6lo P. Thubert, Ed.
Internet-Draft Cisco
Updates: 4944 (if approved) C. Bormann
Intended status: Standards Track Uni Bremen TZI
Expires: February 7, 2016 L. Toutain
IMT-TELECOM Bretagne
R. Cragie
ARM
August 06, 2015
A Routing Header Dispatch for 6LoWPAN
draft-thubert-6lo-routing-dispatch-06
Abstract
This specification introduces a new context switch mechanism for
6LoWPAN compression, expressed in terms of Pages. A new 6LoWPAN
dispatch type is proposed in a new Page 1 for use in 6LoWPAN Route-
Over topologies, that initially covers the needs of RPL (RFC6550)
data packets compression. This specification defines a method to
compress RPL Option (RFC6553) information and Routing Header type 3
(RFC6554), an efficient IP-in-IP technique and is extensible for more
applications.
Status of This Memo
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 http://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 February 7, 2016.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Updating RFC 4944 . . . . . . . . . . . . . . . . . . . . . . 5
3.1. New Page1 Dispatch . . . . . . . . . . . . . . . . . . . 6
3.2. New Routing Header Dispatch (6LoRH) . . . . . . . . . . . 6
3.3. Sur-Compression Mechanisms . . . . . . . . . . . . . . . 6
4. Placement Of The New Dispatch Types . . . . . . . . . . . . . 7
4.1. Placement Of The Page1 Dispatch . . . . . . . . . . . . . 7
4.2. Placement Of The 6LoRH . . . . . . . . . . . . . . . . . 7
5. 6LoWPAN Routing Header General Format . . . . . . . . . . . . 8
5.1. Elective Format . . . . . . . . . . . . . . . . . . . . . 8
5.2. Critical Format . . . . . . . . . . . . . . . . . . . . . 9
6. The Routing Header Type 3 (RH3) 6LoRH . . . . . . . . . . . . 9
7. The RPL Packet Information 6LoRH . . . . . . . . . . . . . . 11
7.1. Compressing the RPLInstanceID . . . . . . . . . . . . . . 12
7.2. Compressing the SenderRank . . . . . . . . . . . . . . . 12
7.3. The Overall RPI-6LoRH encoding . . . . . . . . . . . . . 13
8. The IP-in-IP 6LoRH . . . . . . . . . . . . . . . . . . . . . 15
9. The BIER 6LoRH . . . . . . . . . . . . . . . . . . . . . . . 17
10. Security Considerations . . . . . . . . . . . . . . . . . . . 18
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 19
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
13.1. Normative References . . . . . . . . . . . . . . . . . . 19
13.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving energy, which is the most constrained resource of
all. The other constraints, such as the memory capacity and the duty
cycling of the LLN devices, derive from that primary concern. Energy
is often available from primary batteries that are expected to last
for years, or is scavenged from the environment in very limited
quantities. Any protocol that is intended for use in LLNs must be
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designed with the primary concern of saving energy as a strict
requirement.
Controlling the amount of data transmission is one possible venue to
save energy. In a number of LLN standards, the frame size is limited
to much smaller values than the IPv6 maximum transmission unit (MTU)
of 1280 bytes. In particular, an LLN that relies on the classical
Physical Layer (PHY) of IEEE 802.14.5 [IEEE802154] is limited to 127
bytes per frame. The need to compress IPv6 packets over IEEE
802.14.5 led to the 6LoWPAN Header Compression [RFC6282] work
(6LoWPAN-HC).
Innovative Route-over techniques have been and are still being
developed for routing inside a LLN. In a general fashion, such
techniques require additional information in the packet to provide
loop prevention and to indicate information such as flow
identification, source routing information, etc.
For reasons such as security and the capability to send ICMP errors
back to the source, an original packet must not be tampered with, and
any information that must be inserted in or removed from an IPv6
packet must be placed in an extra IP-in-IP encapsulation. This is
the case when the additional routing information is inserted by a
router on the path of a packet, for instance a mesh root, as opposed
to the source node. This is also the case when some routing
information must be removed from a packet that will flow outside the
LLN.
As an example, the Routing Protocol for Low Power and Lossy Networks
[RFC6550] (RPL) is designed to optimize the routing operations in
constrained LLNs. As part of this optimization, RPL requires the
addition of RPL Packet Information (RPI) in every packet, as defined
in Section 11.2 of [RFC6550].
