6MAN J. Hui
Internet-Draft Arch Rock Corporation
Intended status: Standards Track JP. Vasseur
Expires: April 26, 2011 Cisco Systems, Inc
October 23, 2010
RPL Option for Carrying RPL Information in Data-Plane Datagrams
draft-ietf-6man-rpl-option-01
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 April 26, 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 . . . . . . . . . . . . . . . . . . . . . 7
5. RPL Border Router Behavior . . . . . . . . . . . . . . . . . . 8
6. Usage of the RPL Option . . . . . . . . . . . . . . . . . . . 9
7. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
10. Security Considerations . . . . . . . . . . . . . . . . . . . 13
11. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
12.1. Normative References . . . . . . . . . . . . . . . . . . . 15
12.2. Informative References . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16
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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 approach 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. Such a dynamic
rate of control packets operation is governed by the use of dynamic
timers also referred to as "trickle" timers and defined in
[I-D.ietf-roll-trickle]. By contrast with other routing protocols
such as OSPF ([RFC2328]), RPL detects routing inconsistencies using
data-path verification, by including routing information within the
datagram itself. Data-path verification quickly detects and resolves
inconsistencies when routes are needed by the data flow 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: there is no need to solve a 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 for use only 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] MUST be used to include a RPL Option. When forwarding the
datagram, 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. The RPL 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:
Down 'O': 1-bit flag indicating whether the packet is expected to
progress Up or Down. A router sets the 'O' flag when the
packet is expected to progress Down (using DAO routes), and
clears it when forwarding toward the DODAG root (to a node with
a lower rank). A host or RPL leaf node MUST set the 'O' flag
to 0.
Rank-Error 'R': 1-bit flag indicating whether a rank error was
detected. A rank error is detected when there is a mismatch in
the relative ranks and the direction as indicated in the 'O'
bit. A host or RPL leaf node MUST set the 'R' bit to 0.
Forwarding-Error 'F': 1-bit flag indicating that this node can not
forward the packet further towards the destination. The 'F'
bit might be set by a child node that does not have a route to
destination for a packet with the Down 'O' bit set. A host or
RPL leaf node MUST set the 'F' bit to 0.
RPLInstanceID: 8-bit field indicating the DODAG instance along which
the packet is sent.
SenderRank: 16-bit field set to zero by the source and to
DAGRank(rank) by a router that forwards inside the RPL network.
Values within the RPL option are expected to change en-route. Nodes
that do not understand the RPL option MUST discard the packet. Thus,
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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 currently defined.
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4. RPL Router Behavior
Routers MUST include a RPL Option when forwarding datagrams that do
not already contain a RPL Option. If one does not already exist,
routers MUST use IPv6-in-IPv6 tunneling, as specified in [RFC2473] to
include a RPL Option in datagrams that are sourced by other nodes.
This 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).
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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 and update the IPv6 Payload Length
field accordingly.
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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, 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
The RPL option requires an IPv6 Option Number.
HEX act chg rest
--- --- --- -----
1 01 1 01011
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.
This document also creates a new IANA registry for the sub-TLVs. No
sub-TLVs are defined in this specification. The policy for this
registry [RFC5226] is IETF Review.
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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. Changes
(This section to be removed by the RFC editor.)
Draft 01:
- Specify that a node must discard the packet if it doesn't
recognize the RPL option.
- Include RPL loop detection bits in the base header such that an
IPv6 Hop-by-Hop Option header with the minimal RPL option consumes
only 8 octets.
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12. References
12.1. Normative References
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., Brandt, A., Clausen, T., Hui, J.,
Kelsey, R., Levis, P., Networks, D., Struik, R., and J.
Vasseur, "RPL: IPv6 Routing Protocol for Low power and
Lossy Networks", draft-ietf-roll-rpl-13 (work in
progress), October 2010.
[I-D.ietf-roll-trickle]
Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", draft-ietf-roll-trickle-04 (work
in progress), August 2010.
[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.
12.2. Informative References
[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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