6lo P. Thubert, Ed.
Internet-Draft Cisco
Intended status: Standards Track C. Bormann
Expires: July 18, 2016 Uni Bremen TZI
L. Toutain
IMT-TELECOM Bretagne
R. Cragie
ARM
January 15, 2016
6LoWPAN Routing Header And Paging Dispatches
draft-ietf-6lo-routing-dispatch-03
Abstract
This specification introduces a new 6LoWPAN dispatch type for use in
6LoWPAN Route-Over topologies, that initially covers the needs of RPL
(RFC6550) data packets compression. Using this dispatch type, 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.
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This Internet-Draft will expire on July 18, 2016.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Using the Page Dispatch . . . . . . . . . . . . . . . . . . . 5
3.1. New Routing Header Dispatch (6LoRH) . . . . . . . . . . . 6
3.2. Placement Of The 6LoRH . . . . . . . . . . . . . . . . . 6
4. 6LoWPAN Routing Header General Format . . . . . . . . . . . . 6
4.1. Elective Format . . . . . . . . . . . . . . . . . . . . . 7
4.2. Critical Format . . . . . . . . . . . . . . . . . . . . . 7
5. The Routing Header Type 3 (RH3) 6LoRH Header . . . . . . . . 8
6. The RPL Packet Information 6LoRH . . . . . . . . . . . . . . 10
6.1. Compressing the RPLInstanceID . . . . . . . . . . . . . . 11
6.2. Compressing the SenderRank . . . . . . . . . . . . . . . 11
6.3. The Overall RPI-6LoRH encoding . . . . . . . . . . . . . 12
7. The IP-in-IP 6LoRH Header . . . . . . . . . . . . . . . . . . 14
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9.1. Reserving Space in 6LoWPAN Dispatch Page 1 . . . . . . . 15
9.2. Nex 6LoWPAN Routing Header Type Registry . . . . . . . . 16
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
11.1. Normative References . . . . . . . . . . . . . . . . . . 16
11.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving energy, a very constrained resource in most cases.
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
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
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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 802.15.4 [IEEE802154] is limited to 127
bytes per frame. The need to compress IPv6 packets over IEEE
802.15.4 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 flows outside the LLN.
When to use RFC 6553, 6554 and IPv6-in-IPv6
[I-D.robles-roll-useofrplinfo] details different cases where RFC
6553, RFC 6554 and IPv6-in-IPv6 encapsulation is required to set the
bases to help defining the compression of RPL routing information in
LLN environments.
When using [RFC6282] the outer IP header of an IP-in-IP encapsulation
may be compressed down to 2 octets in stateless compression and down
to 3 octets in stateful compression when context information must be
added.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
| 0 | 1 | 1 | TF |NH | HLIM |CID|SAC| SAM | M |DAC| DAM |
+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 1: LOWPAN_IPHC base Encoding (RFC6282).
The Stateless Compression of an IPv6 addresses can only happen if the
IPv6 address can de deduced from the MAC addresses, meaning that the
IP end point is also the MAC-layer endpoint. This is generally not
the case in a RPL network which is generally a multi-hop route-over
(i.e., operated at Layer-3) network. A better compression, which
does not involve variable compressions depending on the hop in the
mesh, can be achieved based on the fact that the outer encapsulation
is usually between the source (or destination) of the inner packet
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and the root. Also, the inner IP header can only be compressed by
[RFC6282] if all the fields preceding it are also compressed. This
specification makes the inner IP header the first header to be
compressed by [RFC6282], and keeps the inner packet encoded the same
way whether it is encapsulated or not, thus preserving existing
implementations.
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, while 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 inserted
in packets entering the domain and be removed from packets that leave
the domain. In both cases, this operation implies an IP-in-IP
encapsulation.
------+--------- ^
| 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 2: 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
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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 in order to insert
the RH3.