The RPL Option for Carrying RPL Information in Data-Plane Datagrams
[RFC6553] specification indicates how the RPI can be placed in a RPL
Option for use in an IPv6 Hop-by-Hop header. This representation
demands a total of 8 bytes when in most cases the actual RPI payload
requires only 19 bits. Since the Hop-by-Hop header must not flow
outside of the RPL domain, it must be removed from packets that leave
the domain, and be inserted in packets entering the domain. In both
cases, this operation implies an IP-in-IP encapsulation.
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------+--------- ^
| Internet |
| | Native IPv6
+-----+ |
| | Border Router (RPL Root) ^ | ^
| | | | |
+-----+ | | | IPv6 in
| | | | IPv6
o o o o | | | + RPI
o o o o o o o o o | | | or RH3
o o o o o o o o o o | | |
o o o o o o o o o | | |
o o o o o o o o v v v
o o o o
LLN
Figure 1: IP-in-IP Encapsulation within the LLN
Additionally, in the case of the Non-Storing Mode of Operation (MOP),
RPL requires a Routing Header type 3 (RH3) as defined in the IPv6
Routing Header for Source Routes with RPL [RFC6554] specification,
for all packets that are routed down a RPL graph. With Non-Storing
RPL, even if the source is a node in the same LLN, the packet must
first reach up the graph to the root so that the root can insert the
RH3 to go down the graph. In any fashion, whether the packet was
originated in a node in the LLN or outside the LLN, and regardless of
whether the packet stays within the LLN or not, as long as the source
of the packet is not the root itself, the source-routing operation
also implies an IP-in-IP encapsulation at the root to insert the RH3.
6TiSCH [I-D.ietf-6tisch-architecture] specifies the operation of IPv6
over the TimeSlotted Channel Hopping [I-D.ietf-6tisch-tsch] (TSCH)
mode of operation of IEEE 802.14.5. The architecture requires the
use of both RPL and the 6lo adaptation layer framework ([RFC4944],
[RFC6282]) over IEEE 802.14.5. Because it inherits the constraints
on the frame size from the MAC layer, 6TiSCH cannot afford to spend 8
bytes per packet on the RPI. Hence the requirement for a 6LoWPAN
header compression of the RPI.
The type of information that needs to be present in a packet inside
the LLN but not outside of the LLN varies with the routing operation,
but there is overall a need for an extensible compression technique
that would simplify the IP-in-IP encapsulation, when needed, and
optimally compress existing routing artifacts found in LLNs.
This specification extends 6LoWPAN [RFC4944] and in particular reuses
the Mesh Header formats that are defined for the Mesh-under use cases
so as to carry routing information for Route-over use cases. The
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specification includes the formats necessary for RPL and is
extensible for additional formats.
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
[RFC2119].
The Terminology used in this document is consistent with and
incorporates that described in `Terminology in Low power And Lossy
Networks' [RFC7102] and [RFC6550].
The terms Route-over and Mesh-under are defined in [RFC6775].
Other terms in use in LLNs are found in [RFC7228].
The term "byte" is used in its now customary sense as a synonym for
"octet".
3. Updating RFC 4944
This draft adapts 6LoWPAN while maintaining backward compatibility
with IPv6 over IEEE 802.15.4 [RFC4944] by introducing a concept of
context in the 6LoWPAN parser, a context being identified by a Page
number, and defines 16 Pages.
Pages are delimited in a 6LoWPAN packet by a dispatch value that
indicates the next current Page. The Page number is encoded in a
Dispatch Value Bit Pattern of 1111xxxx where xxxx is the Page number,
0 to 15, as follows:
0
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|1|1|1|1|Page Nb|
+-+-+-+-+-+-+-+-+
Figure 2: Page encoding
Values of the Dispatch byte defined in [RFC4944] are considered as
belonging to a Page 0 parsing context, which is the default and does
not need to be signaled explicitly at the beginning of a 6LoWPAN
packet. That way, backward compatibility with existing
implementations in ensured.
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Note: This specification does not use the Escape Dispatch, which
extends Page 0 to more values, but rather allocates another Dispatch
Bit Pattern (1111xxxx), in all Pages including Page 0 and Pages
defined in future specifications, to indicate the next parsing
context represented by its Page number.
