Internet Engineering Task Force (IETF) E. Kim
Request for Comments: 6606 ETRI
Category: Informational D. Kaspar
ISSN: 2070-1721 Simula Research Laboratory
C. Gomez
Universitat Politecnica de Catalunya/Fundacio i2CAT
C. Bormann
Universitaet Bremen TZI
May 2012
Problem Statement and Requirements for
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Routing
Abstract
IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs) are
formed by devices that are compatible with the IEEE 802.15.4
standard. However, neither the IEEE 802.15.4 standard nor the
6LoWPAN format specification defines how mesh topologies could be
obtained and maintained. Thus, it should be considered how 6LoWPAN
formation and multi-hop routing could be supported.
This document provides the problem statement and design space for
6LoWPAN routing. It defines the routing requirements for 6LoWPANs,
considering the low-power and other particular characteristics of the
devices and links. The purpose of this document is not to recommend
specific solutions but to provide general, layer-agnostic guidelines
about the design of 6LoWPAN routing that can lead to further analysis
and protocol design. This document is intended as input to groups
working on routing protocols relevant to 6LoWPANs, such as the IETF
ROLL WG.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6606.
Kim, et al. Informational [Page 1]RFC 6606 6LoWPAN Routing Requirements May 2012
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Problem Statement ...............................................2
2. Terminology .....................................................5
3. Design Space ....................................................5
3.1. Reference Network Model ....................................6
4. Scenario Considerations and Parameters for 6LoWPAN Routing ......8
5. 6LoWPAN Routing Requirements ...................................13
5.1. Support of 6LoWPAN Device Properties ......................13
5.2. Support of 6LoWPAN Link Properties ........................15
5.3. Support of 6LoWPAN Characteristics ........................18
5.4. Support of Security .......................................22
5.5. Support of Mesh-Under Forwarding ..........................25
5.6. Support of Management .....................................26
6. Security Considerations ........................................27
7. Acknowledgments ................................................27
8. References .....................................................28
8.1. Normative References ......................................28
8.2. Informative References ....................................29
1. Problem Statement
6LoWPANs are formed by devices that are compatible with the
IEEE 802.15.4 standard [IEEE802.15.4]. Most of the LoWPAN devices
are distinguished by their low bandwidth, short range, scarce memory
capacity, limited processing capability, and other attributes of
inexpensive hardware. The characteristics of nodes participating in
LoWPANs are assumed to be those described in the 6LoWPAN problem
statement [RFC4919], and in the IPv6 over IEEE 802.15.4 document
[RFC4944], which has specified how to carry IPv6 packets over
IEEE 802.15.4 and similar networks. Whereas IEEE 802.15.4
distinguishes two types of devices called full-function devices
(FFDs) and reduced-function devices (RFDs), this distinction is based
Kim, et al. Informational [Page 2]RFC 6606 6LoWPAN Routing Requirements May 2012
on some features of the Medium Access Control (MAC) layer that are
not always in use. Hence, the distinction is not made in this
document. Nevertheless, some 6LoWPAN nodes may limit themselves to
the role of hosts only, whereas other 6LoWPAN nodes may take part in
routing. This host/ router distinction can correlate with the
processing and storage capabilities of the device and power available
in a similar way to the idea of RFDs and FFDs.
IEEE 802.15.4 networks support star and mesh topologies. However,
neither the IEEE 802.15.4 standard nor the 6LoWPAN format
specification ([RFC4944]) define how mesh topologies could be
obtained and maintained. Thus, 6LoWPAN formation and multi-hop
routing can be supported either below the IP layer (the adaptation
layer or Logical Link Control (LLC)) or the IP layer. (Note that in
the IETF, the term "routing" usually, but not always [RFC5556],
refers exclusively to the formation of paths and the forwarding at
the IP layer. In this document, we distinguish the layer at which
these services are performed by the terms "route-over" and
"mesh-under". See Sections 2 and 3.) A number of IP routing
protocols have been developed in various IETF working groups.
However, these existing routing protocols may not satisfy the
requirements of multi-hop routing in 6LoWPANs, for the following
reasons:
o 6LoWPAN nodes have special types and roles, such as nodes drawing
their power from primary batteries, power-affluent nodes,
mains-powered and high-performance gateways, data aggregators,
etc. 6LoWPAN routing protocols should support multiple device
types and roles.
o More stringent requirements apply to LoWPANs, as opposed to
higher-performance or non-battery-operated networks. 6LoWPAN
nodes are characterized by small memory sizes and low processing
power, and they run on very limited power supplied by primary
non-rechargeable batteries (a few KB of RAM, a few dozen KB of
ROM/ flash memory, and a few MHz of CPU is typical). A node's
lifetime is usually defined by the lifetime of its battery.
o Handling sleeping nodes is very critical in LoWPANs, more so than
in traditional ad hoc networks. LoWPAN nodes might stay in sleep
mode most of the time. Taking advantage of appropriate times for
transmissions is important for efficient packet forwarding.
o Routing in 6LoWPANs might possibly translate to a simpler problem
than routing in higher-performance networks. LoWPANs might be
either transit networks or stub networks. Under the assumption
that LoWPANs are never transit networks (as implied by [RFC4944]),
Kim, et al. Informational [Page 3]RFC 6606 6LoWPAN Routing Requirements May 2012
routing protocols may be drastically simplified. This document
will focus on the requirements for stub networks. Additional
requirements may apply to transit networks.
o Routing in LoWPANs might possibly translate to a harder problem
than routing in higher-performance networks. Routing in LoWPANs
requires power optimization, stable operation in lossy
environments, etc. These requirements are not easily satisfiable
all at once [ROLL-PROTOCOLS].
These properties create new challenges for the design of routing
within LoWPANs.
The 6LoWPAN problem statement [RFC4919] briefly mentions four
requirements for routing protocols:
(a) low overhead on data packets
(b) low routing overhead
(c) minimal memory and computation requirements
(d) support for sleeping nodes (consideration of battery savings)
These four high-level requirements describe the basic requirements
for 6LoWPAN routing. Based on the fundamental features of 6LoWPANs,
more detailed routing requirements, which can lead to further
analysis and protocol design, are presented in this document.
Considering the problems above, detailed 6LoWPAN routing requirements
must be defined. Application-specific features affect the design of
6LoWPAN routing requirements and corresponding solutions. However,
various applications can be profiled by similar technical
characteristics, although the related detailed requirements might
differ (e.g., a few dozen nodes in a home lighting system need
appropriate scalability for the system's applications, while millions
of nodes for a highway infrastructure system also need appropriate
scalability).
This routing requirements document states the routing requirements of
6LoWPAN applications in general, providing examples for different
cases of routing. It does not imply that a single routing solution
will be favorable for all 6LoWPAN applications, and there is no
requirement for different routing protocols to run simultaneously.
Kim, et al. Informational [Page 4]RFC 6606 6LoWPAN Routing Requirements May 2012
2. Terminology
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 [RFC2119].
Readers are expected to be familiar with all the terms and concepts
that are discussed in "IPv6 over Low-Power Wireless Personal Area
Networks (6LoWPANs): Overview, Assumptions, Problem Statement, and
Goals" [RFC4919] and "Transmission of IPv6 Packets over IEEE 802.15.4
Networks" [RFC4944].
