Internet DRAFT - draft-thubert-6lo-bier-dispatch
draft-thubert-6lo-bier-dispatch
6lo P. Thubert, Ed.
Internet-Draft Cisco
Intended status: Standards Track Z. Brodard
Expires: August 1, 2019 Ecole Polytechnique
H. Jiang
G. Texier
Telecom Bretagne
January 28, 2019
A 6loRH for BitStrings
draft-thubert-6lo-bier-dispatch-06
Abstract
This specification extends the 6LoWPAN Routing Header to signal
BitStrings such as utilized in Bit Index Explicit Replication and its
Traffic Engineering variant.
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 August 1, 2019.
Copyright Notice
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3
4. The BIER-6LoRH encoding . . . . . . . . . . . . . . . . . . . 4
4.1. The Bit-by-bit BitStrings . . . . . . . . . . . . . . . . 4
4.2. The Enumeration BitStrings . . . . . . . . . . . . . . . 5
4.3. Bloom Filters . . . . . . . . . . . . . . . . . . . . . . 5
4.4. Types of BIER-6LoRH header . . . . . . . . . . . . . . . 6
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
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.
The 6LoWPAN Routing Header (6LoRH) [RFC8025] [RFC8138] is such a
technique, that extends the 6lo adaptation layer framework [RFC4944],
[RFC6282] so as to carry routing information for Route-over use
cases. The original specification includes the formats necessary for
RPL such as the Source Route Header (SRH) and is intended to be
extended for additional routing artifacts.
The Bit Index Explicit Replication (BIER), as introduced in the BIER
Architecture [RFC8279], can be used as an alternate artifact to route
multicast as well as unicast traffic. The Traffic Engineering for
Bit Index Explicit Replication [I-D.eckert-bier-te-arch] (BIER-TE)
adds support for traffic engineering by explicit hop-by-hop
forwarding and loose hop forwarding of packets along a unicast route.
This specification provides additional formats for the 6LoRH
compression to carry BitStrings such as used for Bit Index Explicit
Replication and its Traffic Engineering variant (BIER and BIER-TE,
respectively).
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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
[RFC2119].
The Terminology used in this document is consistent with and
incorporates that described in Terms Used in Routing for Low-Power
and Lossy Networks (LLNs). [RFC7102].
Other terms in use in LLNs are found in Terminology for Constrained-
Node Networks [RFC7228].
The term "byte" is used in its now customary sense as a synonym for
"octet".
"RPL", "RPL Packet Information" (RPI) and "RPL Instance" are defined
in the RPL: IPv6 Routing Protocol for Low-Power and Lossy Networks
[RFC6550] specification.
The terms Bit-Forwarding Egress Routers (BFR), BFR-id and BitString
are defined in [RFC8279]. A BitString indicates a continuous
sequence of bits indexed by an offset in the sequence. The leftmost
bit is bit 0 and corresponds to the value 0x80 of the leftmost octet
in the BitString.
3. Applicability
BIER and other bit-indexed methods that would leverage BitStrings
will generally require additional information in the packet to
complement the BitString. For instance, BIER has the concept of a
BFR-id and an Entropy value in the BIER header. Since those
additional fields depend on the bit-indexed method, they are expected
to be transported separately from the BitString. This specification
concentrates on the BitString and a group identifier which enables a
network to grow beyond the size of one bitString.
Within the context of "the Deterministic Networking (DetNet)
Architecture" [I-D.ietf-detnet-architecture] ), the "BIER-TE-based
OAM, Replication and Elimination"
[I-D.thubert-bier-replication-elimination] document details how BIER-
TE can be leveraged to activate the Deterministic Networking
Replication and Elimination functions in a manner that is abstract to
the data plane forwarding information. An adjacency, which is
represented by a bit in the BIER header, can be mapped in the data
plane to an Ethernet hop, a Label Switched Path, or it may correspond
to a loose or a strict IPv6 Source Routed Path.
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In the context of LLNs, the 6TiSCH Architecture
[I-D.ietf-6tisch-architecture] introduces the concept of a Track that
is a directional traffic-engineered path between a source and a
destination. A Track is indicated in a packet by a Source or
Destination IPv6 Address and a RPL Local Instance. The RPL Instance
is carried in an IPv6 packet as part of the RPL Packet Information
(RPI), and a bit in the RPI indicates whether the Instance is Local
to the Source or the Destination Address. The RPI can be compressed
as a RPI 6LoRH header (RPI-6LoRH) as described in [RFC8138].