6TiSCH [I-D.ietf-6tisch-architecture] specifies the operation of IPv6
over the TimeSlotted Channel Hopping [RFC7554] (TSCH) mode of
operation of IEEE 802.15.4. The architecture requires the use of
both RPL and the 6lo adaptation layer over IEEE 802.15.4. Because it
inherits the constraints on frame size from the MAC layer, 6TiSCH
cannot afford to allocate 8 bytes per packet on the RPI. Hence the
requirement for 6LoWPAN header compression of the RPI.
An extensible compression technique is required that simplifies IP-
in-IP encapsulation when it is needed, and optimally compresses
existing routing artifacts found in RPL LLNs.
This specification extends the 6lo adaptation layer framework
([RFC4944],[RFC6282]) so as to carry routing information for route-
over networks based on RPL. The 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. Using the Page Dispatch
The6LoWPAN Paging Dispatch [I-D.ietf-6lo-paging-dispatch]
specification extends the 6lo adaptation layer framework ([RFC4944],
[RFC6282]) by introducing a concept of "context" in the 6LoWPAN
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parser, a context being identified by a Page number. The
specification defines 16 Pages.
This draft operates within Page 1, which is indicated by a Dispatch
Value of binary 11110001.
3.1. 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 RPI 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 use.
This specification uses the bit pattern 10xxxxxx in Page 1 for the
new 6LoRH Dispatch. Section 4 describes how RPL artifacts in data
packets can be compressed as 6LoRH headers.
3.2. Placement Of The 6LoRH
In a zone of a packet where Page 1 is active (i.e., once a Page 1
Paging Dispatch is parsed and no subsequent Paging Dispatch has been
parsed, the parsing of the packet MUST follow this specification if
the 6LoRH Bit Pattern Section 3.1 is found.
With this specification, the 6LoRH Dispatch is only defined in Page
1, so it MUST be placed in the packet in a zone where the Page 1
context is active.
One or more 6LoRH header(s) MAY be placed in a 6LoWPAN packet. A
6LoRH header MUST always be placed before the LOWPAN_IPHC as defined
in 6LoWPAN Header Compression [RFC6282].
Because a 6LoRH header requires a Page 1 context, it MUST always be
placed after any Fragmentation Header and/or Mesh Header [RFC4944].
4. 6LoWPAN Routing Header General Format
The 6LoRH reuses in Page 1 the Dispatch Value Bit Pattern of
10xxxxxx.
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
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4.1. Elective Format
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 enables a node to skip a 6LoRHE header that it does
not support and/or cannot parse, for instance if the Type is not
recognized.
Type:
Type of the 6LoRHE
4.2. Critical Format
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: The situation where a node receives a message with a Critical
6LoWPAN Routing Header that it does not understand is a critical
administrative error whereby the wrong device is placed in a network.
It makes no sense to overburden the constrained device with code that
would send an ICMP error to the source. Rather, it is expected that
the device will raise some management alert indicating that it cannot
operate in this network for that reason. As a result, there is no
provision for the exchange of error messages for this situation, so
it should be avoided by judicious use of administrative control and/
or capability indications by the device manufacturer.
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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| 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
5. The Routing Header Type 3 (RH3) 6LoRH Header
The Routing Header type 3 (RH3) 6LoRH (RH3-6LoRH) header 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 are expected to support this specification. If a non-RPL
router receives a packet with a RH3-6LoRH, this means that there was
a routing error and the packet should be dropped so the Type cannot
be ignored.
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. The unit (as a number
of bytes) in which the Size is expressed depends on the Type as
described in Figure 6:
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+-----------+-----------+
| 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 header, 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 elements can be
employed.)
The Next Hop is indicated in the first entry of the first RH3-6LoRH
header. Upon reception, the router checks whether the address
indicated as Next Hop is one of its own addresses, which MUST be the
case in a strict source-routing environment. In that case, the entry
is removed from the RH3-6LoRH header and the Size is decremented. If
that makes the Size zero, the whole RH3-6LoRH header is removed. If
there are no more RH3-6LoRH headers, the processing node is the last
router on the path, which may or may not be collocated with the final
destination.
The last hop in the last RH3-6LoRH is the last router on the way to
the destination in the LLN. In a classical RPL network, all nodes
are routers so the last hop is effectively the destination as well,
but in the general case, even when there is a RH3-6LoRH header
present, the address of the final destination is always indicated in
the LoWPAN_IPHC [RFC6282].