This specification makes use of the terminology defined in
[6LoWPAN-ND].
3. Design Space
Apart from a wide variety of conceivable routing algorithms for
6LoWPANs, it is possible to perform routing in the IP layer (using a
route-over approach) or below IP, as defined by the 6LoWPAN format
document [RFC4944] (using the mesh-under approach). See Figure 1.
The route-over approach relies on IP routing and therefore supports
routing over possibly various types of interconnected links.
Note: The ROLL WG is now working on route-over approaches for
Low-power and Lossy Networks (LLNs), not specifically for 6LoWPANs.
This document focuses on 6LoWPAN-specific requirements; it may be
used in conjunction with the more application-oriented requirements
defined by the ROLL WG.
The mesh-under approach performs the multi-hop communication below
the IP link. The most significant consequence of the mesh-under
mechanism is that the characteristics of IEEE 802.15.4 directly
affect the 6LoWPAN routing mechanisms, including the use of 64-bit
(or 16-bit short) link-layer addresses instead of IP addresses. A
6LoWPAN would therefore be seen as a single IP link.
Most statements in this document consider both the route-over and
mesh-under cases.
Kim, et al. Informational [Page 5]
RFC 6606 6LoWPAN Routing Requirements May 2012
Figure 1 shows the place of 6LoWPAN routing in the entire network
stack.
+---------------------------+ +-----------------------------+
| Application Layer | | Application Layer |
+---------------------------+ +-----------------------------+
| Transport Layer (TCP/UDP) | | Transport Layer (TCP/UDP) |
+---------------------------+ +-----------------------------+
| Network Layer (IPv6) | | Network +---------+ |
+---------------------------+ | Layer | Routing | |
| 6LoWPAN | | (IPv6) +---------+ |
| Adaptation | +-----------------------------+
| Layer +----------+ | | 6LoWPAN Adaptation Layer |
+--------------| Routing* |-+ +-----------------------------+
| 802.15.4 MAC +----------+ | | 802.15.4 MAC |
+---------------------------+ +-----------------------------+
| 802.15.4 PHY | | 802.15.4 PHY |
+---------------------------+ +-----------------------------+
* Here, "Routing" is not equivalent to IP routing,
but includes the functionalities of path computation and
forwarding under the IP layer.
The term "Routing" is used in the figure in order to
illustrate which layer handles path computation and
packet forwarding in mesh-under as compared to route-over.
Figure 1: Mesh-Under Routing (Left) and Route-Over Routing (Right)
In order to avoid packet fragmentation and the overhead for
reassembly, routing packets should fit into a single IEEE 802.15.4
physical frame, and application data should not be expanded to an
extent that they no longer fit.
3.1. Reference Network Model
For multi-hop communication in 6LoWPANs, when a route-over mechanism
is in use, all routers (i.e., 6LoWPAN Border Routers (6LBRs) and
6LoWPAN Routers (6LRs)) perform IP routing within the stub network
(see Figure 2). In this case, the link-local scope covers the set of
nodes within symmetric radio range of a node.
When a LoWPAN follows the mesh-under configuration, the 6LBR is the
only IPv6 router in the LoWPAN (see Figure 3). This means that the
IPv6 link-local scope includes all nodes in the LoWPAN. For this, a
mesh-under mechanism MUST be provided to support multi-hop
transmission.
Kim, et al. Informational [Page 6]RFC 6606 6LoWPAN Routing Requirements May 2012
h h
/ | 6LBR: 6LoWPAN Border Router
6LBR -- 6LR --- 6LR --- h 6LR: 6LoWPAN Router
/ \ h: Host
h 6LR --- h
|
/ \
6LR - 6LR -- h
Figure 2: An Example of a Route-Over LoWPAN
h h
/ | 6LBR: 6LoWPAN Border Router
6LBR --- m --- m --- h m: mesh-under forwarder
/ \ h: Host
h m --- h
|
/ \
m - m -- h
Figure 3: An Example of a Mesh-Under LoWPAN
Note than in both mesh-under and route-over networks, there is no
expectation of topologically based address assignment in the 6LoWPAN.
Instead, addresses are typically assigned based on the EUI-64
addresses assigned at manufacturing time to nodes, or based on a
(from a topological point of view) more or less random process
assigning 16-bit MAC addresses to individual nodes. Within a
6LoWPAN, there is therefore no opportunity for aggregation or
summarization of IPv6 addresses beyond the sharing of (one or more)
common prefixes.
Not all devices that are within radio range of each other need to be
part of the same LoWPAN. When multiple LoWPANs are formed with
globally unique IPv6 addresses in the 6LoWPANs, and device (a) of
LoWPAN [A] wants to communicate with device (b) of LoWPAN [B], the
normal IPv6 mechanisms will be employed. For route-over, the IPv6
address of (b) is set as the destination of the packets, and the
devices perform IP routing to the 6LBR for these outgoing packets.
For mesh-under, there is one IP hop from device (a) to the 6LBR of
[A], no matter how many radio hops they are apart from each other.
This, of course, assumes the existence of a mesh-under routing
protocol in order to reach the 6LBR. Note that a default route to
the 6LBR could be inserted into the 6LoWPAN routing system for both
route-over and mesh-under.
Kim, et al. Informational [Page 7]RFC 6606 6LoWPAN Routing Requirements May 2012
4. Scenario Considerations and Parameters for 6LoWPAN Routing
IP-based LoWPAN technology is still in its early stage of
development, but the range of conceivable usage scenarios is
tremendous. The numerous possible applications of sensor networks
make it obvious that mesh topologies will be prevalent in LoWPAN
environments and robust routing will be a necessity for expedient
communication. Research efforts in the area of sensor networking
have put forth a large variety of multi-hop routing algorithms
[Bulusu]. Most related work focuses on optimizing routing for
specific application scenarios, which can be realized using several
modes of communication, including the following [Watteyne]:
o Flooding (in very small networks)
o Hierarchical routing
o Geographic routing
o Self-organizing coordinate routing
Depending on the topology of a LoWPAN and the application(s) running
over it, different types of routing may be used. However, this
document abstracts from application-specific communication and
describes general routing requirements valid for overall routing in
LoWPANs.
The following parameters can be used to describe specific scenarios
in which the candidate routing protocols could be evaluated.
a. Network Properties:
* Number of Devices, Density, and Network Diameter:
These parameters usually affect the routing state directly
(e.g., the number of entries in a routing table or neighbor
list). Especially in large and dense networks, policies must
be applied for discarding "low-quality" and stale routing
entries in order to prevent memory overflow.
* Connectivity:
Due to external factors or programmed disconnections, a LoWPAN
can be in several states of connectivity -- anything in the
range from "always connected" to "rarely connected". This
poses great challenges to the dynamic discovery of routes
across a LoWPAN.
Kim, et al. Informational [Page 8]RFC 6606 6LoWPAN Routing Requirements May 2012
* Dynamicity (including mobility):
Location changes can be induced by unpredictable external
factors or by controlled motion, which may in turn cause route
changes. Also, nodes may dynamically be introduced into a
LoWPAN and removed from it later. The routing state and the
volume of control messages may heavily depend on the number of
moving nodes in a LoWPAN and their speed, as well as how
quickly and frequently environmental characteristics
influencing radio propagation change.
