY|  Len = 18     |
+-------------------------------+-------------------------------+
|                             DODAGID                           |
+                                                               |
|                                                               |
+                                                               |
|                                                               |
+                                                               |
|                                                               |
+---------------------------------------------------------------+

When compressed by [RFC6282], this becomes:

+---------------------------------------------------------------+
| 0 | 1 | 1 |TF= 11 |NH |HLIM=01|CID|SAC|  SAM  | M |DAC|  DAM  | 0
+   |   |   |       | 0 |       | 0 | 0 | 0   1 + 1 + 0 + 1   1 +
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| NH = 0x58                     |   dstXX = 0x01                | 4
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Type = 134   |  Code = 0     |          Checksum             | 8
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| HL = 0        |0|0|  Reserved |  Router lifetime = 9000       | 12
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Reachable Time   = 0  XXX             | 16
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          Retrans Timer   = 0  XXX             | 20
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 1      | Len = 10      |    EUI-64 of router           | 24
+-+-+-+-+-+-+-+-+-+-+-+---------+                               +
|                    EUI-64 of router                           | 28
+                               +---------------+---------------+
| EUI-64 of router              | Type = TBD-YYY|  Len = 18     | 32
+-------------------------------+-------------------------------+
|                             DODAGID                           | 36
+                                                               |
|                                                               | 40
+                                                               |
|                                                               | 44
+                                                               |
|                                                               | 48
+---------------------------------------------------------------+

The total number of bytes needed is 56 bytes.

3. Security Considerations

TBD.

4. IANA Considerations

Allocate a new number TBD-XXX from Registry IETF IE Sub-type ID. This entry should be called 6LoRH-in-IE.

Allocate a new number TBD-YYY from Neighbor Discovery Option Types (RFC2461) with the name "Constrained Network Identification".

5. References

5.1. Normative References

5.2. Informative References

Appendix A. appendix

insert appendix here

Author's Address