If some bits of the first address in the RH3-6LoRH header can be
derived from the final destination in the LoWPAN_IPHC, then that
address may be compressed; otherwise it is expressed as a full IPv6
address of 128 bits. Next addresses only need to express the delta
from the previous address.
All addresses in a given RH3-6LoRH header are compressed in an
identical fashion, down to using the identical number of bytes per
address. In order to get different degrees of compression, multiple
consecutive RH3-6LoRH headers MUST be used
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6. The RPL Packet Information 6LoRH
[RFC6550], Section 11.2, specifies the RPL Packet Information (RPI)
as a set of fields that are placed by RPL routers in 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
a specialized Objective Function such as [RFC6552], indicates the
Rank of the sender and is modified at each hop. The SenderRank field
is used 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, which must
be placed in a Hop-by-Hop header that consumes two additional octets
for a total of eight octets. To limit the header's range to just 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-byte overhead is detrimental to 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 leads to
even more energy expenditure and issues discussed in 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.
For that reason, this specification defines an IP-in-IP-6LoRH header
in Section 7, but it must be noted that removal of a 6LoRH header
does not require manipulation of the packet in the LOWPAN_IPHC, and
thus, if the source address in the LOWPAN_IPHC is the node that
inserted the IP-in-IP-6LoRH header then this situation alone does not
mandate an IP-in-IP-6LoRH header.
Note: A typical packet in RPL non-storing mode going down the RPL
graph requires an IP-in-IP encapsulation of the RH3, whereas the RPI
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is usually (and quite illegally) omitted, unless it is important to
indicate the RPLInstanceID. To match this structure, an optimized
IP-in-IP 6LoRH header is defined in Section 7.
As a result, a RPL packet may bear only an RPI-6LoRH header and no
IP-in-IP-6LoRH header. In that case, the source and destination of
the packet are specified by 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 header, which is
a Critical 6LoWPAN Routing Header that is designed to transport the
RPI in 6LoWPAN LLNs.
6.1. Compressing the RPLInstanceID
RPL Instances are discussed in [RFC6550], Section 5. A number of
simple use cases do not require more than one instance, and in such
cases, 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.
6.2. 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
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as 256 and in [RFC6552] that defaults MinHopRankIncrease to
DEFAULT_MIN_HOP_RANK_INCREASE.
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.
6.3. The Overall RPI-6LoRH encoding
The RPI-6LoRH header provides a compressed form for the RPL RPI.
Routers that need to forward a packet with a RPI-6LoRH header are
expected to be RPL routers that support this specification. If a
non-RPL router receives a packet with a RPI-6LoRH header, there was a
routing error and the packet should be dropped. Thus the Type field
MUST NOT be ignored.
Since the I flag is not set, the TSE field does not need to be a
length expressed in bytes. In that case the field is fully reused
for control bits that encode the O, R and F flags from the RPI, as
well as the I and K flags that indicate the compression format.
The Type for the RPI-6LoRH is 5.
The RPI-6LoRH header 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 two
bytes. The I and K flags in the RPI-6LoRH header indicate whether
the RPLInstanceID is elided and/or the SenderRank is compressed.
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 are 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.
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K bit: If it is set, the SenderRank is compressed into one octet,
with the least significant octet elided. If it is not set, the
SenderRank, is fully inlined as two 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.
7. The IP-in-IP 6LoRH Header
The IP-in-IP 6LoRH (IP-in-IP-6LoRH) header 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 IP-in-IP 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 the last router prior to
Destination to remove a field such as the RPI, but this can be done
in the compressed form by removing the RPI-6LoRH, so an IP-in-IP-
6LoRH encapsulation is not required for that sole purpose.
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 13: The IP-in-IP-6LoRH.
The Length of an IP-in-IP-6LoRH header 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 IP-in-IP-6LoRH header 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.
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If the Length of an IP-in-IP-6LoRH header is greater 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 header 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 headers 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 a 6LoRH header 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.
