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Updates:
Keywords: RPL Option, 6LoWPAN, RFC 6553
Internet Engineering Task Force (IETF) M.I. Robles
Request for Comments: 9008 UTN-FRM/Aalto
Updates: 6550, 6553, 8138 M. Richardson
Category: Standards Track SSW
ISSN: 2070-1721 P. Thubert
Cisco
April 2021
Using RPI Option Type, Routing Header for Source Routes, and IPv6-in-
IPv6 Encapsulation in the RPL Data Plane
Abstract
This document looks at different data flows through Low-Power and
Lossy Networks (LLN) where RPL (IPv6 Routing Protocol for Low-Power
and Lossy Networks) is used to establish routing. The document
enumerates the cases where RPL Packet Information (RPI) Option Type
(RFC 6553), RPL Source Route Header (RFC 6554), and IPv6-in-IPv6
encapsulation are required in the data plane. This analysis provides
the basis upon which to design efficient compression of these
headers. This document updates RFC 6553 by adding a change to the
RPI Option Type. Additionally, this document updates RFC 6550 by
defining a flag in the DODAG Information Object (DIO) Configuration
option to indicate this change and updates RFC 8138 as well to
consider the new Option Type when the RPL Option is decompressed.
Status of This Memo
This is an Internet Standards Track document.
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). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9008.
Copyright Notice
Copyright (c) 2021 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
(https://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. Introduction
1.1. Overview
2. Terminology and Requirements Language
3. RPL Overview
4. Updates to RFC 6550, RFC 6553, and RFC 8138
4.1. Updates to RFC 6550
4.1.1. Advertising External Routes with Non-Storing Mode
Signaling
4.1.2. Configuration Options and Mode of Operation
4.1.3. Indicating the New RPI in the DODAG Configuration
Option Flag
4.2. Updates to RFC 6553: Indicating the New RPI Option Type
4.3. Updates to RFC 8138: Indicating the Way to Decompress with
the New RPI Option Type
5. Reference Topology
6. Use Cases
7. Storing Mode
7.1. Storing Mode: Interaction between Leaf and Root
7.1.1. SM: Example of Flow from RAL to Root
7.1.2. SM: Example of Flow from Root to RAL
7.1.3. SM: Example of Flow from Root to RUL
7.1.4. SM: Example of Flow from RUL to Root
7.2. SM: Interaction between Leaf and Internet
7.2.1. SM: Example of Flow from RAL to Internet
7.2.2. SM: Example of Flow from Internet to RAL
7.2.3. SM: Example of Flow from RUL to Internet
7.2.4. SM: Example of Flow from Internet to RUL
7.3. SM: Interaction between Leaf and Leaf
7.3.1. SM: Example of Flow from RAL to RAL
7.3.2. SM: Example of Flow from RAL to RUL
7.3.3. SM: Example of Flow from RUL to RAL
7.3.4. SM: Example of Flow from RUL to RUL
8. Non-Storing Mode
8.1. Non-Storing Mode: Interaction between Leaf and Root
8.1.1. Non-SM: Example of Flow from RAL to Root
8.1.2. Non-SM: Example of Flow from Root to RAL
8.1.3. Non-SM: Example of Flow from Root to RUL
8.1.4. Non-SM: Example of Flow from RUL to Root
8.2. Non-Storing Mode: Interaction between Leaf and Internet
8.2.1. Non-SM: Example of Flow from RAL to Internet
8.2.2. Non-SM: Example of Flow from Internet to RAL
8.2.3. Non-SM: Example of Flow from RUL to Internet
8.2.4. Non-SM: Example of Flow from Internet to RUL
8.3. Non-SM: Interaction between Leaves
8.3.1. Non-SM: Example of Flow from RAL to RAL
8.3.2. Non-SM: Example of Flow from RAL to RUL
8.3.3. Non-SM: Example of Flow from RUL to RAL
8.3.4. Non-SM: Example of Flow from RUL to RUL
9. Operational Considerations of Supporting RULs
10. Operational Considerations of Introducing 0x23
11. IANA Considerations
11.1. Option Type in RPL Option
11.2. Change to the "DODAG Configuration Option Flags"
Subregistry
11.3. Change MOP Value 7 to Reserved
12. Security Considerations
13. References
13.1. Normative References
13.2. Informative References
Acknowledgments
Authors' Addresses
1. Introduction
RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
[RFC6550] is a routing protocol for constrained networks. [RFC6553]
defines the RPL Option carried within the IPv6 Hop-by-Hop Options
header to carry the RPLInstanceID and quickly identify
inconsistencies (loops) in the routing topology. The RPL Option is
commonly referred to as the RPL Packet Information (RPI), although
the RPI is the routing information that is defined in [RFC6550] and
transported in the RPL Option. RFC 6554 [RFC6554] defines the "RPL
Source Route Header" (RH3), an IPv6 extension header to deliver
datagrams within a RPL routing domain, particularly in Non-Storing
mode.
These various items are referred to as RPL artifacts, and they are
seen on all of the data plane traffic that occurs in RPL-routed
networks; they do not, in general, appear on the RPL control plane at
all, which is mostly hop-by-hop traffic (one exception being
Destination Advertisement Object (DAO) messages in Non-Storing mode).
It has become clear from attempts to do multi-vendor
interoperability, and from a desire to compress as many of the above
artifacts as possible, that not all implementers agree when artifacts
are necessary, or when they can be safely omitted, or removed.
The ROLL (Routing Over Low power and Lossy networks) Working Group
analyzed how IPv6 rules [RFC2460] apply to the Storing and Non-
Storing use of RPL. The result was 24 data-plane use cases. They
are exhaustively outlined here in order to be completely unambiguous.
During the processing of this document, new rules were published as
[RFC8200], and this document was updated to reflect the normative
changes in that document.
This document updates [RFC6553], changing the value of the Option
Type of the RPL Option to make routers compliant with [RFC8200]
ignore this option when it is not recognized.
A Routing Header Dispatch for IPv6 over Low-Power Wireless Personal
Area Networks (6LoWPAN) (6LoRH) [RFC8138] defines a mechanism for
compressing RPL Option information and Routing Header type 3 (RH3)
[RFC6554], as well as an efficient IPv6-in-IPv6 technique.
Most of the use cases described herein require the use of IPv6-in-
IPv6 packet encapsulation. When encapsulating and decapsulating
packets, [RFC6040] MUST be applied to map the setting of the explicit
congestion notification (ECN) field between inner and outer headers.
Additionally, [TUNNELS] is recommended reading to explain the
relationship of IP tunnels to existing protocol layers and the
challenges in supporting IP tunneling.
Unconstrained uses of RPL are not in scope of this document, and
applicability statements for those uses may provide different advice,
e.g., [ACP].
1.1. Overview
The rest of the document is organized as follows: Section 2 describes
the terminology that is used. Section 3 provides a RPL overview.
Section 4 describes the updates to RFC 6553, RFC 6550, and RFC 8138.
Section 5 provides the reference topology used for the use cases.
Section 6 describes the use cases included. Section 7 describes the
Storing mode cases and Section 8 the Non-Storing mode cases.
Section 9 describes the operational considerations of supporting RPL-
unaware leaves. Section 10 depicts operational considerations for
the proposed change on RPI Option Type, Section 11 the IANA
considerations, and then Section 12 describes the security aspects.
2. Terminology and Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
The following terminology defined in [RFC7102] applies to this
document: LLN, RPL, RPL domain, and ROLL.
Consumed: A Routing Header is consumed when the Segments Left field
is zero, which indicates that the destination in the IPv6 header
is the final destination of the packet and that the hops in the
Routing Header have been traversed.
RPL Leaf: An IPv6 host that is attached to a RPL router and obtains
connectivity through a RPL Destination-Oriented Directed Acyclic
Graph (DODAG). As an IPv6 node, a RPL leaf is expected to ignore
a consumed Routing Header, and as an IPv6 host, it is expected to
ignore a Hop-by-Hop Options header. Thus, a RPL leaf can
correctly receive a packet with RPL artifacts. On the other hand,
a RPL leaf is not expected to generate RPL artifacts or to support
IP-in-IP encapsulation. For simplification, this document uses
the standalone term leaf to mean a RPL leaf.
RPL Packet Information (RPI): The information defined abstractly in
[RFC6550] to be placed in IP packets. The term is commonly used,
including in this document, to refer to the RPL Option [RFC6553]
that transports that abstract information in an IPv6 Hop-by-Hop
Options header. [RFC8138] provides an alternate (more compressed)
formatting for the same abstract information.
RPL-Aware Node (RAN): A device that implements RPL. Please note
that the device can be found inside the LLN or outside LLN.
RPL-Aware Leaf (RAL): A RPL-aware node that is also a RPL leaf.
RPL-Unaware Node: A device that does not implement RPL, thus the
device is RPL unaware. Please note that the device can be found
inside the LLN.
RPL-Unaware Leaf (RUL): A RPL-unaware node that is also a RPL leaf.
6LoWPAN Node (6LN): [RFC6775] defines it as the following: "A
6LoWPAN node is any host or router participating in a LoWPAN.
This term is used when referring to situations in which either a
host or router can play the role described." In this document, a
6LN acts as a leaf.