The 6TiSCH requirements for DetNet [I-D.thubert-6tisch-4detnet]
indicate that a 6TiSCH Track may leverage replication and elimination
as defined in DetNet. This specification enables this behavior as
follows: if a BIER-6LoRH is positioned right after a RPI-6LoRH, then
the BitString in the BIER-6LoRH applies to the context of the Track
indicated by the source or destination address of the packet and the
local Instance ID associated to the source or destination of the
packet.
4. The BIER-6LoRH encoding
The BIER 6LoRH (BIER-6LoRH) is a Critical 6LoWPAN Routing Header that
provides a variable-size container for a BitString such as, a but not
limited to, a BIER BitString.
The capability to parse the BIER BitString 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| Control |6LoRHType 15-29| BitString |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- ... -+
Figure 1: The BIER-6LoRH
This specification provides a 5-bit Control field that can be used to
encode information that is specific to the BitString. The type and
size of the BitString are encoded in the 6LoRHType.
4.1. The Bit-by-bit BitStrings
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 BitStrings, and BIER allows to divide a network into
groups that partition the network so that a given BitString is
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locally significant to one group only. This specification uses the
5-bits Control field to encode the group.
When groups are used, it may be that a packet is sent to different
groups at the same time. In that case, multiple BIER-6LoRH headers
can be prepended to a same packet, each one for a different group.
As the packet flows along the multicast distribution tree, a BIER-
6LoRH header that has no more destination in a given branch may be
removed to make the packet shorter.
The encoding value indicates the size of the BitString. The size of
the BitString used in a given packet is smallest that can represent
all of the bits that are set for this particular packet, so for a
same network various sizes may be used for different packets
depending on the destinations.
4.2. The Enumeration BitStrings
For unicast and when very few destinations are targeted for a given
message, it may be that it is more economical to list the bit offsets
one by one than it is to represent the full BitString that can hold
all of the bit offsets.
In the Enumeration case, a BitString actually encodes the offset of
one bit as an unsigned integer, using the number of bits indicated in
the control field, and BitStrings are concatenated without
intermediate padding. The overall concatenation must be aligned to a
byte boundary. To achieve this, trailing bits are added to the right
of the concatenation as padding to the next byte boundary.
To optimize the compression, the lower numbers can be expressed with
less bits, and multiple Enumeration BIER-6LoRH headers may be used to
encode offsets that require different numbers of bits for their
representation.
4.3. Bloom Filters
A Bloom Filter can be seen as an additional compression technique for
the bitString representation. 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.ietf-roll-ccast]
specification employs Bloom Filters as a compact representation of a
match or non-match for elements in a set that may be larger than the
number of bits in the BitString.
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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 uses the 5-bits Control field to signal an Identifier
of the set of Hash functions being used to generate a certain
BitString, so as to enable the migration from a set of Hash functions
to the next.
4.4. Types of BIER-6LoRH header
The Type of a BIER-6LoRH header indicates the size of the BitString
and whether the BitString is operated as an uncompressed bit-by-bit
mapping, as an enumeration, or as a Bloom filter.