* Deployment:
In a LoWPAN, it is possible for nodes to be scattered randomly
or to be deployed in an organized manner. The deployment can
occur at once, or as an iterative process, which may also
affect the routing state.
* Spatial Distribution of Nodes and Gateways:
Network connectivity depends on the spatial distribution of
the nodes and on other factors, such as device number,
density, and transmission range. For instance, nodes can be
placed on a grid, or randomly located in an area (as can be
modeled by a two-dimensional Poisson distribution), etc.
Assuming a random spatial distribution, an average of 7
neighbors per node are required for approximately 95% network
connectivity (10 neighbors per node are needed for 99%
connectivity) [Kuhn]. In addition, if the LoWPAN is connected
to other networks through infrastructure nodes called
gateways, the number and spatial distribution of these
gateways affect network congestion and available data rate,
among other things.
* Traffic Patterns, Topology, and Applications:
The design of a LoWPAN and the requirements for its
application have a big impact on the network topology and the
most efficient routing type to be used. For different traffic
patterns (point-to-point, multipoint-to-point, point-to-
multipoint) and network architectures, various routing
mechanisms have been developed, such as data-centric, event-
driven, address-centric, and geographic routing.
* Classes of Service:
For mixing applications of different criticality on one
LoWPAN, support of multiple classes of service may be required
in resource-constrained LoWPANs and may require a new routing
protocol functionality.
Kim, et al. Informational [Page 9]RFC 6606 6LoWPAN Routing Requirements May 2012
* Security:
LoWPANs may carry sensitive information and require a high
level of security support where the availability, integrity,
and confidentiality of data are of prime relevance. Secured
messages cause overhead and affect the power consumption of
LoWPAN routing protocols.
b. Node Parameters:
* Processing Speed and Memory Size:
These basic parameters define the maximum size of the routing
state and the maximum complexity of its processing. LoWPAN
nodes may have different performance characteristics, queuing
strategies, and queue buffer sizes.
* Power Consumption and Power Source:
The number of battery- and mains-powered nodes and their
positions in the topology created by them in a LoWPAN affect
routing protocols in their selection of paths that optimize
network lifetime.
* Transmission Range:
This parameter affects routing. For example, a high
transmission range may cause a dense network, which in turn
results in more direct neighbors of a node, higher
connectivity, and a larger routing state.
* Traffic Pattern:
This parameter affects routing, since highly loaded nodes
(either because they are the source of packets to be
transmitted or due to forwarding) may contribute to higher
delivery delays and may consume more energy than lightly
loaded nodes. This applies to both data packets and routing
control messages.
Kim, et al. Informational [Page 10]RFC 6606 6LoWPAN Routing Requirements May 2012
c. Link Parameters:
This section discusses link parameters that apply to
IEEE 802.15.4 legacy mode (i.e., not making use of improved
modulation schemes).
* Throughput:
The maximum user data throughput of a bulk data transmission
between a single sender and a single receiver through an
unslotted IEEE 802.15.4 2.4 GHz channel in ideal conditions is
as follows [Latre]:
+ 16-bit MAC addresses, unreliable mode: 151.6 kbit/s
+ 16-bit MAC addresses, reliable mode: 139.0 kbit/s
+ 64-bit MAC addresses, unreliable mode: 135.6 kbit/s
+ 64-bit MAC addresses, reliable mode: 124.4 kbit/s
Throughput for the 915 MHz band is as follows:
+ 16-bit MAC addresses, unreliable mode: 31.1 kbit/s
+ 16-bit MAC addresses, reliable mode: 28.6 kbit/s
+ 64-bit MAC addresses, unreliable mode: 27.8 kbit/s
+ 64-bit MAC addresses, reliable mode: 25.6 kbit/s
Throughput for the 868 MHz band is as follows:
+ 16-bit MAC addresses, unreliable mode: 15.5 kbit/s
+ 16-bit MAC addresses, reliable mode: 14.3 kbit/s
+ 64-bit MAC addresses, unreliable mode: 13.9 kbit/s
+ 64-bit MAC addresses, reliable mode: 12.8 kbit/s
Kim, et al. Informational [Page 11]RFC 6606 6LoWPAN Routing Requirements May 2012
* Latency:
Latency ranges -- depending on payload size -- of a frame
transmission between a single sender and a single receiver
through an unslotted IEEE 802.15.4 2.4 GHz channel in ideal
conditions are as shown below [Latre]. For unreliable mode,
the actual latency is provided. For reliable mode, the round-
trip time, including transmission of a Layer-2 acknowledgment,
is provided:
+ 16-bit MAC addresses, unreliable mode: [1.92 ms, 6.02 ms]
+ 16-bit MAC addresses, reliable mode: [2.46 ms, 6.56 ms]
+ 64-bit MAC addresses, unreliable mode: [2.75 ms, 6.02 ms]
+ 64-bit MAC addresses, reliable mode: [3.30 ms, 6.56 ms]
Latency ranges for the 915 MHz band are as follows:
+ 16-bit MAC addresses, unreliable mode: [5.85 ms, 29.35 ms]
+ 16-bit MAC addresses, reliable mode: [8.35 ms, 31.85 ms]
+ 64-bit MAC addresses, unreliable mode: [8.95 ms, 29.35 ms]
+ 64-bit MAC addresses, reliable mode: [11.45 ms, 31.82 ms]
Latency ranges for the 868 MHz band are as follows:
+ 16-bit MAC addresses, unreliable mode: [11.7 ms, 58.7 ms]
+ 16-bit MAC addresses, reliable mode: [16.7 ms, 63.7 ms]
+ 64-bit MAC addresses, unreliable mode: [17.9 ms, 58.7 ms]
+ 64-bit MAC addresses, reliable mode: [22.9 ms, 63.7 ms]
Note that some of the parameters presented in this section may be
used as link or node evaluation metrics. However, multi-criteria
routing may be too expensive for 6LoWPAN nodes. Rather, various
single-criteria metrics are available and can be selected to suit the
environment or application.
Kim, et al. Informational [Page 12]RFC 6606 6LoWPAN Routing Requirements May 2012
5. 6LoWPAN Routing Requirements
This section defines a list of requirements for 6LoWPAN routing. An
important design property specific to low-power networks is that
LoWPANs have to support multiple device types and roles, such as
o host nodes drawing their power from primary batteries or using
energy harvesting (sometimes called "power-constrained nodes")
o mains-powered host nodes (an example of what we call "power-
affluent nodes")
o power-affluent (but not necessarily mains-powered) high-
performance gateway(s)
o nodes with various functionality (data aggregators, relays, local
manager/coordinators, etc.)
Due to these different device types and roles, LoWPANs need to
consider the following two primary attributes:
o Power conservation: some devices are mains-powered, but many are
battery-operated and need to last several months to a few years
with a single AA battery. Many devices are mains-powered most of
the time but still need to function on batteries for possibly
extended periods (e.g., on a construction site before building
power is switched on for the first time).
o Low performance: tiny devices, small memory sizes, low-performance
processors, low bandwidth, high loss rates, etc.
These fundamental attributes of LoWPANs affect the design of routing
solutions. Whether existing routing specifications are simplified
and modified, or new solutions are introduced in order to fit the
low-power requirements of LoWPANs, they need to meet the requirements
described below.