3.1. New Page1 Dispatch
This draft defines a new Page1 Dispatch with a Dispatch Value of
11110001 that indicates a context switch in the 6LoWPAN parser to a
Page 1.
The Dispatch bits defined in Page 0 by [RFC4944] are free to be
reused in Page 1.
On the other hand, the Dispatch bits defined in Page 0 for the
Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based
Networks [RFC6282] are defined with the same values in Page 1 so
there is no need to switch context back from Page 1 to Page 0 to
address LOWPAN_IPHC and LOWPAN_NHC.
3.2. New Routing Header Dispatch (6LoRH)
This specification introduces a new 6LoWPAN Routing Header (6LoRH) to
carry IPv6 routing information. The 6LoRH may contain source routing
information such as a compressed form of RH3, as well as other sorts
of routing information such as the RPL Packet Information and IP-in-
IP encapsulation.
The 6LoRH is expressed in a 6loWPAN packet as a Type-Length-Value
(TLV) field, which is extensible for future uses. The proposed BIER
bitmap encoding in Section 9 is an example of extension.
Section 5.1 of the [RFC4944] specification defines various Dispatch
Types and Headers, and in particular a Mesh Header that corresponds
to a bit pattern 10xxxxxx (in Page 0).
This specification uses the same bit pattern 10xxxxxx in Page 1 for
the canonical form of 6LoRH Dispatch that is detailed in Section 5
3.3. Sur-Compression Mechanisms
It is expected that virtual-link-specific sur-compression mechanisms
may be applied in the future that merge Dispatch values from multiple
Pages into a single octet, attempting to keep the dispatch bits
settings in their canonical form as much as possible.
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Considering that the Mesh-Under and the Route-Over modes are
generally mutually exclusive, it is expected that the new 6LoRH
Dispatch introduced in this specification can be left in its
canonical form through sur-compression technique.
A dispatch space of equivalent size to the Mesh Header was reserved
in [RFC4944] for external specifications, Not A LowPan (NALP), hoping
that such specification could coexist harmlessly on a same network as
a early 6LoWPAN.
A sur-compression technique may alternatively use the NALP space for
6LoRH, in which case bit patterns represented as 10xxxxxx in this
specification will be mapped directly to 00xxxxxx.
4. Placement Of The New Dispatch Types
4.1. Placement Of The Page1 Dispatch
In a zone of a packet where Page 1 is active, which means once a
Page1 Dispatch is parsed, and as long as no other Page Dispatch is
parsed, the parsing of the packet MUST follow this specification if
the 6LoRH Bit Pattern [Section 5] is found.
Mesh Headers represent Layer-2 information and are processed before
any Layer-3 information that is encoded in Page 1. If a 6LoWPAN
packet requires a Mesh header, the Mesh Header MUST always be placed
in the packet before the first Page1 Dispatch, if any.
For the same reason, Fragments Headers as defined in [RFC4944] MUST
always be placed in the packet before the first Page1 Dispatch, if
any.
It must be noted that the NALP Dispatch Bit Pattern as defined in
[RFC4944] is only defined for the first octet in the packet.
Switching back to Page 0 for NALP inside a 6LoWPAN packet appears
non-sensical.
It results that there is no need so far for restoring the Page 0
parsing context after a context was switched to Page 1, so the value
for the Page0 Dispatch of 11110000 may not actually be seen in
packets following the 6LoWPAN specifications that are available at
the time of this writing.
4.2. Placement Of The 6LoRH
With this specification, the 6LoRH [Section 5] is only defined in
Page 1, so it MUST be placed in the packet in a zone where the Page 1
context is active.
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One or more 6LoRHs MAY be placed in a 6LoWPAN packet and MUST always
be placed before the LOWPAN_IPHC [RFC6282].
A 6LoRH being placed in a Page 1 context, it MUST always be placed
after any Fragmentation Header and/or Mesh Header [RFC4944], even if
a sur-compression mechanism is used that elides the Page Dispatches.
5. 6LoWPAN Routing Header General Format
In its canonical form, the 6LoRH reuses in Page 1 the Dispatch Value
Bit Pattern of 10xxxxxx that is defined in Page 0 for the Mesh Header
in [RFC4944].