6LoWPAN Router (6LR): [RFC6775] defines it as the following: "An
intermediate router in the LoWPAN that is able to send and receive
Router Advertisements (RAs) and Router Solicitations (RSs) as well
as forward and route IPv6 packets. 6LoWPAN routers are present
only in route-over topologies."
6LoWPAN Border Router (6LBR): [RFC6775] defines it as the following:
"A border router located at the junction of separate 6LoWPAN
networks or between a 6LoWPAN network and another IP network.
There may be one or more 6LBRs at the 6LoWPAN network boundary. A
6LBR is the responsible authority for IPv6 prefix propagation for
the 6LoWPAN network it is serving. An isolated LoWPAN also
contains a 6LBR in the network, which provides the prefix(es) for
the isolated network."
Flag Day: A flag day is caused when a network is reconfigured in a
way that nodes running the older configuration cannot communicate
with nodes running the new configuration. An example of a flag
day is when the ARPANET changed from IP version 3 to IP version 4
on January 1, 1983 [RFC0801]. In the context of this document, a
switch from RPI Option Type (0x63) to Option Type (0x23) presents
as a disruptive changeover. In order to reduce the amount of time
for such a changeover, Section 4.1.3 provides a mechanism to allow
nodes to be incrementally upgraded.
Non-Storing Mode (Non-SM): A RPL mode of operation in which the RPL-
aware nodes send information to the root about their parents.
Thus, the root knows the topology. Because the root knows the
topology, the intermediate 6LRs do not maintain routing state, and
source routing is needed.
Storing Mode (SM): A RPL mode of operation in which RPL-aware nodes
(6LRs) maintain routing state (of the children) so that source
routing is not needed.
| Note: Due to lack of space in some tables, we refer to IPv6-in-
| IPv6 as IP6-IP6.
3. RPL Overview
RPL defines the RPL control message (control plane), which is an
ICMPv6 message [RFC4443] with a Type of 155. DIS (DODAG Information
Solicitation), DIO (DODAG Information Object), and DAO (Destination
Advertisement Object) messages are all RPL control messages but with
different Code values. A RPL stack is shown in Figure 1.
+--------------+
| Upper Layers |
| |
+--------------+
| RPL |
| |
+--------------+
| ICMPv6 |
| |
+--------------+
| IPv6 |
| |
+--------------+
| 6LoWPAN |
| |
+--------------+
| PHY-MAC |
| |
+--------------+
Figure 1: RPL Stack
RPL supports two modes of Downward internal traffic: in Storing mode
(SM), it is fully stateful; in Non-Storing mode (non-SM), it is fully
source routed. A RPL Instance is either fully Storing or fully Non-
Storing, i.e., a RPL Instance with a combination of fully Storing and
Non-Storing nodes is not supported with the current specifications at
the time of writing this document. External routes are advertised
with non-SM messaging even in an SM network, see Section 4.1.1
4. Updates to RFC 6550, RFC 6553, and RFC 8138
4.1. Updates to RFC 6550
4.1.1. Advertising External Routes with Non-Storing Mode Signaling
Section 6.7.8 of [RFC6550] introduces the 'E' flag that is set to
indicate that the 6LR that generates the DAO redistributes external
targets into the RPL network. An external target is a target that
has been learned through an alternate protocol, for instance, a route
to a prefix that is outside the RPL domain but reachable via a 6LR.
Being outside of the RPL domain, a node that is reached via an
external target cannot be guaranteed to ignore the RPL artifacts and
cannot be expected to process the compression defined in [RFC8138]
correctly. This means that the RPL artifacts should be contained in
an IP-in-IP encapsulation that is removed by the 6LR, and that any
remaining compression should be expanded by the 6LR before it
forwards a packet outside the RPL domain.
This specification updates [RFC6550] to say that advertising external
targets using Non-Storing mode DAO messaging even in a Storing mode
network is RECOMMENDED. This way, external routes are not advertised
within the DODAG, and all packets to an external target reach the
root like normal Non-Storing mode traffic. The Non-Storing mode DAO
informs the root of the address of the 6LR that injects the external
route, and the root uses IP-in-IP encapsulation to that 6LR, which
terminates the IP-in-IP tunnel and forwards the original packet
outside the RPL domain free of RPL artifacts.
In the other direction, for traffic coming from an external target
into the LLN, the parent (6LR) that injects the traffic always
encapsulates to the root. This whole operation is transparent to
intermediate routers that only see traffic between the 6LR and the
root, and only the root and the 6LRs that inject external routes in
the network need to be upgraded to add this function to the network.
A RUL is a special case of external target when the target is
actually a host, and it is known to support a consumed Routing Header
and to ignore a Hop-by-Hop Options header as prescribed by [RFC8200].
The target may have been learned through an external routing protocol
or may have been registered to the 6LR using [RFC8505].
In order to enable IP-in-IP all the way to a 6LN, it is beneficial
that the 6LN supports decapsulating IP-in-IP, but that is not assumed
by [RFC8504]. If the 6LN is a RUL, the root that encapsulates a
packet SHOULD terminate the tunnel at a parent 6LR. The root may
encapsulate all the way to the RUL if it is aware that the RUL
supports IP-in-IP decapsulation and the artifacts in the outer header
chain.
A node that is reachable over an external route is not expected to
support [RFC8138]. Whether a decapsulation took place or not and
even when the 6LR is delivering the packet to a RUL, the 6LR that
injected an external route MUST undo the [RFC8138] compression on the
packet before forwarding over that external route.
4.1.2. Configuration Options and Mode of Operation
Section 6.7.6 of [RFC6550] describes the DODAG Configuration option
as containing a series of flags in the first octet of the payload.
Anticipating future work to revise RPL relating to how the LLN and
DODAG are configured, this document renames the IANA "DODAG
Configuration Option Flags" subregistry so that it applies to Mode of
Operation (MOP) values zero (0) through six (6) only, leaving the
flags unassigned for MOP value seven (7). The MOP is described in
[RFC6550], Section 6.3.1.
In addition, this document reserves MOP value 7 for future expansion.
See Sections 11.2 and 11.3.
4.1.3. Indicating the New RPI in the DODAG Configuration Option Flag
In order to avoid a flag day caused by lack of interoperation between
nodes of the new RPI Option Type (0x23) and old RPI Option Type
(0x63), this section defines a flag in the DODAG Configuration
option, to indicate when the new RPI Option Type can be safely used.
This means that the flag is going to indicate the value of Option
Type that the network will be using for the RPL Option. Thus, when a
node joins to a network, it will know which value to use. With this,
RPL-capable nodes know if it is safe to use 0x23 when creating a new
RPL Option. A node that forwards a packet with an RPI MUST NOT
modify the Option Type of the RPL Option.
This is done using a DODAG Configuration option flag that will signal
"RPI 0x23 enable" and propagate through the network. Section 6.3.1
of [RFC6550] defines a 3-bit Mode of Operation (MOP) in the DIO Base
Object. The flag is defined only for MOP value between 0 to 6.
For a MOP value of 7, a node MUST use the RPI 0x23 option.
As stated in [RFC6550], the DODAG Configuration option is present in
DIO messages. The DODAG Configuration option distributes
configuration information. It is generally static, and it does not
change within the DODAG. This information is configured at the DODAG
root and distributed throughout the DODAG with the DODAG
Configuration option. Nodes other than the DODAG root do not modify
this information when propagating the DODAG Configuration option.
Currently, the DODAG Configuration option in [RFC6550] states that
the unused bits "MUST be initialized to zero by the sender and MUST
be ignored by the receiver." If the flag is received with a value
zero, which is the default, then new nodes will remain compatible
with RFC 6553 -- originating traffic with the old RPI Option Type
value (0x63). If the flag is received with a value of 1, then the
value for the RPL Option MUST be set to 0x23.
Bit number three of the Flags field in the DODAG Configuration option
is to be used as shown in Table 1 (which is the same as Table 36 in
Section 11 and is shown here for convenience):
+============+=================+===============+
| Bit number | Description | Reference |
+============+=================+===============+
| 3 | RPI 0x23 enable | This document |
+------------+-----------------+---------------+
Table 1: DODAG Configuration Option Flag to
Indicate the RPI Flag Day
In the case of reboot, the node (6LN or 6LR) does not remember the
RPI Option Type (i.e., whether or not the flag is set), so the node
will not trigger DIO messages until a DIO message is received that
indicates the RPI value to be used. The node will use the value 0x23
if the network supports this feature.
4.2. Updates to RFC 6553: Indicating the New RPI Option Type
This modification is required in order to be able to send, for
example, IPv6 packets from a RPL-aware leaf to a RPL-unaware node
through the Internet (see Section 7.2.1) without requiring IPv6-in-
IPv6 encapsulation.
Section 6 of [RFC6553] states, as shown in Table 2, that in the
Option Type field of the RPL Option, the two high-order bits must be
set to '01' and the third bit is equal to '1'. 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 in route. The remaining bits serve as the
Option Type.