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+--------------+--------------+----------------------+--------------+
| BitString | Encoding | Control field | BitString |
| Type | | | Size |
+--------------+--------------+----------------------+--------------+
| 15 | bit-by-bit | Group ID | 8 bits |
+--------------+--------------+----------------------+--------------+
| 16 | bit-by-bit | Group ID | 16 bits |
+--------------+--------------+----------------------+--------------+
| 17 | bit-by-bit | Group ID | 32 bits |
+--------------+--------------+----------------------+--------------+
| 18 | bit-by-bit | Group ID | 56 bits |
+--------------+--------------+----------------------+--------------+
| 19 | bit-by-bit | Group ID | 96 bits |
+--------------+--------------+----------------------+--------------+
| 20 | bit-by-bit | Group ID | 160 bits |
+--------------+--------------+----------------------+--------------+
| 21 | bit-by-bit | Group ID | 256 bits |
+--------------+--------------+----------------------+--------------+
| 22 | Enumeration | Number of elements | 4 bits |
+--------------+--------------+----------------------+--------------+
| 23 | Enumeration | Number of elements | 6 bits |
+--------------+--------------+----------------------+--------------+
| 24 | Enumeration | Number of elements | 8 bits |
+--------------+--------------+----------------------+--------------+
| 25 | Bloom filter | Hash function Set ID | 8 bits |
+--------------+--------------+----------------------+--------------+
| 26 | Bloom filter | Hash function Set ID | 16 bits |
+--------------+--------------+----------------------+--------------+
| 27 | Bloom filter | Hash function Set ID | 48 bits |
+--------------+--------------+----------------------+--------------+
| 28 | Bloom filter | Hash function Set ID | 96 bits |
+--------------+--------------+----------------------+--------------+
| 29 | Bloom filter | Hash function Set ID | 160 bits |
+--------------+--------------+----------------------+--------------+
Table 1: The BIER-6LoRH Types
In order to address a potentially large number of devices, the
BitString 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. With this specification, a number of BIER-6LoRH headers of
a same type (bit-by-bit or Bloom filter) may be placed contiguously
in the packet. This results in a larger BitString that is the
concatenation of the BitStrings in the individual headers in the
order they are appearing in the packet.
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5. Implementation Status
A research-stage implementation was developed at Cisco's Paris
Innovation Lab (PIRL) by Zacharie Brodard. It was implemented on
OpenWSN open-source firmware and tested on the OpenMote-CC2538
hardware. It implements the header types 15, 16, 17, 18 and 19 (bit-
by-bit encoding without group ID) in order to allow a BIER-TE
protocol over IEE802.15.4e.
Links:
github: https://github.com/zach-b/openwsn-fw/tree/BIER
OpenWSN firmware: https://openwsn.atlassian.net/wiki/pages/
viewpage.action?pageId=688187
OpenMote hardware: http://www.openmote.com/
6. Security Considerations
The security considerations of [RFC8138] apply.
7. IANA Considerations
This document extends the IANA registry created by [RFC8138] for the
6LoWPAN Routing Header Type, and adds the following values:
15..29 : BIER-6LoRH [RFCthis]
8. Acknowledgments
9. References
9.1. Normative References
[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>.
[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,
<https://www.rfc-editor.org/info/rfc4944>.
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[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,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
RFC 8025, DOI 10.17487/RFC8025, November 2016,
<https://www.rfc-editor.org/info/rfc8025>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
9.2. Informative References
[I-D.eckert-bier-te-arch]
Eckert, T., Cauchie, G., Braun, W., and M. Menth, "Traffic
Engineering for Bit Index Explicit Replication BIER-TE",
draft-eckert-bier-te-arch-06 (work in progress), November
2017.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-19 (work
in progress), December 2018.
[I-D.ietf-detnet-architecture]
Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", draft-ietf-
detnet-architecture-10 (work in progress), December 2018.
[I-D.ietf-roll-ccast]
Bergmann, O., Bormann, C., Gerdes, S., and H. Chen,
"Constrained-Cast: Source-Routed Multicast for RPL",
draft-ietf-roll-ccast-01 (work in progress), October 2017.
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[I-D.thubert-6tisch-4detnet]
Thubert, P., "6TiSCH requirements for DetNet", draft-
thubert-6tisch-4detnet-01 (work in progress), June 2015.
[I-D.thubert-bier-replication-elimination]
Thubert, P., Eckert, T., Brodard, Z., and H. Jiang, "BIER-
TE extensions for Packet Replication and Elimination
Function (PREF) and OAM", draft-thubert-bier-replication-
elimination-03 (work in progress), March 2018.
[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,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://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,
<https://www.rfc-editor.org/info/rfc7228>.
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
Zacharie Brodard
Ecole Polytechnique
Route de Saclay
Palaiseau 91128
FRANCE
Phone: +33 6 73 73 35 09
Email: zacharie.brodard@polytechnique.edu
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Hao Jiang
Telecom Bretagne
2, rue de la Chataigneraie
Cesson-Sevigne 35510
FRANCE
Phone: +33 7 53 70 97 34
Email: hao.jiang@telecom-bretagne.eu
Geraldine Texier
Telecom Bretagne
2, rue de la Chataigneraie
Cesson-Sevigne 35510
FRANCE
Phone: +33 2 99 12 70 38
Email: geraldine.texier@telecom-bretagne.eu
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