The Dispatch Value Bit Pattern is split in two forms of 6LoRH:
Elective (6LoRHE) that may skipped if not understood
Critical (6LoRHC) that may not be ignored
5.1. Elective Format
In its canonical form, the 6LoRHE uses the Dispatch Value Bit Pattern
of 101xxxxx.
A 6LoRHE may be ignored and skipped in parsing.
If it is ignored, the 6LoRHE is forwarded with no change inside the
LLN.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
|1|0|1| Length | Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
<-- Length -->
Figure 3: Elective 6LoWPAN Routing Header
Length:
Length of the 6LoRHE expressed in bytes, excluding the first 2
bytes. This is done to enable a node to skip a 6LoRH that it does
not support and/or cannot parse, for instance if the Type is not
known.
Type:
Type of the 6LoRHE
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5.2. Critical Format
In its canonical form, the 6LoRHC uses the Dispatch Value Bit Pattern
of 100xxxxx.
A node which does not support the 6LoRHC Type MUST silently discard
the packet.
Note: there is no provision for the exchange of error messages; such
a situation should be avoided by judicious use of administrative
control and/or capability indications.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
|1|0|0| TSE | Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
<-- Length implied by Type/TSE -->
Figure 4: Critical 6LoWPAN Routing Header
TSE:
Type Specific Extension. The meaning depends on the Type, which
must be known in all of the nodes. The interpretation of the TSE
depends on the Type field that follows. For instance, it may be
used to transport control bits, the number of elements in an
array, or the length of the remainder of the 6LoRHC expressed in a
unit other than bytes.
Type:
Type of the 6LoRHC
6. The Routing Header Type 3 (RH3) 6LoRH
The Routing Header type 3 (RH3) 6LoRH (RH3-6LoRH) is a Critical
6LoWPAN Routing Header that provides a compressed form for the RH3,
as defined in [RFC6554] for use by RPL routers. Routers that need to
forward a packet with a RH3-6LoRH are expected to be RPL routers and
expected to support this specification. If a non-RPL router receives
a packet with a RPI-6LoRH, this means that there was a routing error
and the packet should be dropped so the Type cannot be ignored.
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0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+
|1|0|0| Size |6LoRH Type 0..4| Hop1 | Hop2 | | HopN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- -+- -+ ... +- -+
Size indicates the number of compressed addresses
Figure 5: The RH3-6LoRH
The values for the RH3-6LoRH Type are an enumeration, 0 to 4. The
form of compression is indicated by the Type as follows:
+-----------+-----------+
| Type | Size Unit |
+-----------+-----------+
| 0 | 1 |
| 1 | 2 |
| 2 | 4 |
| 3 | 8 |
| 4 | 16 |
+-----------+-----------+
Figure 6: The RH3-6LoRH Types
In the case of a RH3-6LoRH, the TSE field is used as a Size, which
encodes the number of hops minus 1; so a Size of 0 means one hop, and
the maximum that can be encoded is 32 hops. (If more than 32 hops
need to be expressed, a sequence of RH3-6LoRH can be employed.)
The next Hop is indicated in the first entry of the first RH3-6LoRH.
Upon reception, the entry is checked whether it refers to the
processing router itself. If it so, the entry is removed from the
RH3-6LoRH and the Size is decremented. If the Size is now zero, the
whole RH3-6LoRH is removed. If there is no more RH3-6LoRH, the
processing node is the last router on the way, which may or may not
be collocated with the final destination.
The last hop in the last RH3-6LoRH is the last router prior to the
destination in the LLN. So even when there is a RH3-6LoRH in the
frame, the address of the final destination is in the LoWPAN_IPHC
[RFC6282].
If some bits of the first address in the RH3-6LoRH can be derived
from the final destination is in the LoWPAN_IPHC, then that address
may be compressed, otherwise is is expressed in full. Next addresses
only need to express the delta from the previous address.
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All addresses in a RH3-6LoRH are compressed in a same fashion, down
to the same number of bytes per address. In order to get different
forms of compression, multiple consecutive RH3-6LoRH must be used.
7. The RPL Packet Information 6LoRH
[RFC6550], Section 11.2, specifies the RPL Packet Information (RPI)
as a set of fields that are to be added to the IP packets for the
purpose of Instance Identification, as well as Loop Avoidance and
Detection.