5.1. Support of 6LoWPAN Device Properties
The general objectives listed in this section should be met by
6LoWPAN routing protocols. The importance of each requirement is
dependent on what node type the protocol is running on and what the
role of the node is. The following requirements consider the
presence of battery-powered nodes in LoWPANs.
Kim, et al. Informational [Page 13]RFC 6606 6LoWPAN Routing Requirements May 2012
[R01] 6LoWPAN routing protocols SHOULD allow implementation with
small code size and require low routing state to fit the typical
6LoWPAN node capacity. Generally speaking, the code size is bounded
by available flash memory size, and the routing table is bounded by
RAM size, possibly limiting it to less than 32 entries.
The RAM size of LoWPAN nodes often ranges between 4 KB and 10 KB
(2 KB minimum), and program flash memory normally consists of 48
KB to 128 KB. (For example, in the current market, MICAz has 128
KB program flash, 4 KB EEPROM, and 512 KB external flash ROM;
TIP700CM has 48 KB program flash, 10 KB RAM, and 1 MB external
flash ROM.)
Due to these hardware restrictions, code SHOULD fit within a small
memory size -- no more than 48 KB to 128 KB of flash memory,
including at least a few tens of KB of application code size. (As
a general observation, a routing protocol of low complexity may
help achieve the goal of reducing power consumption, improves
robustness, requires lower routing state, is easier to analyze,
and may be less prone to security attacks.)
In addition, operation with limited amounts of routing state (such
as routing tables and neighbor lists) SHOULD be maintained, since
some typical memory sizes preclude storing state of a large number
of nodes. For instance, industrial monitoring applications may
need to support a maximum of 20 hops [RFC5673]. Small networks
can be designed to support a smaller number of hops. While the
need for this is highly dependent on the network architecture,
there should be at least one mode of operation that can function
with 32 forwarding entries or less.
[R02] 6LoWPAN routing protocols SHOULD cause minimal power
consumption by efficiently using control packets (e.g., minimizing
expensive IP multicast, which causes link broadcast to the entire
LoWPAN) and by efficiently routing data packets.
One way of optimizing battery lifetime is by achieving a minimal
control message overhead. Compared to such functions as
computational operations or taking sensor samples, radio
communication is by far the dominant factor of power consumption
[Doherty]. Power consumption of transmission and/or reception
depends linearly on the length of data units and on the frequency
of transmission and reception of the data units [Shih].
The energy consumption of two example radio frequency (RF)
controllers for low-power nodes is shown in [Hill]. The TR1000
radio consumes 21 mW when transmitting at 0.75 mW, and 15 mW
during reception (with a receiver sensitivity of -85 dBm). The
Kim, et al. Informational [Page 14]RFC 6606 6LoWPAN Routing Requirements May 2012
CC1000 consumes 31.6 mW when transmitting at 0.75 mW, and 20 mW
during reception (with a receiver sensitivity of -105 dBm). Power
endurance under the concept of an idealized power source is
explained in [Hill]. Based on the energy of an idealized AA
battery, the CC1000 can transmit for approximately 4 days straight
or receive for 9 consecutive days. Note that availability for
reception consumes power as well.
As multicast may cause flooding in the LoWPAN, a 6LoWPAN routing
protocol SHOULD minimize the control cost by multicasting routing
packets.
Control cost of routing protocols in low-power and lossy networks
is discussed in more detail in [ROLL-PROTOCOLS].
5.2. Support of 6LoWPAN Link Properties
6LoWPAN links have the characteristics of low data rate and possibly
high loss rates. The routing requirements described in this section
are derived from the link properties.
[R03] 6LoWPAN routing protocol control messages SHOULD NOT exceed a
single IEEE 802.15.4 frame size, in order to avoid packet
fragmentation and the overhead for reassembly.
In order to save energy, routing overhead should be minimized to
prevent fragmentation of frames. Therefore, 6LoWPAN routing
should not cause packets to exceed the IEEE 802.15.4 frame size.
This reduces the energy required for transmission, avoids
unnecessary waste of bandwidth, and prevents the need for packet
reassembly. The [IEEE802.15.4] standard specifies an MTU of
127 bytes, yielding about 80 octets of actual MAC payload with
security enabled, some of which is taken for the (typically
compressed) IP header [RFC6282]. Avoiding fragmentation at the
adaptation layer may imply the use of semantic fragmentation
and/or algorithms that can work on small increments of routing
information.
[R04] The design of routing protocols for LoWPANs must consider the
fact that packets are to be delivered with sufficient probability
according to application requirements.
Requirements for a successful end-to-end packet delivery ratio
(where delivery may be bounded within certain latency levels)
vary, depending on the application. In industrial applications,
some non-critical monitoring applications may tolerate a
successful delivery ratio of less than 90% with hours of latency;
Kim, et al. Informational [Page 15]RFC 6606 6LoWPAN Routing Requirements May 2012
in some other cases, a delivery ratio of 99.9% is required
[RFC5673]. In building automation applications, application-layer
errors must be below 0.01% [RFC5867].
Successful end-to-end delivery of packets in an IEEE 802.15.4 mesh
depends on the quality of the path selected by the routing
protocol and on the ability of the routing protocol to cope with
short-term and long-term quality variation. The metric of the
routing protocol strongly influences performance of the routing
protocol in terms of delivery ratio.
The quality of a given path depends on the individual qualities of
the links (including the devices) that compose that path.
IEEE 802.15.4 settings affect the quality perceived at upper
layers. In particular, in IEEE 802.15.4 reliable mode, if an
acknowledgment frame is not received after a given period, the
originator retries frame transmission up to a maximum number of
times. If an acknowledgment frame is still not received by the
sender after performing the maximum number of transmission
attempts, the MAC layer assumes that the transmission has failed
and notifies the next higher layer of the failure. Note that
excessive retransmissions may be detrimental; see RFC 3819
[RFC3819].
[R05] The design of routing protocols for LoWPANs must consider the
latency requirements of applications and IEEE 802.15.4 link latency
characteristics.
Latency requirements may differ -- e.g., from a few hundred
milliseconds to minutes -- depending on the type of application.
Real-time building automation applications usually need response
times below 500 ms between egress and ingress, while forced-entry
security alerts must be routed to one or more fixed or mobile user
devices within 5 seconds [RFC5867]. Non-critical closed-loop
applications for industrial automation have latency requirements
that can be as low as 100 ms, but many control loops are tolerant
of latencies above 1 s [RFC5673]. In contrast, urban monitoring
applications allow latencies smaller than the typical intervals
used for reporting sensed information -- for instance, on the
order of seconds to minutes [RFC5548].
The range of latencies of a frame transmission between a single
sender and a single receiver through an ideal unslotted
IEEE 802.15.4 2.4 GHz channel is between 2.46 ms and 6.02 ms with
64-bit MAC addresses in unreliable mode, and between 2.20 ms and
6.56 ms with 64-bit MAC addresses in reliable mode. The range of
latencies of the 868 MHz band is from 11.7 ms to 63.7 ms,
depending on the address type and mode used (reliable or
Kim, et al. Informational [Page 16]RFC 6606 6LoWPAN Routing Requirements May 2012
unreliable). Note that the latencies may be larger than that,
depending on channel load, the MAC-layer settings, and the choice
of reliable or unreliable mode. Note that MAC approaches other
than legacy 802.15.4 may be used (e.g., TDMA). Duty cycling may
further affect latency (see [R08]). Depending on the routing path
chosen and the network diameter, multiple hops may contribute to
the end-to-end latency that an application may experience.