+===========+===================+=============+===========+
| Hex Value | Binary Value | Description | Reference |
| +=====+=====+=======+ | |
| | act | chg | rest | | |
+===========+=====+=====+=======+=============+===========+
| 0x63 | 01 | 1 | 00011 | RPL Option | [RFC6553] |
+-----------+-----+-----+-------+-------------+-----------+
Table 2: Option Type in RPL Option
This document illustrates that it is not always possible to know for
sure at the source whether a packet will travel only within the RPL
domain or whether it will leave it.
At the time [RFC6553] was published, leaking a Hop-by-Hop Options
header in the outer IPv6 header chain could potentially impact core
routers in the Internet. So at that time, it was decided to
encapsulate any packet with a RPL Option using IPv6-in-IPv6 in all
cases where it was unclear whether the packet would remain within the
RPL domain. In the exception case where a packet would still leak,
the Option Type would ensure that the first router in the Internet
that does not recognize the option would drop the packet and protect
the rest of the network.
Even with [RFC8138], where the IPv6-in-IPv6 header is compressed,
this approach yields extra bytes in a packet; this means consuming
more energy and more bandwidth, incurring higher chances of loss, and
possibly causing a fragmentation at the 6LoWPAN level. This impacts
the daily operation of constrained devices for a case that generally
does not happen and would not heavily impact the core anyway.
While the intention was and remains that the Hop-by-Hop Options
header with a RPL Option should be confined within the RPL domain,
this specification modifies this behavior in order to reduce the
dependency on IPv6-in-IPv6 and protect the constrained devices.
Section 4 of [RFC8200] clarifies the behavior of routers in the
Internet as follows: "it is now expected that nodes along a packet's
delivery path only examine and process the Hop-by-Hop Options header
if explicitly configured to do so."
When unclear about the travel of a packet, it becomes preferable for
a source not to encapsulate, accepting the fact that the packet may
leave the RPL domain on its way to its destination. In that event,
the packet should reach its destination and should not be discarded
by the first node that does not recognize the RPL Option. However,
with the current value of the Option Type, if a node in the Internet
is configured to process the Hop-by-Hop Options header, and if such a
node encounters an Option Type with the first two bits set to 01 and
the node conforms to [RFC8200], it will drop the packet. Host
systems should do the same, irrespective of the configuration.
Thus, this document updates the Option Type of the RPL Option
[RFC6553], naming it RPI Option Type for simplicity (Table 3): the
two high order bits MUST be set to '00', and the third bit is equal
to '1'. The first two bits indicate that the IPv6 node MUST skip
over this option and continue processing the header ([RFC8200],
Section 4.2) if it doesn't recognize the Option Type, and the third
bit continues to be set to indicate that the Option Data may change
en route. The rightmost five bits remain at 0x3(00011). This
ensures that a packet that leaves the RPL domain of an LLN (or that
leaves the LLN entirely) will not be discarded when it contains the
RPL Option.
With the new Option Type, if an IPv6 (intermediate) node (RPL
unaware) receives a packet with a RPL Option, it should ignore the
Hop-by-Hop RPL Option (skip over this option and continue processing
the header). This is relevant, as it was mentioned previously, in
the case that there is a flow from RAL to Internet (see
Section 7.2.1).
This is a significant update to [RFC6553].
+===========+===================+=============+===============+
| Hex Value | Binary Value | Description | Reference |
| +=====+=====+=======+ | |
| | act | chg | rest | | |
+===========+=====+=====+=======+=============+===============+
| 0x23 | 00 | 1 | 00011 | RPL Option | This document |
+-----------+-----+-----+-------+-------------+---------------+
Table 3: Revised Option Type in RPL Option
Without the signaling described below, this change would otherwise
create a lack of interoperation (flag day) for existing networks that
are currently using 0x63 as the RPI Option Type value. A move to
0x23 will not be understood by those networks. It is suggested that
RPL implementations accept both 0x63 and 0x23 when processing the
header.
When forwarding packets, implementations SHOULD use the same value of
RPI Type as was received. This is required because the RPI Option
Type does not change en route ([RFC8200], Section 4.2). It allows
the network to be incrementally upgraded and allows the DODAG root to
know which parts of the network have been upgraded.
When originating new packets, implementations should have an option
to determine which value to originate with. This option is
controlled by the DODAG Configuration option (Section 4.1.3).
The change of RPI Option Type from 0x63 to 0x23 makes all nodes that
are compliant with Section 4.2 of [RFC8200] tolerant of the RPL
artifacts. There is no longer a need to remove the artifacts when
sending traffic to the Internet. This change clarifies when to use
IPv6-in-IPv6 headers and how to address them: the Hop-by-Hop Options
header containing the RPI MUST always be added when 6LRs originate
packets (without IPv6-in-IPv6 headers), and IPv6-in-IPv6 headers MUST
always be added when a 6LR finds that it needs to insert a Hop-by-Hop
Options header containing the RPL Option. The IPv6-in-IPv6 header is
to be addressed to the RPL root when on the way up, and to the end
host when on the way down.
In the Non-Storing case, dealing with RPL-unaware leaf nodes is much
easier as the 6LBR (DODAG root) has complete knowledge about the
connectivity of all DODAG nodes, and all traffic flows through the
root node.
The 6LBR can recognize RPL-unaware leaf nodes because it will receive
a DAO about that node from the 6LR immediately above that RPL-unaware
node.
The Non-Storing mode case does not require the Type change from 0x63
to 0x23, as the root can always create the right packet. The Type
change does not adversely affect the Non-Storing case (see
Section 4.1.3).
4.3. Updates to RFC 8138: Indicating the Way to Decompress with the New
RPI Option Type
This modification is required in order to be able to decompress the
RPL Option with the new Option Type of 0x23.
The RPI-6LoRH header provides a compressed form for the RPL RPI; see
[RFC8138], Section 6. A node that is decompressing this header MUST
decompress using the RPI Option Type that is currently active, that
is, a choice between 0x23 (new) and 0x63 (old). The node will know
which to use based upon the presence of the flag in the DODAG
Configuration option defined in Section 4.1.3. For example, if the
network is in 0x23 mode (by DIO option), then it should be
decompressed to 0x23.
Section 7 of [RFC8138] documents how to compress the IPv6-in-IPv6
header.
There are potential significant advantages to having a single code
path that always processes IPv6-in-IPv6 headers with no conditional
branches.
In Storing mode, the scenarios where the flow goes from RAL to RUL
and RUL to RUL include compression of the IPv6-in-IPv6 and RPI
headers. The IPv6-in-IPv6 header MUST be used in this case, and it
SHOULD be compressed as specified in [RFC8138], Section 7. Figure 2
illustrates the case in Storing mode where the packet is received
from the Internet, then the root encapsulates the packet to insert
the RPI. In that example, the leaf is not known to support RFC 8138,
and the packet is encapsulated to the 6LR that is the parent and last
hop to the final destination.
+-+ ... -+-+ ... +-+- ... -+-+- +-+-+-+ ... +-+-+ ... -+++ ... +-...
|11110001|SRH-6LoRH| RPI- |IP-in-IP| NH=1 |11110CPP| UDP | UDP
|Page 1 |Type1 S=0| 6LoRH |6LoRH |LOWPAN_IPHC| UDP | hdr |Payld
+-+ ... -+-+ ... +-+- ... -+-+-.+-+-+-+-+ ... +-+-+ ... -+ ... +-...
<-4bytes-> <- RFC 6282 ->
No RPL artifact
Figure 2: RPI Inserted by the Root in Storing Mode
In Figure 2, the source of the IPv6-in-IPv6 encapsulation is the
root, so it is elided in the IP-in-IP 6LoRH. The destination is the
parent 6LR of the destination of the inner packet so it cannot be
elided. It is placed as the single entry in a Source Route Header
6LoRH (SRH-6LoRH) as the first 6LoRH. There is a single entry so the
SRH-6LoRH Size is zero. In that example, the Type is 1 so the 6LR
address is compressed to two bytes. This results in the total length
of the SRH-6LoRH being four bytes. The RPI-6LoRH and then the IP-in-
IP 6LoRH follow. When the IP-in-IP 6LoRH is removed, all the router
headers that precede it are also removed. The Paging Dispatch
[RFC8025] may also be removed if there was no previous Page change to
a Page other than 0 or 1, since the LOWPAN_IPHC is encoded in the
same fashion in the default Page 0 and in Page 1. The resulting
packet to the destination is the inner packet compressed with
[RFC6282].
5. Reference Topology
A RPL network in general is composed of a 6LBR, a Backbone Router
(6BBR), a 6LR, and a 6LN as a leaf logically organized in a DODAG
structure.
Figure 3 shows the reference RPL topology for this document. The
nodes are labeled with letters so that they may be referenced in
subsequent sections. In the figure, 6LR represents a full router
node. The 6LN is a RPL-aware router or host (as a leaf).
Additionally, for simplification purposes, it is supposed that the
6LBR has direct access to Internet and is the root of the DODAG, thus
the 6BBR is not present in the figure.
The 6LN leaves marked as RAL (F, H, and I) are RPL nodes with no
children hosts.
The leaves marked as RUL (G and J) are devices that do not speak RPL
at all (RPL unaware), but use Router Advertisements, 6LoWPAN
Duplicate Address Request and Duplicate Address Confirmation (DAR/
DAC), and 6LoWPAN Neighbor Discovery (ND) only to participate in the
network [RFC8505]. In the document, these leaves (G and J) are also
referred to as a RUL.