In particular, the SenderRank, which is the scalar metric computed by
an specialized Objective Function such as [RFC6552], indicates the
Rank of the sender and is modified at each hop. The SenderRank
allows to validate that the packet progresses in the expected
direction, either upwards or downwards, along the DODAG.
RPL defines the RPL Option for Carrying RPL Information in Data-Plane
Datagrams [RFC6553] to transport the RPI, which is carried in an IPv6
Hop-by-Hop Options Header [RFC2460], typically consuming eight bytes
per packet.
With [RFC6553], the RPL option is encoded as six Octets; it must be
placed in a Hop-by-Hop header that consumes two additional octets for
a total of eight. In order to limit its range to the inside the RPL
domain, the Hop-by-Hop header must be added to (or removed from)
packets that cross the border of the RPL domain.
The 8-bytes overhead is detrimental to the LLN operation, in
particular with regards to bandwidth and battery constraints. These
bytes may cause a containing frame to grow above maximum frame size,
leading to Layer 2 or 6LoWPAN [RFC4944] fragmentation, which in turn
cause even more energy spending and issues discussed in the LLN
Fragment Forwarding and Recovery
[I-D.thubert-6lo-forwarding-fragments].
An additional overhead comes from the need, in certain cases, to add
an IP-in-IP encapsulation to carry the Hop-by-Hop header. This is
needed when the router that inserts the Hop-by-Hop header is not the
source of the packet, so that an error can be returned to the router.
This is also the case when a packet originated by a RPL node must be
stripped from the Hop-by-Hop header to be routed outside the RPL
domain.
This specification defines an IPinIP-6LoRH in Section 8 for that
purpose, but it must be noted that stripping a 6LoRH does not require
a manipulation of the packet in the LOWPAN_IPHC, and thus, if the
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source address in the LOWPAN_IPHC is the node that inserted the
IPinIP-6LoRH then this alone does not mandate an IPinIP-6LoRH.
As a result, a RPL packet may bear only a RPI-6LoRH and no IPinIP-
6LoRH. In that case, the source and destination of the packet are
located in the LOWPAN_IPHC.
As with [RFC6553], the fields in the RPI include an 'O', an 'R', and
an 'F' bit, an 8-bit RPLInstanceID (with some internal structure),
and a 16-bit SenderRank.
The remainder of this section defines the RPI-6LoRH, a Critical
6LoWPAN Routing Header that is designed to transport the RPI in
6LoWPAN LLNs.
7.1. Compressing the RPLInstanceID
RPL Instances are discussed in [RFC6550], Section 5. A number of
simple use cases will not require more than one instance, and in such
a case, the instance is expected to be the global Instance 0. A
global RPLInstanceID is encoded in a RPLInstanceID field as follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|0| ID | Global RPLInstanceID in 0..127
+-+-+-+-+-+-+-+-+
Figure 7: RPLInstanceID Field Format for Global Instances
For the particular case of the global Instance 0, the RPLInstanceID
field is all zeros. This specification allows to elide a
RPLInstanceID field that is all zeros, and defines a I flag that,
when set, signals that the field is elided.
7.2. Compressing the SenderRank
The SenderRank is the result of the DAGRank operation on the rank of
the sender; here the DAGRank operation is defined in [RFC6550],
Section 3.5.1, as:
DAGRank(rank) = floor(rank/MinHopRankIncrease)
If MinHopRankIncrease is set to a multiple of 256, the least
significant 8 bits of the SenderRank will be all zeroes; by eliding
those, the SenderRank can be compressed into a single byte. This
idea is used in [RFC6550] by defining DEFAULT_MIN_HOP_RANK_INCREASE
as 256 and in [RFC6552] that defaults MinHopRankIncrease to
DEFAULT_MIN_HOP_RANK_INCREASE.
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This specification allows to encode the SenderRank as either one or
two bytes, and defines a K flag that, when set, signals that a single
byte is used.
7.3. The Overall RPI-6LoRH encoding
The RPI-6LoRH provides a compressed form for the RPL RPI. Routers
that need to forward a packet with a RPI-6LoRH are expected to be RPL
routers and expected to support this specification. If a non-RPL
router receives a packet with a RPI-6LoRH, this means that there was
a routing error and the packet should be dropped so the Type cannot
be ignored.