Note that a tradeoff exists between [R05] and [R04].
[R06] 6LoWPAN routing protocols SHOULD be robust to dynamic loss
caused by link failure or device unavailability either in the short
term (approx. 30 ms) -- due to Received Signal Strength Indication
(RSSI) variation, interference variation, noise, and asynchrony -- or
in the long term, due to a depleted power source, hardware breakdown,
operating system misbehavior, etc.
An important trait of 6LoWPAN devices is their unreliability,
which can be due to limited system capabilities and possibly being
closely coupled to the physical world with all its unpredictable
variations. In harsh environments, LoWPANs easily suffer from
link failure. Collisions or link failures easily increase send
and receive queues and can lead to queue overflow and packet
losses.
For home applications, where users expect feedback after carrying
out certain actions (such as handling a remote control while
moving around), routing protocols must converge within 2 seconds
if the destination node of the packet has moved and must converge
within 0.5 seconds if only the sender has moved [RFC5826]. The
tolerance of the recovery time can vary, depending on the
application; however, the routing protocol must provide the
detection of short-term unavailability and long-term
disappearance. The routing protocol has to exploit network
resources (e.g., path redundancy) to offer good network behavior
despite node failure.
Different routing protocols may exhibit different scaling
characteristics with respect to the recovery/convergence time and
the computational resources to achieve recovery after a
convergence; see also [R01] and [R10].
Kim, et al. Informational [Page 17]RFC 6606 6LoWPAN Routing Requirements May 2012
[R07] 6LoWPAN routing protocols SHOULD be designed to correctly
operate in the presence of link asymmetry.
Link asymmetry occurs when the probability of successful
transmission between two nodes is significantly higher in one
direction than in the other. This phenomenon has been reported in
a large number of experimental studies, and it is expected that
6LoWPANs will exhibit link asymmetry.
5.3. Support of 6LoWPAN Characteristics
6LoWPANs can be deployed in different sizes and topologies, adhere to
various models of mobility, be exposed to various levels of
interference, etc. In any case, LoWPANs must maintain low energy
consumption. The requirements described in this subsection are
derived from the network attributes of 6LoWPANs.
[R08] The design of 6LoWPAN routing protocols SHOULD take into
account that some nodes may be unresponsive during certain time
intervals, due to periodic hibernation.
Many nodes in LoWPAN environments might periodically hibernate
(i.e., disable their transceiver activity) in order to save
energy. Therefore, routing protocols must ensure robust packet
delivery despite nodes frequently shutting off their radio
transmission interface. Feedback from the lower IEEE 802.15.4
layer may be considered to enhance the power awareness of 6LoWPAN
routing protocols.
CC1000-based nodes must operate at a duty cycle of approximately
2% to survive for one year from an idealized AA battery power
source [Hill]. For home automation purposes, it is suggested that
the devices have to maximize the sleep phase with a duty cycle
lower than 1% [RFC5826], while in building automation
applications, batteries must be operational for at least 5 years
when the sensing devices are transmitting data (e.g., 64 bytes)
once per minute [RFC5867].
Depending on the application in use, packet rates may range from
one per second to one per day, or beyond. Routing protocols may
take advantage of knowledge about the packet transmission rate and
utilize this information in calculating routing paths. In many
IEEE 802.15.4 deployments, and in other wireless low-power
technologies, forwarders are mains-powered devices (and hence do
not need to sleep). However, it cannot be assumed that all
forwarders are mains-powered. A routing protocol that addresses
this case SHOULD provide a mode in which power consumption is a
metric. In addition, using nodes in power-saving modes for
Kim, et al. Informational [Page 18]RFC 6606 6LoWPAN Routing Requirements May 2012
forwarding may increase delay and reduce the probability of packet
delivery, which in this case also should be available as an input
into the path computation.
[R09] The metric used by 6LoWPAN routing protocols SHOULD provide
some flexibility with respect to the inputs provided by the lower
layers and other measures to optimize path selection, considering
energy balance and link qualities.
In homes, buildings, or infrastructure, some nodes will be
installed with mains power. Such power-installed nodes MUST be
considered as relay points for a prominent role in packet
delivery. 6LoWPAN routing protocols MUST know the power
constraints of the nodes.
Simple hop-count-only mechanisms may be inefficient in 6LoWPANs.
There is a Link Quality Indication (LQI) and/or RSSI from
IEEE 802.15.4 that may be taken into account for better metrics.
The metric to be used (and its goal) may depend on applications
and requirements.
The numbers in Figure 4 represent the Link Delivery Ratio (LDR) of
each pair of nodes. There are studies that show a piecewise
linear dependence between the LQI and the LDR [Chen].
0.6
A-------C
\ /
0.9 \ / 0.9
\ /
B
Figure 4: An Example Network
In this simple example, there are two options in routing from
node A to node C, with the following features:
A. Path AC:
+ (1/0.6) = 1.67 avg. transmissions needed for each packet
(confirmed link-layer delivery with retransmissions and
negligible ACK loss have been assumed)
+ one-hop path
Kim, et al. Informational [Page 19]RFC 6606 6LoWPAN Routing Requirements May 2012
+ good energy consumption and end-to-end latency of data
packets, poor delivery ratio (0.6)
+ poor probability of route reconfigurations
B. Path ABC:
+ (1/0.9)+(1/0.9) = 2.22 avg. transmissions needed for each
packet (under the same assumptions as above)
+ two-hop path
+ poor energy consumption and end-to-end latency of data
packets, good delivery ratio (0.81)
If energy consumption of the network must be minimized, path AC is
the best (this path would be chosen based on a hop-count metric).
However, if the delivery ratio in that case is not sufficient, the
best path is ABC (it would be chosen by an LQI-based metric).
Combinations of both metrics can be used.
The metric also affects the probability of route reconfiguration.
Route reconfiguration, which may be triggered by packet losses,
may require transmission of routing protocol messages. It is
possible to use a metric aimed at selecting the path with a low
route reconfiguration rate by using the LQI as an input to the
metric. Such a path has good properties, including stability and
low control message overhead.
Note that a tradeoff exists between [R09] and [R01].
[R10] 6LoWPAN routing protocols SHOULD be designed to achieve both
scalability -- from a few nodes to maybe millions of nodes -- and
minimal use of system resources.
A LoWPAN may consist of just a couple of nodes (for instance, in a
body-area network), but may also contain much higher numbers of
devices (e.g., monitoring of a city infrastructure or a highway).
For home automation applications, it is envisioned that the
routing protocol must support 250 devices in the network
[RFC5826], while routing protocols for metropolitan-scale sensor
networks must be capable of clustering a large number of sensing
nodes into regions containing on the order of 10^2 to 10^4 sensing
nodes each [RFC5548]. It is therefore necessary that routing
mechanisms are designed to be scalable for operation in networks
of various sizes. However, due to a lack of memory size and
computational power, 6LoWPAN routing might limit forwarding
entries to a small number, such as a maximum of 32 routing table
Kim, et al. Informational [Page 20]RFC 6606 6LoWPAN Routing Requirements May 2012
entries. Particularly in large networks, the routing mechanism
MUST be designed in such a way that the number of routers is
smaller than the number of hosts.