The 6LBR (A) in the figure is the root of the Global DODAG.
+------------+
| INTERNET ----------+
| | |
+------------+ |
|
|
|
A |
+-------+
|6LBR |
+-----------|(root) |-------+
| +-------+ |
| |
| |
| |
| |
| B |C
+---|---+ +---|---+
| 6LR | | 6LR |
+---------| |--+ +--- ---+
| +-------+ | | +-------+ |
| | | |
| | | |
| | | |
| | | |
| D | E | |
+-|-----+ +---|---+ | |
| 6LR | | 6LR | | |
| | +------ | | |
+---|---+ | +---|---+ | |
| | | | |
| | +--+ | |
| | | | |
| | | | |
| | | I | J |
F | | G | H | |
+-----+-+ +-|-----+ +---|--+ +---|---+ +---|---+
| RAL | | RUL | | RAL | | RAL | | RUL |
| 6LN | | 6LN | | 6LN | | 6LN | | 6LN |
+-------+ +-------+ +------+ +-------+ +-------+
Figure 3: A Reference RPL Topology
6. Use Cases
In the data plane, a combination of RFC 6553, RFC 6554, and IPv6-in-
IPv6 encapsulation are going to be analyzed for a number of
representative traffic flows.
The use cases describe the communication in the following cases:
* Between RPL-aware nodes with the root (6LBR)
* Between RPL-aware nodes with the Internet
* Between RUL nodes within the LLN (e.g., see Section 7.1.4)
* Inside of the LLN when the final destination address resides
outside of the LLN (e.g., see Section 7.2.3)
The use cases are as follows:
Interaction between leaf and root:
RAL to root
root to RAL
RUL to root
root to RUL
Interaction between leaf and Internet:
RAL to Internet
Internet to RAL
RUL to Internet
Internet to RUL
Interaction between leaves:
RAL to RAL
RAL to RUL
RUL to RAL
RUL to RUL
This document is consistent with the rule that a header cannot be
inserted or removed on the fly inside an IPv6 packet that is being
routed. This is a fundamental precept of the IPv6 architecture as
outlined in [RFC8200].
As the Rank information in the RPI artifact is changed at each hop,
it will typically be zero when it arrives at the DODAG root. The
DODAG root MUST force it to zero when passing the packet out to the
Internet. The Internet will therefore not see any SenderRank
information.
Despite being legal to leave the RPI artifact in place, an
intermediate router that needs to add an extension header (e.g., RH3
or RPL Option) MUST still encapsulate the packet in an (additional)
outer IP header. The new header is placed after this new outer IP
header.
A corollary is that an intermediate router can remove an RH3 or RPL
Option only if it is placed in an encapsulating IPv6 header that is
addressed _to_ this intermediate router. When doing the above, the
whole encapsulating header must be removed. (A replacement may be
added.)
Both the RPL Option and the RH3 headers may be modified in very
specific ways by routers on the path of the packet without the need
to add and remove an encapsulating header. Both headers were
designed with this modification in mind, and both the RPL RH3 and the
RPL Option are marked mutable but recoverable: so an IPsec
Authentication Header (AH) can be applied across these headers, but
it cannot secure the values that mutate.
The RPI MUST be present in every single RPL data packet.
Prior to [RFC8138], there was significant interest in creating an
exception to this rule and removing the RPI for Downward flows in
Non-Storing mode. This exception covered a very small number of
cases, and caused significant interoperability challenges while
adding significant interest in the code and tests. The ability to
compress the RPI down to three bytes or less removes much of the
pressure to optimize this any further.
Throughout the following subsections, the examples are described in
more detail in the first subsections, and more concisely in the later
ones.
The use cases are delineated based on the following IPV6 and RPL
mandates:
The RPI has to be in every packet that traverses the LLN.
- Because of the above requirement, packets from the Internet
have to be encapsulated.
- A header cannot be inserted or removed on the fly inside an
IPv6 packet that is being routed.
- Extension headers may not be added or removed except by the
sender or the receiver.
- RPI and RH3 headers may be modified by routers on the path of
the packet without the need to add and remove an encapsulating
header.
- An RH3 or RPL Option can only be removed by an intermediate
router if it is placed in an encapsulating IPv6 header, which
is addressed to the intermediate router.
- The Non-Storing mode requires downstream encapsulation by the
root for RH3.
The use cases are delineated based on the following assumptions:
This document assumes that the LLN is using the no-drop RPI Option
Type (0x23).
- Each IPv6 node (including Internet routers) obeys [RFC8200], so
that the 0x23 RPI Option Type can be safely inserted.
- All 6LRs obey [RFC8200].
- The RPI is ignored at the IPv6 destination (dst) node (RUL).
- In the use cases, we assume that the RAL supports IP-in-IP
encapsulation.
- In the use cases, we don't assume that the RUL supports IP-in-
IP encapsulation.
- For traffic leaving a RUL, if the RUL adds an opaque RPI, then
the 6LR as a RPL Border Router SHOULD rewrite the RPI to
indicate the selected Instance and set the flags.
- The description for RALs applies to RAN in general.
- Unconstrained uses of RPL are not in scope of this document.
- Compression is based on [RFC8138].
- The flow label [RFC6437] is not needed in RPL.
7. Storing Mode
In Storing mode (SM) (fully stateful), the sender can determine if
the destination is inside the LLN by looking if the destination
address is matched by the DIO's Prefix Information Option (PIO)
option.
Table 4 itemizes which headers are needed in each of the following
scenarios. It indicates whether an IPv6-in-IPv6 header must be added
and to which destination it must be addressed:
1. the final destination (the RAL node that is the target (tgt)),
2. the "root", or
3. the 6LR parent of a RUL.
In cases where no IPv6-in-IPv6 header is needed, the column states
"No", and the destination is N/A (Not Applicable). If the IPv6-in-
IPv6 header is needed, the column shows "must".
In all cases, the RPI is needed, since it identifies inconsistencies
(loops) in the routing topology. In general, the RH3 is not needed
because it is not used in Storing mode. However, there is one
scenario (from the root to the RUL in SM) where the RH3 can be used
to point at the RUL (Table 8).
The leaf can be a router 6LR or a host, both indicated as 6LN. The
root refers to the 6LBR (see Figure 3).
+=====================+==========+==============+==================+
| Interaction between | Use Case | IPv6-in-IPv6 | IPv6-in-IPv6 dst |
+=====================+==========+==============+==================+
| Leaf - Root | RAL to | No | N/A |
| | root | | |
| +----------+--------------+------------------+
| | root to | No | N/A |
| | RAL | | |
| +----------+--------------+------------------+
| | root to | must | 6LR |
| | RUL | | |
| +----------+--------------+------------------+
| | RUL to | must | root |
| | root | | |
+=====================+----------+--------------+------------------+
| Leaf - Internet | RAL to | may | root |
| | Int | | |
| +----------+--------------+------------------+
| | Int to | must | RAL (tgt) |
| | RAL | | |
| +----------+--------------+------------------+
| | RUL to | must | root |
| | Int | | |
| +----------+--------------+------------------+
| | Int to | must | 6LR |
| | RUL | | |
+=====================+----------+--------------+------------------+
| Leaf - Leaf | RAL to | No | N/A |
| | RAL | | |
| +----------+--------------+------------------+
| | RAL to | No(up) | N/A |
| | RUL +--------------+------------------+
| | | must(down) | 6LR |
| +----------+--------------+------------------+
| | RUL to | must(up) | root |
| | RAL +--------------+------------------+
| | | must(down) | RAL |
| +----------+--------------+------------------+
| | RUL to | must(up) | root |
| | RUL +--------------+------------------+
| | | must(down) | 6LR |
+=====================+----------+--------------+------------------+
Table 4: IPv6-in-IPv6 Encapsulation in Storing Mode
7.1. Storing Mode: Interaction between Leaf and Root
This section describes the communication flow in Storing mode (SM)
between the following:
RAL to root
root to RAL
RUL to root
root to RUL
7.1.1. SM: Example of Flow from RAL to Root
In Storing mode, RPI [RFC6553] is used to send the RPLInstanceID and
Rank information.
In this case, the flow comprises:
RAL (6LN) --> 6LR_i --> root (6LBR)
For example, a communication flow could be: Node F (6LN) --> Node D
(6LR_i) --> Node B (6LR_i) --> Node A root (6LBR)
The RAL (Node F) inserts the RPI, and sends the packet to the 6LR
(Node D), which decrements the Rank in the RPI and sends the packet
up. When the packet arrives at the 6LBR (Node A), the RPI is removed
and the packet is processed.
No IPv6-in-IPv6 header is required.
The RPI can be removed by the 6LBR because the packet is addressed to
the 6LBR. The RAL must know that it is communicating with the 6LBR
to make use of this scenario. The RAL can know the address of the
6LBR because it knows the address of the root via the DODAGID in the
DIO messages.
Table 5 summarizes which headers are needed for this use case.