8. 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 is believed to not create an opening for a
new threat when compared to [RFC6550], [RFC6553] and [RFC6554].
9. IANA Considerations
9.1. Reserving Space in 6LoWPAN Dispatch Page 1
This specification reserves Dispatch Value Bit Patterns within the
6LoWPAN Dispatch Page 1 as follows:
101xxxxx: for Elective 6LoWPAN Routing Headers
100xxxxx: for Critical 6LoWPAN Routing Headers.
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9.2. Nex 6LoWPAN Routing Header Type Registry
This document creates an IANA registry for the 6LoWPAN Routing Header
Type, and assigns the following values:
0..4: RH3-6LoRH [RFCthis]
5: RPI-6LoRH [RFCthis]
6: IP-in-IP-6LoRH [RFCthis]
10. Acknowledgments
The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei
Chang, 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.
11. References
11.1. Normative References
[I-D.ietf-6lo-paging-dispatch]
Thubert, P., "6LoWPAN Paging Dispatch", draft-ietf-6lo-
paging-dispatch-01 (work in progress), January 2016.
[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>.
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[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>.
[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>.
11.2. Informative References
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[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-09 (work
in progress), November 2015.
[I-D.robles-roll-useofrplinfo]
Robles, I., Richardson, M., and P. Thubert, "When to use
RFC 6553, 6554 and IPv6-in-IPv6", draft-robles-roll-
useofrplinfo-02 (work in progress), October 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.
[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>.
[RFC7554] Watteyne, T., Ed., Palattella, M., and L. Grieco, "Using
IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the
Internet of Things (IoT): Problem Statement", RFC 7554,
DOI 10.17487/RFC7554, May 2015,
<http://www.rfc-editor.org/info/rfc7554>.
Appendix A. Examples
The example in Figure 14 illustrates the 6LoRH compression of a
classical packet in Storing Mode in all directions, as well as in
non-Storing mode for a packet going up the DODAG following the
default route to the root. In this particular example, a
fragmentation process takes place per [RFC4944], and the fragment
headers must be placed in Page 0 before switching to Page 1:
+- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+...
|Frag type|Frag hdr |11110001|IP-in-IP| RPI | RFC 6282 Dispatch
|RFC 4944 |RFC 4944 | Page 1 | 6LoRH | 6LoRH | + LOWPAN_IPHC
+- ... -+- ... -+-+ ... -+-+ ... -+- ... +-+-+-+-+-+-+-+-+-+-+...
<- RFC 6282 ->
No RPL artifact
Figure 14: Example Compressed Packet with RPI.
The example illustrated in Figure 15 is a classical packet in non-
Storing mode for a packet going down the DODAG following a source
routed path from the root; in this particular example, addresses in
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the DODAG are assigned to share a same /112 prefix, for instance
taken from a /64 subnet with the first 6 octets of the suffix set to
a constant such as all zeroes. In that case, all addresses but the
first can be compressed to 2 octets, which means that there will be 2
RH3_6LoRH headers, one to store the first complete address and the
one to store the sequence of addresses compressed to 2 octets (in
this example, 3 of them):
+- ... -+- ... -+-+-+- ... -+-+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+...
|11110001|IP-in-IP| RH3(128bits)| RH3(3*16bits)| RFC 6282 Dispatch
|Page 1 | 6LoRH | 6LoRH | 6LoRH | + LOWPAN_IPHC
+- ... -+- ... +-+-+-+- ... -+-+-+-+-+ ... -+-+-+-+-+-+-+-+-+-+-+...
<- RFC 6282 ->
No RPL artifact
Figure 15: Example Compressed Packet with RH3.
Note: the RPI is not represented since most implementations actually
refrain from placing it in a source routed packet though [RFC6550]
generally expects it.
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems
Building D - Regus
45 Allee des Ormes
BP1200
MOUGINS - Sophia Antipolis 06254
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
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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
Robert Cragie
ARM Ltd.
110 Fulbourn Road
Cambridge CB1 9NJ
UK
Email: robert.cragie@gridmerge.com
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