Internet DRAFT - draft-ietf-6man-rpl-option
draft-ietf-6man-rpl-option
6MAN J. Hui
Internet-Draft JP. Vasseur
Intended status: Standards Track Cisco Systems, Inc
Expires: June 16, 2012 December 14, 2011
RPL Option for Carrying RPL Information in Data-Plane Datagrams
draft-ietf-6man-rpl-option-06
Abstract
The RPL protocol includes routing information in data-plane datagrams
to quickly identify inconsistencies in the routing topology. This
document describes the RPL Option for use among RPL routers to
include such routing information.
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 June 16, 2012.
Copyright Notice
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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. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5.1. DAG Inconsistency Attacks . . . . . . . . . . . . . . . . 9
5.2. DAO Inconsistency Attacks . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. Changes . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. 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 [RFC6206]. 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 defines 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 between RPL routers participating in the same
RPL Instance.
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
The RPL Option provides a mechanism to include routing information
with each datagram that a router forwards. When receiving datagrams
that include routing information, RPL routers process the routing
information to help maintain the routing topology.
Every RPL router along a packet's delivery path processes and updates
the RPL Option. If the received packet does not already contain a
RPL Option, the RPL router must insert a RPL Option before forwarding
it to another RPL router. This draft also specifies the use of IPv6-
in-IPv6 tunneling [RFC2473] when attaching a RPL option to a packet.
Use of tunneling ensures that the original packet remains unmodified
and that ICMP errors return to the RPL Option source rather than the
source of the original packet.
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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].
The two high order bits of the Option Type MUST be set to '01' and
the third bit is equal to '1'. With these bits, according to
[RFC2460], nodes that do not understand this option on a received
packet MUST discard the packet. Also, according to [RFC2460], the
values within the RPL Option are expected to change en-route. The
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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 sub-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
Datagrams sent between RPL routers MUST include a RPL Option or RPL
Source Route Header ([I-D.ietf-6man-rpl-routing-header]) and MAY
include both. A datagram including a SRH does not need to include a
RPL Option since both the source and intermediate routers ensure that
the SRH does not contain loops.
When the router is the source of the original packet and the
destination is known to be within the same RPL Instance, the router
SHOULD include the RPL Option directly within the original packet.
Otherwise, routers MUST use IPv6-in-IPv6 tunneling [RFC2473] and
place the RPL Option in the tunnel header. Using IPv6-in-IPv6
tunneling ensures that the delivered datagram remains unmodified and
that ICMPv6 errors generated by a RPL Option are sent back to the
router that generated the RPL Option.
A RPL router chooses the next RPL router that should process the
original packet as the tunnel exit-point. In some cases, the tunnel
exit-point will be the final RPL router along a path towards the
original packet's destination and the original packet will only
traverse a single tunnel. One example is when the final destination
or the destination's attachment router is known to be within the same
RPL Instance.
In other cases, the tunnel exit-point will not be the final RPL
router along a path and the original packet may traverse multiple
tunnels to reach the destination. One example is when a RPL router
is simply forwarding a packet to one of its DODAG Parents. In this
case, the RPL router sets the tunnel exit-point to a DODAG Parent.
When forwarding the original packet hop-by-hop, the RPL router only
makes a determination on the next hop towards the destination.
A RPL router receiving an IPv6-in-IPv6 packet destined to it
processes the tunnel packet as described in Section 3 of [RFC2473].
Before IPv6 decapsulation, the RPL router MUST process the RPL Option
if one exists. After IPv6 decapsulation, if the router determines
that it should forward the original packet to another RPL router it
MUST encapsulate the packet again using IPv6-in-IPv6 tunneling to
include the RPL Option. Fields within the RPL Option that do not
change hop-by-hop MUST remain the same as those received from the
prior tunnel.
RPL routers are responsible for ensuring that a RPL Option is only
used between RPL routers:
1. For datagrams destined to a RPL router, the router processes the
packet in the usual way. For instance, if the RPL Option was
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included using tunneled mode and the RPL router serves as the
tunnel endpoint, the router removes the outer IPv6 header, at the
same time removing the RPL Option as well.
2. Datagrams destined elsewhere within the same RPL Instance are
forwarded to the correct interface.
3. Datagrams destined to nodes outside the RPL Instance are dropped
if the outer-most IPv6 header contains a RPL Option not generated
by the RPL router forwarding the datagram.
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. Security Considerations
The RPL Option assists RPL routers in detecting routing
inconsistencies. The RPL message security mechanisms defined in
[I-D.ietf-roll-rpl] do not apply to the RPL Option.
5.1. DAG Inconsistency Attacks
Using the Down 'O' flag and SenderRank field, an attacker can cause
RPL routers to believe that a DAG inconsistency exists within the RPL
instance identified by the RPLInstanceID field. This attack would
cause a RPL router to reset its DIO Trickle timer and begin
transmitting DIO messages more frequently.
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_RANK_ERRORS per hour. A
RECOMMENDED value for MAX_RPL_OPTION_RANK_ERRORS is 20.
5.2. DAO Inconsistency Attacks
In storing mode, RPL routers maintain downward routing state. Under
normal operation, the RPL Option assists RPL routers in cleaning up
stale downward routing state by using the Forwarding-Error 'F' flag
to indicate that a datagram could not be delivered by a child and is
being sent back to try a different child. Using this flag, an
attacker can cause a RPL router to discard downward routing state.
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_FORWARD_ERRORS per hour.
A RECOMMENDED value for MAX_RPL_OPTION_FORWARD_ERRORS is 20.
In non-storing mode, only the LBR maintains downward routing state.
Because RPL routers do not maintain downward routing state, the RPL
Option cannot be used to mount such attacks.
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6. 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
sub-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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7. Acknowledgements
The authors thank Jari Arkko, Ralph Droms, Adrian Farrel, Stephen
Farrell, Richard Kelsey, Suresh Krishnan, Vishwas Manral, Erik
Nordmark, Pascal Thubert, Sean Turner, and Tim Winter, for their
comments and suggestions that helped shape this document.
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8. Changes
(This section to be removed by the RFC editor.)
Draft 06:
- Address IESG comments.
Draft 05:
- Address LC comments.
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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9. References
9.1. 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.
[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.
[RFC6206] Levis, P., Clausen, T., Hui, J., Gnawali, O., and J. Ko,
"The Trickle Algorithm", RFC 6206, March 2011.
9.2. Informative References
[I-D.ietf-6man-rpl-routing-header]
Hui, J., Vasseur, J., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with RPL",
draft-ietf-6man-rpl-routing-header-05 (work in progress),
November 2011.
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Authors' Addresses
Jonathan W. Hui
Cisco Systems, Inc
170 West Tasman Drive
San Jose, California 95134
USA
Phone: +408 424 1547
Email: jonhui@cisco.com
JP Vasseur
Cisco Systems, Inc
11, Rue Camille Desmoulins
Issy Les Moulineaux, 92782
France
Email: jpv@cisco.com
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