+===================+=========+=======+==========+
| Header | RAL src | 6LR_i | 6LBR dst |
+===================+=========+=======+==========+
| Added headers | RPI | -- | -- |
+===================+---------+-------+----------+
| Modified headers | -- | RPI | -- |
+===================+---------+-------+----------+
| Removed headers | -- | -- | RPI |
+===================+---------+-------+----------+
| Untouched headers | -- | -- | -- |
+===================+---------+-------+----------+
Table 5: SM: Summary of the Use of Headers
from RAL to Root
7.1.2. SM: Example of Flow from Root to RAL
In this case, the flow comprises:
root (6LBR) --> 6LR_i --> RAL (6LN)
For example, a communication flow could be: Node A root (6LBR) -->
Node B (6LR_i) --> Node D (6LR_i) --> Node F (6LN)
In this case, the 6LBR inserts RPI and sends the packet down. The
6LR increments the Rank in the RPI (it examines the RPLInstanceID to
identify the right forwarding table). The packet is processed in the
RAL, and the RPI is removed.
No IPv6-in-IPv6 header is required.
Table 6 summarizes which headers are needed for this use case.
+===================+==========+=======+=========+
| Header | 6LBR src | 6LR_i | RAL dst |
+===================+==========+=======+=========+
| Added headers | RPI | -- | -- |
+===================+----------+-------+---------+
| Modified headers | -- | RPI | -- |
+===================+----------+-------+---------+
| Removed headers | -- | -- | RPI |
+===================+----------+-------+---------+
| Untouched headers | -- | -- | -- |
+===================+----------+-------+---------+
Table 6: SM: Summary of the Use of Headers
from Root to RAL
7.1.3. SM: Example of Flow from Root to RUL
In this case, the flow comprises:
root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)
For example, a communication flow could be: Node A (6LBR) --> Node B
(6LR_i) --> Node E (6LR_n) --> Node G (RUL)
6LR_i (Node B) represents the intermediate routers from the source
(6LBR) to the destination (RUL), and 1 <= i <= n, where n is the
total number of routers (6LR) that the packet goes through, from the
6LBR (Node A) to the RUL (Node G).
The 6LBR will encapsulate the packet in an IPv6-in-IPv6 header and
prepend an RPI. The IPv6-in-IPv6 header is addressed to the 6LR
parent of the RUL (6LR_n). The 6LR parent of the RUL removes the
header and sends the packet to the RUL.
Table 7 summarizes which headers are needed for this use case.
+==================+===============+=========+=========+=========+
| Header | 6LBR src | 6LR_i | 6LR_n | RUL dst |
+==================+===============+=========+=========+=========+
| Added headers | IP6-IP6 (RPI) | -- | -- | -- |
+==================+---------------+---------+---------+---------+
| Modified headers | -- | RPI | -- | -- |
+==================+---------------+---------+---------+---------+
| Removed headers | -- | -- | IP6-IP6 | -- |
| | | | (RPI) | |
+==================+---------------+---------+---------+---------+
| Untouched | -- | IP6-IP6 | -- | -- |
| headers | | | | |
+==================+---------------+---------+---------+---------+
Table 7: SM: Summary of the Use of Headers from Root to RUL
IP-in-IP encapsulation may be avoided for root-to-RUL communication.
In SM, it can be replaced by a loose RH3 header that indicates the
RUL. In which case, the packet is routed to the 6LR as a normal SM
operation, then the 6LR forwards to the RUL based on the RH3, and the
RUL ignores both the consumed RH3 and the RPI, as in Non-Storing
mode.
Table 8 summarizes which headers are needed for this scenario.
+===========+======+==============+===============+================+
| Header | 6LBR | 6LR_i | 6LR_n | RUL dst |
| | src | i=(1,..,n-1) | | |
+===========+======+==============+===============+================+
| Added | RPI, | -- | -- | -- |
| headers | RH3 | | | |
+===========+------+--------------+---------------+----------------+
| Modified | -- | RPI | RPI, | -- |
| headers | | | RH3(consumed) | |
+===========+------+--------------+---------------+----------------+
| Removed | -- | -- | -- | -- |
| headers | | | | |
+===========+------+--------------+---------------+----------------+
| Untouched | -- | RH3 | -- | RPI, RH3 (both |
| headers | | | | ignored) |
+===========+------+--------------+---------------+----------------+
Table 8: SM: Summary of the Use of Headers from Root to RUL without
Encapsulation
7.1.4. SM: Example of Flow from RUL to Root
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_i --> root (6LBR)
For example, a communication flow could be: Node G (RUL) --> Node E
(6LR_1) --> Node B (6LR_i) --> Node A root (6LBR)
6LR_i represents the intermediate routers from the source (RUL) to
the destination (6LBR), and 1 <= i <= n, where n is the total number
of routers (6LR) that the packet goes through, from the RUL to the
6LBR.
When the packet arrives from the RUL (Node G) to 6LR_1 (Node E), the
6LR_1 will encapsulate the packet in an IPv6-in-IPv6 header with an
RPI. The IPv6-in-IPv6 header is addressed to the root (Node A). The
root removes the header and processes the packet.
Table 9 summarizes which headers are needed for this use case where
the IPv6-in-IPv6 header is addressed to the root (Node A).
+==================+=========+===============+=========+==========+
| Header | RUL src | 6LR_1 | 6LR_i | 6LBR dst |
+==================+=========+===============+=========+==========+
| Added headers | -- | IP6-IP6 (RPI) | -- | -- |
+==================+---------+---------------+---------+----------+
| Modified headers | -- | -- | RPI | -- |
+==================+---------+---------------+---------+----------+
| Removed headers | -- | -- | -- | IP6-IP6 |
| | | | | (RPI) |
+==================+---------+---------------+---------+----------+
| Untouched | -- | -- | IP6-IP6 | -- |
| headers | | | | |
+==================+---------+---------------+---------+----------+
Table 9: SM: Summary of the Use of Headers from RUL to Root
7.2. SM: Interaction between Leaf and Internet
This section describes the communication flow in Storing mode (SM)
between the following:
RAL to Internet
Internet to RAL
RUL to Internet
Internet to RUL
7.2.1. SM: Example of Flow from RAL to Internet
In this case, the flow comprises:
RAL (6LN) --> 6LR_i --> root (6LBR) --> Internet
For example, the communication flow could be: Node F (RAL) --> Node D
(6LR_i) --> Node B (6LR_i) --> Node A root (6LBR) --> Internet
6LR_i represents the intermediate routers from the source (RAL) to
the root (6LBR), and 1 <= i <= n, where n is the total number of
routers (6LR) that the packet goes through, from the RAL to the 6LBR.
RPL information from RFC 6553 may go out to Internet as it will be
ignored by nodes that have not been configured to be RPL aware. No
IPv6-in-IPv6 header is required.
On the other hand, the RAL may insert the RPI encapsulated in an
IPv6-in-IPv6 header to the root. Thus, the root removes the RPI and
sends the packet to the Internet.
| Note: In this use case, a leaf node is used, but this use case
| can also be applicable to any RPL-aware node type (e.g., 6LR).
Table 10 summarizes which headers are needed for this use case when
there is no encapsulation. Note that the RPI is modified by 6LBR to
set the SenderRank to zero in the case that it is not already zero.
Table 11 summarizes which headers are needed when encapsulation to
the root takes place.
+===================+=========+=======+======+===============+
| Header | RAL src | 6LR_i | 6LBR | Internet dst |
+===================+=========+=======+======+===============+
| Added headers | RPI | -- | -- | -- |
+===================+---------+-------+------+---------------+
| Modified headers | -- | RPI | RPI | -- |
+===================+---------+-------+------+---------------+
| Removed headers | -- | -- | -- | -- |
+===================+---------+-------+------+---------------+
| Untouched headers | -- | -- | -- | RPI (Ignored) |
+===================+---------+-------+------+---------------+
Table 10: SM: Summary of the Use of Headers from RAL to
Internet with No Encapsulation
+===============+===============+=========+=========+==============+
| Header | RAL src | 6LR_i | 6LBR | Internet dst |
+===============+===============+=========+=========+==============+
| Added headers | IP6-IP6 (RPI) | -- | -- | -- |
+===============+---------------+---------+---------+--------------+
| Modified | -- | RPI | -- | -- |
| headers | | | | |
+===============+---------------+---------+---------+--------------+
| Removed | -- | -- | IP6-IP6 | -- |
| headers | | | (RPI) | |
+===============+---------------+---------+---------+--------------+
| Untouched | -- | IP6-IP6 | -- | -- |
| headers | | | | |
+===============+---------------+---------+---------+--------------+
Table 11: SM: Summary of the Use of Headers from RAL to Internet
with Encapsulation to the Root (6LBR)
7.2.2. SM: Example of Flow from Internet to RAL
In this case, the flow comprises:
Internet --> root (6LBR) --> 6LR_i --> RAL (6LN)
For example, a communication flow could be: Internet --> Node A root
(6LBR) --> Node B (6LR_1) --> Node D (6LR_n) --> Node F (RAL)
When the packet arrives from Internet to 6LBR, the RPI is added in a
outer IPv6-in-IPv6 header (with the IPv6-in-IPv6 destination address
set to the RAL) and sent to the 6LR, which modifies the Rank in the
RPI. When the packet arrives at the RAL, the packet is decapsulated,
which removes the RPI before the packet is processed.
