6MAN J. Hui
Internet-Draft Arch Rock Corporation
Intended status: Standards Track JP. Vasseur
Expires: August 12, 2011 Cisco Systems, Inc
February 8, 2011
RPL Option for Carrying RPL Information in Data-Plane Datagrams
draft-ietf-6man-rpl-option-02
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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This Internet-Draft will expire on August 12, 2011.
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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 . . . . . . . . . . . . . . . . . . . . . 6
5. RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 7
6. Usage of the RPL Option . . . . . . . . . . . . . . . . . . . 8
7. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Security Considerations . . . . . . . . . . . . . . . . . . . 12
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
11.1. Normative References . . . . . . . . . . . . . . . . . . . 13
11.2. 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 [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 Low power
and Lossy Networks (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 being forwarded within a RPL domain MUST include a RPL
Option. For datagrams sourced within a RPL domain, the RPL Option
MAY be included in the datagram itself. For datagrams sourced
outside a RPL domain, IPv6-in-IPv6 tunneling, as specified in
[RFC2473] SHOULD be used to include a RPL Option. When tunneling,
the router MUST prepend a new IPv6 header and IPv6 Hop-by-Hop Options
header containing the RPL Option to the existing datagram. 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.
To help avoid IP-layer fragmentation, the RPL Option has a maximum
size of RPL_OPTION_MAX_SIZE octets and links within a RPL domain
SHOULD have a MTU of at least 1280 + 44 (outer IP header, Hop-by-Hop
Option header, Option header) + RPL_OPTION_MAX_SIZE + (additional
extension headers or options needed within RPL domain).
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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
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 of
[I-D.ietf-roll-rpl].
Rank-Error 'R': 1-bit flag as defined in Section 11 of
[I-D.ietf-roll-rpl].
Forwarding-Error 'F': 1-bit flag as defined in Section 11 of
[I-D.ietf-roll-rpl].
RPLInstanceID: 8-bit field as defined in Section 11 of
[I-D.ietf-roll-rpl].
SenderRank: 16-bit field as defined in Section 11 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.
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.
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4. RPL Router Behavior
RPL controls when and what information is to be placed in a packet.
If RPL requires a router to include a RPL Option where one does not
already exist, routers SHOULD use IPv6-in-IPv6 tunneling, as
specified in [RFC2473] to include a RPL Option in datagrams that are
sourced by other nodes. Using IPv6-in-IPv6 tunneling ensures that
the original datagram is delivered unmodified.
Performing IP-in-IP encapsulation may grow the datagram to a size
larger than the IPv6 min MTU of 1280 octets. To help avoid IP-layer
fragmentation caused by IP-in-IP encapsulation, links within a RPL
domain SHOULD be configured with a MTU of at least 1280 + 44 (outer
IP header, Hop-by-Hop Option header, Option header) +
RPL_OPTION_MAX_SIZE + (additional extension headers or options needed
within RPL domain).
In very specific cases, IPv6-in-IPv6 tunneling may be undesirable due
to the added cost and complexity required to process and carry a
datagram with two IPv6 headers. [I-D.hui-6man-rpl-headers] describes
how to avoid using IPv6-in-IPv6 tunneling in such specific cases and
the risks involved.
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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 entering the RPL domain, RPL Border Routers MUST drop
received datagrams that contain a RPL Option in the IPv6 Extension
headers.
For datagrams exiting the RPL domain, RPL Border Routers MUST remove
the RPL Option from the datagram. If the RPL Option was included
using tunneled mode and the RPL Border Router serves as the tunnel
end-point, removing the outer IPv6 header serves to remove the RPL
Option as well. Otherwise, the RPL Border Router assumes that the
RPL Option was included using transport mode and MUST remove the RPL
Option from the IPv6 Hop-by-Hop Option header.
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6. Usage of the RPL Option
The RPL Option is only for use within a RPL domain. RPL routers MUST
process and include the RPL Option when forwarding datagrams to other
nodes within the RPL domain. Routers on the edge of a RPL domain
MUST remove the RPL Option when forwarding datagrams to nodes outside
the RPL domain.
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7. Protocol Constants
RPL_OPTION_MAX_SIZE 128
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8. Acknowledgements
The authors thank 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. 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
--------- --- --- ------- ----------------- ----------
0x6b 01 1 01011 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 to as the option type are are '01011' (to be
confirmed 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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10. Security Considerations
This option may be used a several potential attacks since routers may
be flooded by bogus datagram containing the RPL option. It is thus
RECOMMENDED for routers to implement a rate limiter for datagrams
using the RPL Option.
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11. References
11.1. 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-18 (work in
progress), February 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.
11.2. 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-04 (work in
progress), September 2010.
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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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