[R11] The procedure of route repair and related control messages
SHOULD NOT harm overall energy consumption from the routing
protocols.
Local repair improves throughput and end-to-end latency,
especially in large networks. Since routes are repaired quickly,
fewer data packets are dropped, and a smaller number of routing
protocol packet transmissions are needed, since routes can be
repaired without source-initiated route discovery [Lee]. One
important consideration here may be to avoid premature energy
depletion, even if that impairs other requirements.
[R12] 6LoWPAN routing protocols SHOULD allow for dynamically adaptive
topologies and mobile nodes. When supporting dynamic topologies and
mobile nodes, route maintenance should keep in mind the goal of a
minimal routing state and routing protocol message overhead.
Topological node mobility may be the result of physical movement
and/or a changing radio environment, making it very likely that
mobility needs to be handled even in a network with physically
static nodes. 6LoWPANs do not make use of a separate protocol to
maintain connectivity to moving nodes but expects the routing
protocol to handle it.
In addition, some nodes may move from one 6LoWPAN to another and
are expected to become functional members of the latter 6LoWPAN in
a limited amount of time.
Building monitoring applications, for instance, have a number of
requirements with respect to recovery and settling time for
mobility that range between 5 and 20 seconds (Section 5.3.1 of
[RFC5867]). For more interactive applications such as those used
in home automation systems, where users provide input and expect
instant feedback, mobility requirements are also stricter and, for
moves within a network, a convergence time below 0.5 seconds is
commonly required (Section 3.2 of [RFC5826]). In industrial
environments, where mobile equipment (e.g., cranes) moves around,
the routing protocol needs to support vehicular speeds of up to
35 km/h [RFC5673]. Currently, 6LoWPANs are not normally being
used for such fast mobility, but dynamic association and
disassociation MUST be supported in 6LoWPANs.
Kim, et al. Informational [Page 21]RFC 6606 6LoWPAN Routing Requirements May 2012
There are several challenges that should be addressed by a 6LoWPAN
routing protocol in order to create robust routing in dynamic
environments:
* Mobile Nodes Changing Their Location inside a LoWPAN:
If the nodes' movement pattern is unknown, mobility cannot
easily be detected or distinguished by the routing protocols.
Mobile nodes can be treated as nodes that disappear and
reappear in another place. The tracking of movement patterns
increases complexity and can be avoided by handling moving
nodes using reactive route updates.
* Movement of a LoWPAN with Respect to Other (Inter)Connected
LoWPANs:
Within each stub network, (one or more) relatively powerful
gateway nodes (6LBRs) need to be configured to handle moving
LoWPANs.
* Nodes Permanently Joining or Leaving the LoWPAN:
In order to ease routing table updates, reduce the size of
these updates, and minimize error control messages, nodes
leaving the network may announce their disassociation to the
closest edge router or to a specific node (if any) that takes
charge of local association and disassociation.
[R13] A 6LoWPAN routing protocol SHOULD support various traffic
patterns -- point-to-point, point-to-multipoint, and multipoint-to-
point -- while avoiding excessive multicast traffic in a LoWPAN.
6LoWPANs often have point-to-multipoint or multipoint-to-point
traffic patterns. Many emerging applications include point-to-
point communication as well. 6LoWPAN routing protocols should be
designed with the consideration of forwarding packets from/to
multiple sources/destinations. Current documents of the ROLL WG
explain that the workload or traffic pattern of use cases for
LoWPANs tends to be highly structured, unlike the any-to-any data
transfers that dominate typical client and server workloads. In
many cases, exploiting such structure may simplify difficult
problems arising from resource constraints or variation in
connectivity.
5.4. Support of Security
The routing requirement described in this subsection allows secure
transmission of routing messages. As in traditional networks,
routing mechanisms in 6LoWPANs present another window from which an
attacker might disrupt and significantly degrade the overall
performance of the 6LoWPAN. Attacks against non-secure routing aim
Kim, et al. Informational [Page 22]RFC 6606 6LoWPAN Routing Requirements May 2012
mainly to contaminate WPANs with false routing information, resulting
in routing inconsistencies. A malicious node can also snoop packets
and then launch replay attacks on the 6LoWPAN nodes. These attacks
can cause harm, especially when the attacker is a high-power device,
such as a laptop. It can also easily drain the batteries of 6LoWPAN
devices by sending broadcast messages, redirecting routes, etc.
[R14] 6LoWPAN routing protocols MUST support confidentiality,
authentication, and integrity services as required for secure
delivery of control messages.
A general set of requirements that may apply to these services can
be found in [KARP-THREATS].
Security is very important for designing robust routing protocols,
but it should not cause significant transmission overhead. The
security aspect, however, seems to be a bit of a tradeoff in a
6LoWPAN, since security is always a costly function. A 6LoWPAN
poses unique challenges to which traditional security techniques
cannot be applied directly. For example, public key cryptography
primitives are typically avoided (as being too expensive), as are
relatively heavyweight conventional encryption methods.
Consequently, it becomes questionable whether the 6LoWPAN devices
can support IPsec as it is. While [RFC6434] makes support of the
IPsec architecture a SHOULD for all IPv6 nodes, considering the
power constraints and limited processing capabilities of
IEEE 802.15.4-capable devices, IPsec is computationally expensive.
Internet Key Exchange (IKEv2) messaging as described in RFC 5996
[RFC5996] will not work well in 6LoWPANs, as we want to minimize
the amount of signaling in these networks. IPsec supports the
Authentication Header (AH) for authenticating the IP header and
the Encapsulating Security Payload (ESP) for authenticating and
encrypting the payload. The main issues of using IPsec are
two-fold: (1) processing power and (2) key management. Since
these tiny 6LoWPAN devices do not process huge amounts of data or
communicate with many different nodes, whether complete
implementation of a Security Association Database (SAD), policy
database, and dynamic key-management protocol are appropriate for
these small battery-powered devices or not is not well understood.
Bandwidth is a very scarce resource in 6LoWPAN environments. The
fact that IPsec additionally requires another header (AH or ESP)
in every packet makes its use problematic in 6LoWPAN environments.
IPsec requires two communicating peers to share a secret key that
is typically established dynamically with IKEv2. Thus, it has an
additional packet overhead incurred by the exchange of IKEv2
packets.
Kim, et al. Informational [Page 23]RFC 6606 6LoWPAN Routing Requirements May 2012
Given existing constraints in 6LoWPAN environments, IPsec may not
be suitable for use in such environments, especially since a
6LoWPAN node may not be capable of operating all IPsec algorithms
on its own. Thus, a 6LoWPAN may need to define its own keying
management method(s) that require minimum overhead in packet size
and in the number of signaling messages that are exchanged. IPsec
will provide authentication and confidentiality between end-nodes
and across multiple LoWPAN links, and may be useful only when two
nodes want to apply security to all exchanged messages. However,
in most cases, the security may be requested at the application
layer as needed, while other messages can flow in the network
without security overhead.