Since the I flag is not set, the TSE field does not need to be a
length expressed in bytes. The field is fully reused for control
bits so as to encode the O, R and F flags from the RPI, and the I and
K flags that indicate the compression that is taking place.
The Type for the RPI-6LoRH is 5.
The RPI-6LoRH is immediately followed by the RPLInstanceID field,
unless that field is fully elided, and then the SenderRank, which is
either compressed into one byte or fully in-lined as the whole 2
bytes. The I and K flags in the RPI-6LoRH indicate whether the
RPLInstanceID is elided and/or the SenderRank is compressed and
depending on these bits, the Length of the RPI-6LoRH may vary as
described hereafter.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+
|1|0|0|O|R|F|I|K| 6LoRH Type=5 | Compressed fields |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+
Figure 8: The Generic RPI-6LoRH Format
O, R, and F bits:
The O, R, and F bits as defined in [RFC6550], Section 11.2.
I bit:
If it is set, the Instance ID is elided and the RPLInstanceID
is the Global RPLInstanceID 0. If it is not set, the octet
immediately following the type field contains the RPLInstanceID
as specified in [RFC6550] section 5.1.
K bit:
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If it is set, the SenderRank is be compressed into one octet,
and the lowest significant octet is elided. If it is not set,
the SenderRank, is fully inlined as 2 octets.
In Figure 9, the RPLInstanceID is the Global RPLInstanceID 0, and the
MinHopRankIncrease is a multiple of 256 so the least significant byte
is all zeros and can be elided:
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|O|R|F|1|1| 6LoRH Type=5 | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I=1, K=1
Figure 9: The most compressed RPI-6LoRH
In Figure 10, the RPLInstanceID is the Global RPLInstanceID 0, but
both bytes of the SenderRank are significant so it can not be
compressed:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|O|R|F|1|0| 6LoRH Type=5 | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I=1, K=0
Figure 10: Eliding the RPLInstanceID
In Figure 11, the RPLInstanceID is not the Global RPLInstanceID 0,
and the MinHopRankIncrease is a multiple of 256:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|O|R|F|0|1| 6LoRH Type=5 | RPLInstanceID | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
I=0, K=1
Figure 11: Compressing SenderRank
In Figure 12, the RPLInstanceID is not the Global RPLInstanceID 0,
and both bytes of the SenderRank are significant:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|0|0|O|R|F|0|0| 6LoRH Type=5 | RPLInstanceID | Sender-...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
...-Rank |
+-+-+-+-+-+-+-+-+
I=0, K=0
Figure 12: Least compressed form of RPI-6LoRH
A typical packet in RPL non-storing mode going down the RPL graph
requires an IPinIP encapsulating the RH3, whereas the RPI is usually
omitted, unless it is important to indicate the RPLInstanceID. To
match this structure, an optimized IPinIP 6LoRH is defined in
Section 8.
And the types include the setting of I and K as follows:
+-----------+-------+-------+
| Type | I | K |
+-----------+-------+-------+
| 5 | 0 | 0 |
| 6 | 0 | 1 |
| 7 | 1 | 0 |
| 8 | 1 | 1 |
+-----------+-------+-------+
Figure 13: The RPI-6LoRH Types
8. The IP-in-IP 6LoRH
The IP-in-IP 6LoRH (IPinIP-6LoRH) is an Elective 6LoWPAN Routing
Header that provides a compressed form for the encapsulating IPv6
Header in the case of an IP-in-IP encapsulation.
An IPinIP encapsulation is used to insert a field such as a Routing
Header or an RPI at a router that is not the source of the packet.
In order to send an error back regarding the inserted field, the
address of the router that performs the insertion must be provided.
The encapsulation can also enable a router down the path removing a
field such as the RPI, but this can be done in the compressed form by
removing the RPI-6LoRH, so an IPinIP-6LoRH encapsulation is not
required for that sole purpose.
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This field is not critical for routing so the Type can be ignored,
and the TSE field contains the Length in bytes.
0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
|1|0|1| Length | 6LoRH Type 6 | Hop Limit | Encaps. Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
Figure 14: The IPinIP-6LoRH
The Length of an IPinIP-6LoRH is expressed in bytes and MUST be at
least 1, to indicate a Hop Limit (HL), that is decremented at each
hop. When the HL reaches 0, the packet is dropped per [RFC2460]
If the Length of an IPinIP-6LoRH is exactly 1, then the Encapsulator
Address is elided, which means that the Encapsulator is a well-known
router, for instance the root in a RPL graph.
