6MAN J. Hui
Internet-Draft Arch Rock Corporation
Intended status: Standards Track JP. Vasseur
Expires: April 14, 2012 Cisco Systems, Inc
October 12, 2011
RPL Option for Carrying RPL Information in Data-Plane Datagrams
draft-ietf-6man-rpl-option-04
Abstract
The RPL protocol requires data-plane datagrams to carry RPL routing
information that is processed by RPL routers when forwarding those
datagrams. This document describes the RPL Option for use within a
RPL domain.
Status of this Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Format of the RPL Option . . . . . . . . . . . . . . . . . . . 5
4. RPL Router Behavior . . . . . . . . . . . . . . . . . . . . . 7
5. RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10.1. Normative References . . . . . . . . . . . . . . . . . . . 13
10.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
RPL is a distance vector IPv6 routing protocol designed for Low power
and Lossy Networks (LLNs) [I-D.ietf-roll-rpl]. Such networks are
typically constrained in energy and/or channel capacity. To conserve
precious resources, a routing protocol must generate control traffic
sparingly. However, this is at odds with the need to quickly
propagate any new routing information to resolve routing
inconsistencies quickly.
To help minimize resource consumption, RPL uses a slow proactive
process to construct and maintain a routing topology but a reactive
and dynamic process to resolving routing inconsistencies. In the
steady state, RPL maintains the routing topology using a low-rate
beaconing process. However, when RPL detects inconsistencies that
may prevent proper datagram delivery, RPL temporarily increases the
beacon rate to quickly resolve those inconsistencies. This dynamic
rate control operation is governed by the use of dynamic timers also
referred to as "Trickle" timers and defined in
[I-D.ietf-roll-trickle]. In contrast to other routing protocols (e.g
OSPF [RFC2328]), RPL detects routing inconsistencies using data-path
verification, by including routing information within the datagram
itself. In doing so, repair mechanisms operate only as needed,
allowing the control and data planes to operate on similar time
scales. The main motivation for data path verification in LLNs is
that control plane traffic should be carefully bounded with respect
to the data traffic. Intuitively, there is no need to solve routing
issues (which may be temporary) in the absence of data traffic.
The RPL protocol constructs a Directed Acyclic Graph (DAG) that
attempts to minimize path costs to the DAG root according to a set of
metric and objective functions. There are circumstances where loops
may occur, and RPL is designed to use a data-path loop detection
method. This is one of the known requirements of RPL and other data-
path usage might be defined in the future.
To that end, this document proposes a new IPv6 option, called the RPL
Option, to be carried within the IPv6 Hop-by-Hop header. The RPL
Option is only for use within a RPL domain.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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2. Overview
Datagrams sent between nodes within a RPL domain MUST include a RPL
Option or RPL Source Route Header (SRH) and MAY include both. When a
RPL Border Router inserts a RPL Option, it MUST do so by using IPv6-
in-IPv6 tunneling, as specified in [RFC2473]. Use of tunneling
ensures that the datagram is delivered unmodified and that ICMP
errors return to the RPL Option source rather than the source of the
original datagram.
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3. Format of the RPL Option
The RPL Option is carried in an IPv6 Hop-by-Hop Options header,
immediately following the IPv6 header. This option has an alignment
requirement of 2n. The option has the following format:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|O|R|F|0|0|0|0|0| RPLInstanceID | SenderRank |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| (sub-TLVs) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: RPL Option
Option Type: TBD by IANA.
Opt Data Len: 8-bit field indicating the length of the option, in
octets, excluding the Option Type and Opt Data Len fields.
Down 'O': 1-bit flag as defined in Section 11.2 of
[I-D.ietf-roll-rpl]. The processing shall follow the rules
described in Section 11.2 of [I-D.ietf-roll-rpl].
Rank-Error 'R': 1-bit flag as defined in Section 11.2 of
[I-D.ietf-roll-rpl]. The processing shall follow the rules
described in Section 11.2 of [I-D.ietf-roll-rpl].
Forwarding-Error 'F': 1-bit flag as defined in Section 11.2 of
[I-D.ietf-roll-rpl]. The processing shall follow the rules
described in Section 11.2 of [I-D.ietf-roll-rpl].
RPLInstanceID: 8-bit field as defined in Section 11.2 of
[I-D.ietf-roll-rpl]. The processing shall follow the rules
described in Section 11.2 of [I-D.ietf-roll-rpl].
SenderRank: 16-bit field as defined in Section 11.2 of
[I-D.ietf-roll-rpl]. The processing shall follow the rules
described in Section 11.2 of [I-D.ietf-roll-rpl].
Values within the RPL Option are expected to change en-route. Nodes
that do not understand the RPL Option MUST discard the packet. Thus,
according to [RFC2460] the two high order bits of the Option Type
must be equal set to '01' and the third bit is equal to '1'. The RPL
Option Data Length is variable.