Security threats within LoWPANs may be different from existing
threat models in ad hoc network environments. If IEEE 802.15.4
security is not used, Neighbor Discovery (ND) in IEEE 802.15.4
links is susceptible to threats. These include Neighbor
Solicitation/Neighbor Advertisement (NS/NA) spoofing, a malicious
router, a default router that is "killed", a good router that goes
bad, a spoofed redirect, replay attacks, and remote ND DoS
[RFC3756]. However, if IEEE 802.15.4 security is used, no other
protection is needed for ND, as long as none of the nodes become
compromised, because the Corporate Intranet Model of RFC 3756 can
be assumed [6LoWPAN-ND].
Bootstrapping may also impose additional threats. For example, a
malicious node can obtain initial configuration information in
order to appear as a legitimate node and then carry out various
types of attacks. Such a node can also keep legitimate nodes busy
by broadcasting authentication/join requests. One option for
mitigating such threats is the use of mutual authentication
schemes based on the use of pre-shared keys [Ikram].
The IEEE 802.15.4 MAC provides an AES-based security mechanism.
Routing protocols may define how this mechanism (in conjunction
with IPsec whenever available) can be used to obtain the intended
security, either for the routing protocol alone or in conjunction
with the security used for the data. Byte overhead of the
mechanism, which depends on the security services selected, must
be considered. In the worst case in terms of overhead, the
mechanism consumes 21 bytes of MAC payload.
The IEEE 802.15.4 MAC security is typically supported by crypto
hardware, even in very simple chips that will be used in a
6LoWPAN. Even if the IEEE 802.15.4 MAC security mechanisms are
not used, this crypto hardware is usually available for use by
Kim, et al. Informational [Page 24]RFC 6606 6LoWPAN Routing Requirements May 2012
application code running on these chips. A security protocol
outside IEEE 802.15.4 MAC security SHOULD therefore provide a mode
of operation that is covered by this crypto hardware.
IEEE 802.15.4 does not specify protection for acknowledgment
frames. Since the sequence numbers of data frames are sent in the
clear, an adversary can forge an acknowledgment for each data
frame. Exploitation of this weakness can be combined with
targeted jamming to prevent delivery of selected packets.
Consequently, IEEE 802.15.4 acknowledgments cannot be relied upon.
In applications that require high security, the routing protocol
must not exploit feedback from acknowledgments (e.g., to keep
track of neighbor connectivity, see [R16]).
5.5. Support of Mesh-Under Forwarding
One LoWPAN may be built as one IPv6 link. In this case, mesh-under
forwarding mechanisms must be supported. While this document
provides general, layer-agnostic guidelines about the design of
6LoWPAN routing, the requirements in this section are specifically
related to Layer 2. These requirements are directed to bodies that
might consider working on mesh-under routing, such as the IEEE. The
requirements described in this subsection allow optimization and
correct operation of routing solutions, taking into account the
specific features of the mesh-under configuration.
[R15] Mesh-under requires the development of a routing protocol
operating below IP. This protocol MUST support 16-bit short and
64-bit extended MAC addresses.
[R16] In order to perform discovery and maintenance of neighbors
(i.e., neighborhood discovery as opposed to ND-style neighbor
discovery), LoWPAN nodes SHOULD avoid sending separate "Hello"
messages. Instead, link-layer mechanisms (such as acknowledgments)
MAY be utilized to keep track of active neighbors.
Reception of an acknowledgment after a frame transmission may
render unnecessary the transmission of explicit Hello messages,
for example. In a more general view, any frame received by a node
may be used as an input to evaluate the connectivity between the
sender and receiver of that frame.
[R17] If the routing protocol functionality includes enabling IP
multicast, then it MAY employ structure in the network for efficient
distribution in order to minimize link-layer broadcast.
Kim, et al. Informational [Page 25]RFC 6606 6LoWPAN Routing Requirements May 2012
5.6. Support of Management
When a new protocol is designed, the operational environment and
manageability of the protocol should be considered from the start
[RFC5706]. This subsection provides a requirement for the
manageability of 6LoWPAN routing protocols.
[R18] A 6LoWPAN routing protocol SHOULD be designed according to the
guidelines for operations and management stated in [RFC5706].
The management operations that a 6LoWPAN routing protocol
implementation can support depend on the memory and processing
capabilities of the 6LoWPAN devices used, which are typically
constrained. However, 6LoWPANs may benefit significantly from
supporting such 6LoWPAN routing protocol management operations as
configuration and performance monitoring.
The design of 6LoWPAN routing protocols should take into account
that, according to "Architectural Principles of the Internet"
[RFC1958], "options and parameters should be configured or
negotiated dynamically rather than manually". This is especially
important for 6LoWPANs, which can be composed of a large number of
devices (and, in addition, these devices may not have an
appropriate user interface). Therefore, parameter
autoconfiguration is a desirable property for a 6LoWPAN routing
protocol, although some subset of routing protocol parameters may
allow other forms of configuration as well.
In order to verify the correct operation of the 6LoWPAN routing
protocol and the network itself, a 6LoWPAN routing protocol should
allow monitoring of the status and/or value of 6LoWPAN routing
protocol parameters and data structures such as routing table
entries. In order to enable fault management, further monitoring
of the 6LoWPAN routing protocol operation is needed. For this,
faults can be reported via error log messages. These messages may
contain information such as the number of times a packet could not
be sent to a valid next hop, the duration of each period without
connectivity, memory overflow and its causes, etc.
[RFC5706] -- in particular its Section 3 -- provides a
comprehensive guide to properly designing the management solution
for a 6LoWPAN routing protocol.
Kim, et al. Informational [Page 26]RFC 6606 6LoWPAN Routing Requirements May 2012
6. Security Considerations
Security issues are described in Section 5.4. The security
considerations in RFC 4919 [RFC4919], RFC 4944 [RFC4944], and
RFC 4593 [RFC4593] apply as well.
The use of wireless links renders a 6LoWPAN susceptible to attacks
like any other wireless network. In outdoor 6LoWPANs, the physical
exposure of the nodes allows an adversary to capture, clone, or
tamper with these devices. In ad hoc 6LoWPANs that are dynamic in
both their topology and node memberships, a static security
configuration does not suffice. Spoofed, altered, or replayed
routing information might occur, while multihopping could delay the
detection and treatment of attacks.
This specification expects that the link layer is sufficiently
protected, either by means of physical or IP security for the
backbone link, or with MAC-sublayer cryptography. However, link-
layer encryption and authentication may not be sufficient to provide
confidentiality, authentication, integrity, and freshness to both
data and routing protocol packets. Time synchronization, self-
organization, and secure localization for multi-hop routing are also
critical to support.
For secure routing protocol operation, it may be necessary to
consider authenticated broadcast (and multicast) and bidirectional
link verification. On the other hand, secure end-to-end data
delivery can be assisted by the routing protocol. For example,
multi-path routing could be considered for increasing security to
prevent selective forwarding. However, the challenge is that
6LoWPANs already have high resource constraints, so that 6LBR and
LoWPAN nodes may require different security solutions.
7. Acknowledgments
The authors of this document highly appreciate the authors of "IPv6
over Low Power WPAN Security Analysis" [6LoWPAN-SEC]. Although their
security analysis work is not ongoing at the time of this writing,
the valuable information and text in that document are used in
Section 5.4 of this document, per advice received during IESG review
procedures. Thanks to their work, Section 5.4 is much improved. The
authors also thank S. Chakrabarti, who gave valuable comments
regarding mesh-under requirements, and A. Petrescu for significant
review.