If the Length of an IPinIP-6LoRH is strictly more than 1, then an
Encapsulator Address is placed in a compressed form after the Hop
Limit field. The value of the Length indicates which compression is
performed on the Encapsulator Address. For instance, a Size of 3
indicates that the Encapsulator Address is compressed to 2 bytes.
When it cannot be elided, the destination IP address of the IP-in-IP
header is transported in a RH3-6LoRH as the first address of the
list.
With RPL, the destination address in the IP-in-IP header is
implicitly the root in the RPL graph for packets going upwards, and
the destination address in the IPHC for packets going downwards. If
the implicit value is correct, the destination IP address of the IP-
in-IP encapsulation can be elided.
If the final destination of the packet is a leaf that does not
support this specification, then the chain of 6LoRH must be stripped
by the RPL/6LR router to which the leaf is attached. In that
example, the destination IP address of the IP-in-IP header cannot be
elided.
In the special case where the 6LoRH is used to route 6LoWPAN
fragments, the destination address is not accessible in the IPHC on
all fragments and can be elided only for the first fragment and for
packets going upwards.
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9. The BIER 6LoRH
(Note that the current contents of this section is a proof of concept
only; the details for this encoding need to be developed in parallel
with defining the semantics of a constrained version of BIER.)
The Bit Index Explicit Replication (BIER) 6LoRH (BIER-6LoRH) is an
Elective 6LoWPAN Routing Header that provides a variable-size
container for a BIER Bitmap. BIER can be used to route downwards a
RPL graph towards one or more LLN node, as discussed in the BIER
Architecture [I-D.wijnands-bier-architecture] specification. The
capability to parse the BIER Bitmap is necessary to forward the
packet so the Type cannot be ignored.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+- ... -+
|1|0|0| Size |6LoRHType 15-19| Control Fields | bitmap |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... -+-+-+- ... -+
Figure 15: The BIER-6LoRH
The Type for a BIER-6LoRH indicates the size of words used to build
the bitmap and whether the bitmap is operated as an uncompressed bit-
by-bit mapping, or as a Bloom filter.
In the bit-by-bit case, each bit is mapped in an unequivocal fashion
with a single addressable resource in the network. This may rapidly
lead to large bitmaps, and BIER allows to divide a network into
groups that partition the network so that a given bitmap is locally
significant to one group only. This specification allows to encode a
1-byte Group ID in the BIER-6LoRH Control Fields.
A Bloom Filter can be seen as a compression technique for the bitmap.
A Bloom Filter may generate false positives, which, in the case of
BIER, result in undue forwarding of a packet down a path where no
listener exists.
As an example, the Constrained-Cast [I-D.bergmann-bier-ccast]
specification employs Bloom Filters as a compact representation of a
match or non-match for elements in a large set.
In the case of a Bloom Filter, a number of Hash functions must be run
to obtain a multi-bit signature of an encoded element. This
specification allows to signal an Identifier of the Hash functions
being used to generate a certain bitmap, so as to enable a migration
scenario where Hash functions are renewed. A Hash ID is signaled as
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a 1-byte value, and, depending on the Type, there may be up to 2 or
up to 8 Hash IDs passed in the BIER-6LoRH Control Fields associated
with a Bloom Filter bitmap, as follows:
+-----------+--------------+------------------+-----------+
| Type | encoding | Control Fields | Word Size |
+-----------+--------------+------------------+-----------+
| 15 | bit-by-bit | none | 32 bits |
| 16 | Bloom filter | 2* 1-byte HashID | 32 bits |
| 17 | bit-by-bit | none | 128 bits |
| 18 | Bloom filter | 8* 1-byte HashID | 128 bits |
| 19 | bit-by-bit | 1-byte GroupID | 128 bits |
+-----------+--------------+------------------+-----------+
Figure 16: The BIER-6LoRH Types
In order to address a potentially large number of devices, the bitmap
may grow very large. Yet, the maximum frame size for a given MAC
layer may limit the number of bits that can be dedicated to routing.