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The action taken by using the RPL Option and the potential set of
sub-TLVs carried within the RPL Option MUST be specified by the RFC
of the protocol that use that option. No TLVs are defined in this
document. A RPL device MUST skip over any unrecognized sub-TLVs and
attempt to process any additional sub-TLVs that may appear after.
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4. RPL Router Behavior
To deliver an IPv6 datagram to its destination, a router may need to
insert a new RPL Option. Routers MUST use IPv6-in-IPv6 tunneling, as
specified in [RFC2473] to include a new RPL Option in datagrams that
are sourced by other nodes. Using IPv6-in-IPv6 tunneling ensures
that the delivered datagram remains unmodified and that ICMPv6 errors
generated by inserting the RPL Option are sent back to the router
that generated the routing header.
To avoid fragmentation, it is desirable to employ MTU sizes that
allow for the header expansion (i.e. at least 1280 + 40 (outer IP
header) + RPL_OPTION_MAX_SIZE), where RPL_OPTION_MAX_SIZE is the
maximum RPL Option header size for a given RPL network. To take
advantage of this, however, the communicating endpoints need to be
aware of the MTU along the path (i.e. through Path MTU Discovery).
Unfortunately, the larger MTU size may not be available on all links
(e.g. 1280 octets on 6LoWPAN links). However, it is expected that
much of the traffic on these types of networks consists of much
smaller messages than the MTU, so performance degradation through
fragmentation would be limited.
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5. RPL Border Router Behavior
RPL Border Routers (referred to as LBRs in
[I-D.ietf-roll-terminology]) are responsible for ensuring that a RPL
Option is only used within a RPL domain.
For datagrams destined to the RPL Border Router, the router processes
the packet in the usual way. For instance, if the RPL Option was
included using tunneled mode and the RPL Border Router serves as the
tunnel endpoint, the router removes the outer IPv6 header, at the
same time removing the RPL Option as well.
Datagrams destined elsewhere within the same RPL domain are forwarded
to the correct interface.
Datagrams destined to nodes outside the RPL domain are dropped if the
outer-most IPv6 header contains a RPL Option.
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6. Security Considerations
This option may be used to mount several potential attacks since
routers may be flooded by bogus datagrams containing the RPL Option.
In particular, an inconsistent Rank value can cause a RPL router to
reset its DIO Trickle timer.
In order to avoid any unacceptable impact on network operations, an
implementation MAY limit the number of triggers caused by receiving a
RPL Option to no greater than MAX_RPL_OPTION_TRIGGERS per hour. A
RECOMMENDED value for MAX_RPL_OPTION_TRIGGERS is 20.
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7. IANA Considerations
IANA is requested to reserve a new value in the Destination Options
and Hop-by-Hop Options registry. The proposed value to be confirmed
by IANA is:
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
TBD 01 1 TBD RPL Option [RFCthis]
As specified in [RFC2460], the first two bits indicate that the IPv6
node MUST discard the packet if it doesn't recognize the option type,
and the third bit indicates that the Option Data may change en-route.
The remaining bits serve as the option type and are TBD by IANA.
IANA is requested to create a registry called RPL-option-TLV, for the
TLVs carried in the RPL Option header. New codes may be allocated
only by IETF Review [RFC5226]. The type field is an 8-bit field
whose value be between 0 and 255, inclusive.
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8. Acknowledgements
The authors thank Jari Arkko, Richard Kelsey, Suresh Krishnan,
Vishwas Manral, Erik Nordmark, Pascal Thubert, and Tim Winter, for
their comments and suggestions that helped shape this document.
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9. Changes
(This section to be removed by the RFC editor.)
Draft 04:
- Clarify when the RPL Option is used.
- Updated text on recommendations for avoiding fragmentation.
- Specify skip-over-and-continue policy for unrecognized sub-TLVs.
- Change use of IPv6-in-IPv6 tunneling from SHOULD to MUST.
- Specify RPL Border Router operations in terms of forwarding
decision outcomes.
- Expand security section.
Draft 03:
- Removed any presumed values that are TBD by IANA.
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10. References
10.1. Normative References
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-19 (work in
progress), March 2011.
[I-D.ietf-roll-trickle]
Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", draft-ietf-roll-trickle-08 (work
in progress), January 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, December 1998.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
10.2. Informative References
[]
Hui, J., Thubert, P., and J. Vasseur, "Using RPL Headers
Without IP-in-IP", draft-hui-6man-rpl-headers-00 (work in
progress), July 2010.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-06 (work in
progress), September 2011.
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Authors' Addresses
Jonathan W. Hui
Arch Rock Corporation
501 2nd St. Ste. 410
San Francisco, California 94107
USA
Phone: +415 692 0828
Email: jhui@archrock.com
JP Vasseur
Cisco Systems, Inc
11, Rue Camille Desmoulins
Issy Les Moulineaux, 92782
France
Email: jpv@cisco.com
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