Carles Gomez has been supported in part by FEDER and by the Spanish
Government through projects TIC2006-04504 and TEC2009-11453.
Kim, et al. Informational [Page 27]
RFC 6606 6LoWPAN Routing Requirements May 2012
8. References
8.1. Normative References
[IEEE802.15.4]
IEEE Computer Society, "IEEE Standard for Local and
Metropolitan Area Networks -- Part 15.4: Low-Rate
Wireless Personal Area Networks (LR-WPANs)", IEEE
Std. 802.15.4-2011, September 2011.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3756] Nikander, P., Ed., Kempf, J., and E. Nordmark, "IPv6
Neighbor Discovery (ND) Trust Models and Threats",
RFC 3756, May 2004.
[RFC3819] Karn, P., Ed., Bormann, C., Fairhurst, G., Grossman, D.,
Ludwig, R., Mahdavi, J., Montenegro, G., Touch, J., and L.
Wood, "Advice for Internet Subnetwork Designers", BCP 89,
RFC 3819, July 2004.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, August 2007.
[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, September 2007.
[RFC5548] Dohler, M., Ed., Watteyne, T., Ed., Winter, T., Ed., and
D. Barthel, Ed., "Routing Requirements for Urban Low-Power
and Lossy Networks", RFC 5548, May 2009.
[RFC5673] Pister, K., Ed., Thubert, P., Ed., Dwars, S., and T.
Phinney, "Industrial Routing Requirements in Low-Power and
Lossy Networks", RFC 5673, October 2009.
Kim, et al. Informational [Page 28]RFC 6606 6LoWPAN Routing Requirements May 2012
8.2. Informative References
[6LoWPAN-ND]
Shelby, Z., Ed., Chakrabarti, S., and E. Nordmark,
"Neighbor Discovery Optimization for Low Power and Lossy
Networks (6LoWPAN)", Work in Progress, October 2011.
[6LoWPAN-SEC]
Park, S., Kim, K., Haddad, W., Ed., Chakrabarti, S., and
J. Laganier, "IPv6 over Low Power WPAN Security Analysis",
Work in Progress, March 2011.
[Bulusu] Bulusu, N., Ed., and S. Jha, Ed., "Wireless Sensor
Networks: A Systems Perspective", Artech House,
ISBN 9781580538671, July 2005.
[Chen] Chen, B., Muniswamy-Reddy, K., and M. Welsh, "Ad-Hoc
Multicast Routing on Resource-Limited Sensor Nodes", Proc.
2nd International Workshop on Multi-hop Ad Hoc Networks,
May 2006.
[Doherty] Doherty, L., Warneke, B., Boser, B., and K. Pister,
"Energy and Performance Considerations for Smart Dust",
International Journal of Parallel and Distributed Systems
and Networks, Vol. 4, No. 3, 2001.
[Hill] Hill, J., "System Architecture for Wireless Sensor
Networks", Ph.D. Thesis, UC Berkeley, 2003.
[Ikram] Ikram, M., Chowdhury, A., Zafar, B., Cha, H., Kim, K.,
Yoo, S., and D. Kim, "A Simple Lightweight Authentic
Bootstrapping Protocol for IPv6-based Low Rate Wireless
Personal Area Networks (6LoWPANs)", Proc. International
Conference on Wireless Communications and
Mobile Computing, June 2009.
[KARP-THREATS]
Lebovitz, G. and M. Bhatia, "Keying and Authentication for
Routing Protocols (KARP) Overview, Threats, and
Requirements", Work in Progress, May 2012.
[Kuhn] Kuhn, F., Wattenhofer, R., and A. Zollinger, "Worst-Case
Optimal and Average-Case Efficient Ad-Hoc Geometric
Routing", MobiHoc '03: Proceedings of the 4th ACM
International Symposium on Mobile Ad Hoc Networking and
Computing, June 2003.
Kim, et al. Informational [Page 29]RFC 6606 6LoWPAN Routing Requirements May 2012
[Latre] Latre, B., De Mil, P., Moerman, I., Dhoedt, B., and P.
Demeester, "Throughput and Delay Analysis of Unslotted
IEEE 802.15.4", Journal of Networks, Vol. 1, No. 1,
May 2006.
[Lee] Lee, S., Belding-Royer, E., and C. Perkins, "Scalability
Study of the Ad Hoc On-Demand Distance-Vector Routing
Protocol", International Journal of Network Management,
Vol. 13, pp. 97-114, March 2003.
[RFC1958] Carpenter, B., Ed., "Architectural Principles of the
Internet", RFC 1958, June 1996.
[RFC5556] Touch, J. and R. Perlman, "Transparent Interconnection of
Lots of Links (TRILL): Problem and Applicability
Statement", RFC 5556, May 2009.
[RFC5706] Harrington, D., "Guidelines for Considering Operations and
Management of New Protocols and Protocol Extensions",
RFC 5706, November 2009.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks",
RFC 5826, April 2010.
[RFC5867] Martocci, J., Ed., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6282] Hui, J., Ed., and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
September 2011.
[RFC6434] Jankiewicz, E., Loughney, J., and T. Narten, "IPv6 Node
Requirements", RFC 6434, December 2011.
[ROLL-PROTOCOLS]
Levis, P., Tavakoli, A., and S. Dawson-Haggerty, "Overview
of Existing Routing Protocols for Low Power and Lossy
Networks", Work in Progress, April 2009.
Kim, et al. Informational [Page 30]RFC 6606 6LoWPAN Routing Requirements May 2012
[Shih] Shih, E., Cho, S., Ickes, N., Min, R., Sinha, A., Wang,
A., and A. Chandrakasan, "Physical Layer Driven Protocols
and Algorithm Design for Energy-Efficient Wireless Sensor
Networks", MobiCom '01: Proceedings of the 7th ACM Annual
International Conference on Mobile Computing and
Networking, July 2001.
[Watteyne] Watteyne, T., Molinaro, A., Richichi, M., and M. Dohler,
"From MANET To IETF ROLL Standardization: A Paradigm Shift
in WSN Routing Protocols", IEEE Communications Surveys and
Tutorials, Vol. 13, Issue 4, pp. 688-707, 2011,
<http://ieeexplore.ieee.org/xpl/
articleDetails.jsp?arnumber=5581105>.
Kim, et al. Informational [Page 31]RFC 6606 6LoWPAN Routing Requirements May 2012
Authors' Addresses
Eunsook Eunah Kim
ETRI
161 Gajeong-dong
Yuseong-gu
Daejeon 305-700
Korea
Phone: +82-42-860-6124
EMail: eunah.ietf@gmail.com
Dominik Kaspar
Simula Research Laboratory
Martin Linges v 17
Fornebu 1364
Norway
Phone: +47-6782-8223
EMail: dokaspar.ietf@gmail.com
Carles Gomez
Universitat Politecnica de Catalunya/Fundacio i2CAT
Escola d'Enginyeria de Telecomunicacio i Aeroespacial
de Castelldefels
C/Esteve Terradas, 7
Castelldefels 08860
Spain
Phone: +34-93-413-7206
EMail: carlesgo@entel.upc.edu
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
EMail: cabo@tzi.org
Kim, et al. Informational [Page 32]