The Size indicates the number of words in the bitmap minus one, so a
size of 0 means one word, a Size of 1 means 64 2 words, up to a size
of 31 which means 32 words.
10. Security Considerations
The security considerations of [RFC4944], [RFC6282], and [RFC6553]
apply.
Using a compressed format as opposed to the full in-line format is
logically equivalent and does not create an opening for a new threat
when compared to [RFC6550], [RFC6553] and [RFC6554].
11. IANA Considerations
This document creates a IANA registry for the 6LoWPAN Routing Header
Type, and assigns the following values:
0..4 : RH3-6LoRH [RFCthis]
5 : RPI-6LoRH [RFCthis]
6 : IPinIP-6LoRH [RFCthis]
15..19 : BIER-6LoRH [RFCthis]
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12. Acknowledgments
The authors wish to thank Martin Turon, James Woodyatt, Samita
Chakrabarti, Jonathan Hui, Gabriel Montenegro and Ralph Droms for
constructive reviews to the design in the 6lo Working Group. The
overall discussion involved participants to the 6MAN, 6TiSCH and ROLL
WGs, thank you all. Special thanks to the chairs of the ROLL WG,
Michael Richardson and Ines Robles, and Brian Haberman, Internet Area
A-D, and Adrian Farrel, Routing Area A-D, for driving this complex
effort across Working Groups and Areas.
13. References
13.1. Normative References
[IEEE802154]
IEEE standard for Information Technology, "IEEE std.
802.15.4, Part. 15.4: Wireless Medium Access Control (MAC)
and Physical Layer (PHY) Specifications for Low-Rate
Wireless Personal Area Networks", 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/
RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<http://www.rfc-editor.org/info/rfc4944>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<http://www.rfc-editor.org/info/rfc6282>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550, DOI 10.17487/
RFC6550, March 2012,
<http://www.rfc-editor.org/info/rfc6550>.
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[RFC6552] Thubert, P., Ed., "Objective Function Zero for the Routing
Protocol for Low-Power and Lossy Networks (RPL)", RFC
6552, DOI 10.17487/RFC6552, March 2012,
<http://www.rfc-editor.org/info/rfc6552>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553, DOI
10.17487/RFC6553, March 2012,
<http://www.rfc-editor.org/info/rfc6553>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554, DOI
10.17487/RFC6554, March 2012,
<http://www.rfc-editor.org/info/rfc6554>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <http://www.rfc-editor.org/info/rfc7102>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228, DOI 10.17487/
RFC7228, May 2014,
<http://www.rfc-editor.org/info/rfc7228>.
13.2. Informative References
[I-D.bergmann-bier-ccast]
Bergmann, O., Bormann, C., and S. Gerdes, "Constrained-
Cast: Source-Routed Multicast for RPL", draft-bergmann-
bier-ccast-00 (work in progress), November 2014.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-08 (work
in progress), May 2015.
[I-D.ietf-6tisch-tsch]
Watteyne, T., Palattella, M., and L. Grieco, "Using
IEEE802.15.4e TSCH in an IoT context: Overview, Problem
Statement and Goals", draft-ietf-6tisch-tsch-06 (work in
progress), March 2015.
[I-D.thubert-6lo-forwarding-fragments]
Thubert, P. and J. Hui, "LLN Fragment Forwarding and
Recovery", draft-thubert-6lo-forwarding-fragments-02 (work
in progress), November 2014.
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[I-D.wijnands-bier-architecture]
Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
S. Aldrin, "Multicast using Bit Index Explicit
Replication", draft-wijnands-bier-architecture-05 (work in
progress), March 2015.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC
6775, DOI 10.17487/RFC6775, November 2012,
<http://www.rfc-editor.org/info/rfc6775>.
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems
Village d'Entreprises Green Side
400, Avenue de Roumanille
Batiment T3
Biot - Sophia Antipolis 06410
FRANCE
Phone: +33 4 97 23 26 34
Email: pthubert@cisco.com
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
Laurent Toutain
Institut MINES TELECOM; TELECOM Bretagne
2 rue de la Chataigneraie
CS 17607
Cesson-Sevigne Cedex 35576
France
Email: Laurent.Toutain@telecom-bretagne.eu
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Robert Cragie
ARM Ltd.
110 Fulbourn Road
Cambridge CB1 9NJ
UK
Email: robert.cragie@gridmerge.com
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