Table 12 summarizes which headers are needed for this use case.
+==================+==============+===============+=======+=========+
| Header | Internet src | 6LBR | 6LR_i | RAL dst |
+==================+==============+===============+=======+=========+
| Added headers | -- | IP6-IP6 (RPI) | -- | -- |
+==================+--------------+---------------+-------+---------+
| Modified | -- | -- | RPI | -- |
| headers | | | | |
+==================+--------------+---------------+-------+---------+
| Removed | -- | -- | -- | IP6-IP6 |
| headers | | | | (RPI) |
+==================+--------------+---------------+-------+---------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+==================+--------------+---------------+-------+---------+
Table 12: SM: Summary of the Use of Headers from Internet to RAL
7.2.3. SM: Example of Flow from RUL to Internet
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_i --> root (6LBR) --> Internet
For example, a communication flow could be: Node G (RUL) --> Node E
(6LR_1) --> Node B (6lR_i) --> Node A root (6LBR) --> Internet
The node 6LR_1 (i=1) will add an IPv6-in-IPv6 (RPI) header addressed
to the root such that the root can remove the RPI before passing
upwards. In the intermediate 6LR, the Rank in the RPI is modified.
The originating node will ideally leave the IPv6 flow label as zero
so that the packet can be better compressed through the LLN. The
6LBR will set the flow label of the packet to a non-zero value when
sending to the Internet. For details, check [RFC6437].
Table 13 summarizes which headers are needed for this use case.
+===========+==========+=========+============+=========+==========+
| Header | IPv6 src | 6LR_1 | 6LR_i | 6LBR | Internet |
| | (RUL) | | i=(2,..,n) | | dst |
+===========+==========+=========+============+=========+==========+
| Added | -- | IP6-IP6 | -- | -- | -- |
| headers | | (RPI) | | | |
+===========+----------+---------+------------+---------+----------+
| Modified | -- | -- | RPI | -- | -- |
| headers | | | | | |
+===========+----------+---------+------------+---------+----------+
| Removed | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | (RPI) | |
+===========+----------+---------+------------+---------+----------+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+===========+----------+---------+------------+---------+----------+
Table 13: SM: Summary of the Use of Headers from RUL to Internet
7.2.4. SM: Example of Flow from Internet to RUL
In this case, the flow comprises:
Internet --> root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)
For example, a communication flow could be: Internet --> Node A root
(6LBR) --> Node B (6LR_i) --> Node E (6LR_n) --> Node G (RUL)
The 6LBR will have to add an RPI within an IPv6-in-IPv6 header. The
IPv6-in-IPv6 encapsulating header is addressed to the 6LR parent of
the RUL.
Further details about this are mentioned in [RFC9010], which
specifies RPL routing for a 6LN acting as a plain host and being
unaware of RPL.
The 6LBR may set the flow label on the inner IPv6-in-IPv6 header to
zero in order to aid in compression [RFC8138] [RFC6437].
Table 14 summarizes which headers are needed for this use case.
+===========+==============+=========+==============+=========+=====+
| Header | Internet | 6LBR | 6LR_i | 6LR_n | RUL |
| | src | | i=(1,..,n-1) | | dst |
+===========+==============+=========+==============+=========+=====+
| Added | -- | IP6-IP6 | -- | -- | -- |
| headers | | (RPI) | | | |
+===========+--------------+---------+--------------+---------+-----+
| Modified | -- | -- | RPI | -- | -- |
| headers | | | | | |
+===========+--------------+---------+--------------+---------+-----+
| Removed | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | (RPI) | |
+===========+--------------+---------+--------------+---------+-----+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+===========+--------------+---------+--------------+---------+-----+
Table 14: SM: Summary of the Use of Headers from Internet to RUL
7.3. SM: Interaction between Leaf and Leaf
This section describes the communication flow in Storing mode (SM)
between the following:
RAL to RAL
RAL to RUL
RUL to RAL
RUL to RUL
7.3.1. SM: Example of Flow from RAL to RAL
In [RFC6550], RPL allows a simple, one-hop optimization for both
Storing and Non-Storing networks. A node may send a packet destined
to a one-hop neighbor directly to that node. See Section 9 of
[RFC6550].
When the nodes are not directly connected, then the flow comprises
the following in the Storing mode:
RAL src (6LN) --> 6LR_ia --> common parent (6LR_x) --> 6LR_id --> RAL
dst (6LN)
For example, a communication flow could be: Node F (RAL src) --> Node
D (6LR_ia) --> Node B (6LR_x) --> Node E (6LR_id) --> Node H (RAL
dst)
6LR_ia (Node D) represents the intermediate routers from the source
to the common parent 6LR_x (Node B), and 1 <= ia <= n, where n is the
total number of routers (6LR) that the packet goes through, from the
RAL (Node F) to the common parent 6LR_x (Node B).
6LR_id (Node E) represents the intermediate routers from the common
parent 6LR_x (Node B) to the destination RAL (Node H), and 1 <= id <=
m, where m is the total number of routers (6LR) that the packet goes
through, from the common parent (6LR_x) to the destination RAL (Node
H).
It is assumed that the two nodes are in the same RPL domain (that
they share the same DODAG root). At the common parent (Node B), the
direction flag ('O' flag) of the RPI is changed (from decreasing
ranks to increasing ranks).
While the 6LR nodes will update the RPI, no node needs to add or
remove the RPI, so no IPv6-in-IPv6 headers are necessary.
Table 15 summarizes which headers are needed for this use case.
+===========+=========+========+===============+========+=====+
| Header | RAL src | 6LR_ia | 6LR_x (common | 6LR_id | RAL |
| | | | parent) | | dst |
+===========+=========+========+===============+========+=====+
| Added | RPI | -- | -- | -- | -- |
| headers | | | | | |
+===========+---------+--------+---------------+--------+-----+
| Modified | -- | RPI | RPI | RPI | -- |
| headers | | | | | |
+===========+---------+--------+---------------+--------+-----+
| Removed | -- | -- | -- | -- | RPI |
| headers | | | | | |
+===========+---------+--------+---------------+--------+-----+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+===========+---------+--------+---------------+--------+-----+
Table 15: SM: Summary of the Use of Headers from RAL to RAL
7.3.2. SM: Example of Flow from RAL to RUL
In this case, the flow comprises:
RAL src (6LN) --> 6LR_ia --> common parent (6LBR, the root) -->
6LR_id --> RUL (IPv6 dst node)
For example, a communication flow could be: Node F (RAL) --> Node D
--> Node B --> Node A --> Node B --> Node E --> Node G (RUL)
6LR_ia represents the intermediate routers from the source (RAL) to
the common parent (the root), and 1 <= ia <= n, where n is the total
number of routers (6LR) that the packet goes through, from the RAL to
the root.
6LR_id (Node E) represents the intermediate routers from the root
(Node B) to the destination RUL (Node G). In this case, 1 <= id <=
m, where m is the total number of routers (6LR) that the packet goes
through, from the root down to the destination RUL.
In this case, the packet from the RAL goes to the 6LBR because the
route to the RUL is not injected into the RPL SM. Thus, the RAL
inserts an RPI (RPI1) addressed to the root (6LBR). The root does
not remove the RPI1 (the root cannot remove an RPI if there is no
encapsulation). The root inserts an IPv6-in-IPv6 encapsulation with
an RPI2 and sends it to the 6LR parent of the RUL, which removes the
encapsulation and RPI2 before passing the packet to the RUL.
Table 16 summarizes which headers are needed for this use case.
+===========+=====+========+=========+========+=========+===========+
| Header | RAL | 6LR_ia | 6LBR | 6LR_id | 6LR_m | RUL dst |
| | src | | | | | |
+===========+=====+========+=========+========+=========+===========+
| Added | RPI1| -- | IP6-IP6 | -- | -- | -- |
| headers | | | (RPI2) | | | |
+===========+-----+--------+---------+--------+---------+-----------+
| Modified | -- | RPI1 | -- | RPI2 | -- | -- |
| headers | | | | | | |
+===========+-----+--------+---------+--------+---------+-----------+
| Removed | -- | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | | (RPI2) | |
+===========+-----+--------+---------+--------+---------+-----------+
| Untouched | -- | -- | RPI1 | RPI1 | RPI1 | RPI1 |
| headers | | | | | | (ignored) |
+===========+-----+--------+---------+--------+---------+-----------+
Table 16: SM: Summary of the Use of Headers from RAL to RUL
7.3.3. SM: Example of Flow from RUL to RAL
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_ia --> 6LBR --> 6LR_id --> RAL dst (6LN)
For example, a communication flow could be: Node G (RUL) --> Node E
--> Node B --> Node A --> Node B --> Node D --> Node F (RAL)
6LR_ia (Node E) represents the intermediate routers from the source
(RUL) (Node G) to the root (Node A). In this case, 1 <= ia <= n,
where n is the total number of routers (6LR) that the packet goes
through, from the source to the root.
6LR_id represents the intermediate routers from the root (Node A) to
the destination RAL (Node F). In this case, 1 <= id <= m, where m is
the total number of routers (6LR) that the packet goes through, from
the root to the destination RAL.
The 6LR_1 (Node E) receives the packet from the RUL (Node G) and
inserts the RPI (RPI1) encapsulated in an IPv6-in-IPv6 header to the
root. The root removes the outer header including the RPI (RPI1) and
inserts a new RPI (RPI2) addressed to the destination RAL (Node F).
Table 17 summarizes which headers are needed for this use case.
+===========+=====+=========+========+=========+========+=========+
| Header | RUL | 6LR_1 | 6LR_ia | 6LBR | 6LR_id | RAL dst |
| | src | | | | | |
+===========+=====+=========+========+=========+========+=========+
| Added | -- | IP6-IP6 | -- | IP6-IP6 | -- | -- |
| headers | | (RPI1) | | (RPI2) | | |
+===========+-----+---------+--------+---------+--------+---------+
| Modified | -- | -- | RPI1 | -- | RPI2 | -- |
| headers | | | | | | |
+===========+-----+---------+--------+---------+--------+---------+
| Removed | -- | -- | -- | IP6-IP6 | -- | IP6-IP6 |
| headers | | | | (RPI1) | | (RPI2) |
+===========+-----+---------+--------+---------+--------+---------+
| Untouched | -- | -- | -- | -- | -- | -- |
| headers | | | | | | |
+===========+-----+---------+--------+---------+--------+---------+
Table 17: SM: Summary of the Use of Headers from RUL to RAL
7.3.4. SM: Example of Flow from RUL to RUL
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_ia --> 6LBR --> 6LR_id --> RUL
(IPv6 dst node)
For example, a communication flow could be: Node G (RUL src) --> Node
E --> Node B --> Node A (root) --> Node C --> Node J (RUL dst)
Internal nodes 6LR_ia (e.g., Node E or Node B) is the intermediate
router from the RUL source (Node G) to the root (6LBR) (Node A). In
this case, 1 <= ia <= n, where n is the total number of routers (6LR)
that the packet goes through, from the RUL to the root. 6LR_1 applies
when ia=1.
6LR_id (Node C) represents the intermediate routers from the root
(Node A) to the destination RUL (Node J). In this case, 1 <= id <=
m, where m is the total number of routers (6LR) that the packet goes
through, from the root to the destination RUL.
The 6LR_1 (Node E) receives the packet from the RUL (Node G) and adds
the RPI (RPI1) in an IPv6-in-IPv6 encapsulation directed to the root.
The root removes the outer header including the RPI (RPI1) and
inserts a new RPI (RPI2) addressed to the 6LR parent of the RUL.
Table 18 summarizes which headers are needed for this use case.
+===========+===+=========+========+=========+========+=========+===+
| Header |RUL| 6LR_1 | 6LR_ia | 6LBR | 6LR_id | 6LR_n |RUL|
| |src| | | | | |dst|
+===========+===+=========+========+=========+========+=========+===+
| Added | --| IP6-IP6 | -- | IP6-IP6 | -- | -- | --|
| headers | | (RPI1) | | (RPI1) | | | |
+===========+---+---------+--------+---------+--------+---------+---+
| Modified | --| -- | RPI1 | -- | RPI2 | -- | --|
| headers | | | | | | | |
+===========+---+---------+--------+---------+--------+---------+---+
| Removed | --| -- | -- | IP6-IP6 | -- | IP6-IP6 | --|
| headers | | | | (RPI1) | | (RPI2) | |
+===========+---+---------+--------+---------+--------+---------+---+
| Untouched | --| -- | -- | -- | -- | -- | --|
| headers | | | | | | | |
+===========+---+---------+--------+---------+--------+---------+---+
Table 18: SM: Summary of the Use of Headers from RUL to RUL
8. Non-Storing Mode
In Non-Storing mode (Non-SM) (fully source routed), the 6LBR (DODAG
root) has complete knowledge about the connectivity of all DODAG
nodes and all traffic flows through the root node. Thus, there is no
need for all nodes to know about the existence of RPL-unaware nodes.
Only the 6LBR needs to act if compensation is necessary for RPL-
unaware receivers.
Table 19 summarizes which headers are needed in the following
scenarios and indicates when the RPI, RH3, and IPv6-in-IPv6 header
are to be inserted. The last column depicts the target destination
of the IPv6-in-IPv6 header: 6LN (indicated by "RAL"), 6LR (parent of
a RUL), or the root. In cases where no IPv6-in-IPv6 header is
needed, the column indicates "No". There is no expectation on RPL
that RPI can be omitted because it is needed for routing, quality of
service, and compression. This specification expects that an RPI is
always present. The term "may(up)" means that the IPv6-in-IPv6
header may be necessary in the Upward direction. The term "must(up)"
means that the IPv6-in-IPv6 header must be present in the Upward
direction. The term "must(down)" means that the IPv6-in-IPv6 header
must be present in the Downward direction.
The leaf can be a router 6LR or a host, both indicated as 6LN
(Figure 3). In Table 19, the (1) indicates a 6TiSCH case [RFC8180],
where the RPI may still be needed for the RPLInstanceID to be
available for priority/channel selection at each hop.
+=============+========+=====+=====+==============+==========+
| Interaction | Use | RPI | RH3 | IPv6-in-IPv6 | IP-in-IP |
| between | Case | | | | dst |
+=============+========+=====+=====+==============+==========+
| Leaf - Root | RAL to | Yes | No | No | No |
| | root | | | | |
| +--------+-----+-----+--------------+----------+
| | root | Yes | Yes | No | No |
| | to RAL | | | | |
| +--------+-----+-----+--------------+----------+
| | root | Yes | Yes | No | 6LR |
| | to RUL | (1) | | | |
| +--------+-----+-----+--------------+----------+
| | RUL to | Yes | No | must | root |
| | root | | | | |
+=============+--------+-----+-----+--------------+----------+
| Leaf - | RAL to | Yes | No | may(up) | root |
| Internet | Int | | | | |
| +--------+-----+-----+--------------+----------+
| | Int to | Yes | Yes | must | RAL |
| | RAL | | | | |
| +--------+-----+-----+--------------+----------+
| | RUL to | Yes | No | must | root |
| | Int | | | | |
| +--------+-----+-----+--------------+----------+
| | Int to | Yes | Yes | must | 6LR |
| | RUL | | | | |
+=============+--------+-----+-----+--------------+----------+
| Leaf - Leaf | RAL to | Yes | Yes | may(up) | root |
| | RAL | | +--------------+----------+
| | | | | must(down) | RAL |
| +--------+-----+-----+--------------+----------+
| | RAL to | Yes | Yes | may(up) | root |
| | RUL | | +--------------+----------+
| | | | | must(down) | 6LR |
| +--------+-----+-----+--------------+----------+
| | RUL to | Yes | Yes | must(up) | root |
| | RAL | | +--------------+----------+
| | | | | must(down) | RAL |
| +--------+-----+-----+--------------+----------+
| | RUL to | Yes | Yes | must(up) | root |
| | RUL | | +--------------+----------+
| | | | | must(down) | 6LR |
+=============+--------+-----+-----+--------------+----------+
Table 19: Headers Needed in Non-Storing Mode: RPI, RH3,
IPv6-in-IPv6 Encapsulation
8.1. Non-Storing Mode: Interaction between Leaf and Root
This section describes the communication flow in Non-Storing mode
(Non-SM) between the following:
RAL to root
root to RAL
RUL to root
root to RUL
8.1.1. Non-SM: Example of Flow from RAL to Root
In Non-Storing mode, the leaf node uses default routing to send
traffic to the root. The RPI must be included since it contains the
Rank information, which is used to avoid and/or detect loops.
RAL (6LN) --> 6LR_i --> root(6LBR)
For example, a communication flow could be: Node F --> Node D -->
Node B --> Node A (root)
6LR_i represents the intermediate routers from the source to the
destination. In this case, 1 <= i <= n, where n is the total number
of routers (6LR) that the packet goes through, from the source (RAL)
to the destination (6LBR).
This situation is the same case as Storing mode.
Table 20 summarizes which headers are needed for this use case.
+===================+=========+=======+==========+
| Header | RAL src | 6LR_i | 6LBR dst |
+===================+=========+=======+==========+
| Added headers | RPI | -- | -- |
+===================+---------+-------+----------+
| Modified headers | -- | RPI | -- |
+===================+---------+-------+----------+
| Removed headers | -- | -- | RPI |
+===================+---------+-------+----------+
| Untouched headers | -- | -- | -- |
+===================+---------+-------+----------+
Table 20: Non-SM: Summary of the Use of
Headers from RAL to Root
8.1.2. Non-SM: Example of Flow from Root to RAL
In this case, the flow comprises:
root (6LBR) --> 6LR_i --> RAL (6LN)
For example, a communication flow could be: Node A (root) --> Node B
--> Node D --> Node F
6LR_i represents the intermediate routers from the source to the
destination. In this case, 1 <= i <= n, where n is the total number
of routers (6LR) that the packet goes through, from the source (6LBR)
to the destination (RAL).
The 6LBR inserts an RH3 and an RPI. No IPv6-in-IPv6 header is
necessary as the traffic originates with a RPL-aware node, the 6LBR.
The destination is known to be RPL aware because the root knows the
whole topology in Non-Storing mode.
Table 21 summarizes which headers are needed for this use case.
+===================+==========+==========+==========+
| Header | 6LBR src | 6LR_i | RAL dst |
+===================+==========+==========+==========+
| Added headers | RPI, RH3 | -- | -- |
+===================+----------+----------+----------+
| Modified headers | -- | RPI, RH3 | -- |
+===================+----------+----------+----------+
| Removed headers | -- | -- | RPI, RH3 |
+===================+----------+----------+----------+
| Untouched headers | -- | -- | -- |
+===================+----------+----------+----------+
Table 21: Non-SM: Summary of the Use of Headers
from Root to RAL
8.1.3. Non-SM: Example of Flow from Root to RUL
In this case, the flow comprises:
root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)
For example, a communication flow could be: Node A (root) --> Node B
--> Node E --> Node G (RUL)
6LR_i represents the intermediate routers from the source to the
destination. In this case, 1 <= i <= n, where n is the total number
of routers (6LR) that the packet goes through, from the source (6LBR)
to the destination (RUL).
In the 6LBR, the RH3 is added; it is then modified at each
intermediate 6LR (6LR_1 and so on), and it is fully consumed in the
last 6LR (6LR_n) but is left in place. When the RPI is added, the
RUL, which does not understand the RPI, will ignore it (per
[RFC8200]); thus, encapsulation is not necessary.
Table 22 summarizes which headers are needed for this use case.
+===========+======+==============+===============+================+
| Header | 6LBR | 6LR_i | 6LR_n | RUL dst |
| | src | i=(1,..,n-1) | | |
+===========+======+==============+===============+================+
| Added | RPI, | -- | -- | -- |
| headers | RH3 | | | |
+===========+------+--------------+---------------+----------------+
| Modified | -- | RPI, RH3 | RPI, | -- |
| headers | | | RH3(consumed) | |
+===========+------+--------------+---------------+----------------+
| Removed | -- | -- | -- | -- |
| headers | | | | |
+===========+------+--------------+---------------+----------------+
| Untouched | -- | -- | -- | RPI, RH3 (both |
| headers | | | | ignored) |
+===========+------+--------------+---------------+----------------+
Table 22: Non-SM: Summary of the Use of Headers from Root to RUL
8.1.4. Non-SM: Example of Flow from RUL to Root
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_i --> root (6LBR) dst
For example, a communication flow could be: Node G --> Node E -->
Node B --> Node A (root)
6LR_i represents the intermediate routers from the source to the
destination. In this case, 1 <= i <= n, where n is the total number
of routers (6LR) that the packet goes through, from the source (RUL)
to the destination (6LBR). For example, 6LR_1 (i=1) is the router
that receives the packets from the RUL.
In this case, the RPI is added by the first 6LR (6LR_1) (Node E),
encapsulated in an IPv6-in-IPv6 header, and modified in the
subsequent 6LRs in the flow. The RPI and the entire packet are
consumed by the root.
Table 23 summarizes which headers are needed for this use case.
+===============+=========+==============+=======+==============+
| Header | RUL src | 6LR_1 | 6LR_i | 6LBR dst |
+===============+=========+==============+=======+==============+
| Added headers | -- | IPv6-in-IPv6 | -- | -- |
| | | (RPI) | | |
+===============+---------+--------------+-------+--------------+
| Modified | -- | -- | RPI | -- |
| headers | | | | |
+===============+---------+--------------+-------+--------------+
| Removed | -- | -- | -- | IPv6-in-IPv6 |
| headers | | | | (RPI) |
+===============+---------+--------------+-------+--------------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+===============+---------+--------------+-------+--------------+
Table 23: Non-SM: Summary of the Use of Headers from RUL to Root
8.2. Non-Storing Mode: Interaction between Leaf and Internet
This section describes the communication flow in Non-Storing mode
(Non-SM) between the following:
RAL to Internet
Internet to RAL
RUL to Internet
Internet to RUL
8.2.1. Non-SM: Example of Flow from RAL to Internet
In this case, the flow comprises:
RAL (6LN) src --> 6LR_i --> root (6LBR) --> Internet dst
For example, a communication flow could be: Node F (RAL) --> Node D
--> Node B --> Node A --> Internet. Having the RAL information about
the RPL domain, the packet may be encapsulated to the root when the
destination is not in the RPL domain of the RAL.
6LR_i represents the intermediate routers from the source to the
destination, and 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through, from the source (RAL) to the
6LBR.
In this case, the encapsulation from the RAL to the root is optional.
The simplest case is when the RPI gets to the Internet (as the
Table 24 shows it), knowing that the Internet is going to ignore it.
The IPv6 flow label should be set to zero to aid in compression
[RFC8138], and the 6LBR will set it to a non-zero value when sending
towards the Internet [RFC6437].
Table 24 summarizes which headers are needed for this use case when
no encapsulation is used. Table 25 summarizes which headers are
needed for this use case when encapsulation to the root is used.
+===================+=========+=======+======+===============+
| Header | RAL src | 6LR_i | 6LBR | Internet dst |
+===================+=========+=======+======+===============+
| Added headers | RPI | -- | -- | -- |
+===================+---------+-------+------+---------------+
| Modified headers | -- | RPI | RPI | -- |
+===================+---------+-------+------+---------------+
| Removed headers | -- | -- | -- | -- |
+===================+---------+-------+------+---------------+
| Untouched headers | -- | -- | -- | RPI (Ignored) |
+===================+---------+-------+------+---------------+
Table 24: Non-SM: Summary of the Use of Headers from RAL
to Internet with No Encapsulation
+===========+===============+=======+==============+==============+
| Header | RAL src | 6LR_i | 6LBR | Internet dst |
+===========+===============+=======+==============+==============+
| Added | IP6v6-in-IPv6 | -- | -- | -- |
| headers | (RPI) | | | |
+===========+---------------+-------+--------------+--------------+
| Modified | -- | RPI | -- | -- |
| headers | | | | |
+===========+---------------+-------+--------------+--------------+
| Removed | -- | -- | IPv6-in-IPv6 | -- |
| headers | | | (RPI) | |
+===========+---------------+-------+--------------+--------------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+===========+---------------+-------+--------------+--------------+
Table 25: Non-SM: Summary of the Use of Headers from RAL to
Internet with Encapsulation to the Root
8.2.2. Non-SM: Example of Flow from Internet to RAL
In this case, the flow comprises:
Internet --> root (6LBR) --> 6LR_i --> RAL dst (6LN)
For example, a communication flow could be: Internet --> Node A
(root) --> Node B --> Node D --> Node F (RAL)
6LR_i represents the intermediate routers from source to destination,
and 1 <= i <= n, where n is the total number of routers (6LR) that
the packet goes through, from the 6LBR to the destination (RAL).
The 6LBR must add an RH3 header. As the 6LBR will know the path and
address of the target node, it can address the IPv6-in-IPv6 header to
that node. The 6LBR will zero the flow label upon entry in order to
aid compression [RFC8138].
Table 26 summarizes which headers are needed for this use case.
+===========+==========+==============+==============+==============+
| Header | Internet | 6LBR | 6LR_i | RAL dst |
| | src | | | |
+===========+==========+==============+==============+==============+
| Added | -- | IPv6-in-IPv6 | -- | -- |
| headers | | (RH3, RPI) | | |
+===========+----------+--------------+--------------+--------------+
| Modified | -- | -- | IPv6-in-IPv6 | -- |
| headers | | | (RH3, RPI) | |
+===========+----------+--------------+--------------+--------------+
| Removed | -- | -- | -- | IPv6-in-IPv6 |
| headers | | | | (RH3, RPI) |
+===========+----------+--------------+--------------+--------------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+===========+----------+--------------+--------------+--------------+
Table 26: Non-SM: Summary of the Use of Headers from Internet to RAL
8.2.3. Non-SM: Example of Flow from RUL to Internet
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_i --> root (6LBR) --> Internet
dst
For example, a communication flow could be: Node G --> Node E -->
Node B --> Node A --> Internet
6LR_i represents the intermediate routers from the source to the
destination, and 1 <= i <= n, where n is the total number of routers
(6LRs) that the packet goes through, from the source (RUL) to the
6LBR, e.g., 6LR_1 (i=1).
In this case, the flow label is recommended to be zero in the RUL.
As the RUL parent adds RPL headers in the RUL packet, the first 6LR
(6LR_1) will add an RPI inside a new IPv6-in-IPv6 header. The IPv6-
in-IPv6 header will be addressed to the root. This case is identical
to the Storing mode case (see Section 7.2.3).
Table 27 summarizes which headers are needed for this use case.
+===========+=========+=========+============+=========+==========+
| Header | RUL src | 6LR_1 | 6LR_i | 6LBR | Internet |
| | | | i=(2,..,n) | | dst |
+===========+=========+=========+============+=========+==========+
| Added | -- | IP6-IP6 | -- | -- | -- |
| headers | | (RPI) | | | |
+===========+---------+---------+------------+---------+----------+
| Modified | -- | -- | RPI | -- | -- |
| headers | | | | | |
+===========+---------+---------+------------+---------+----------+
| Removed | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | (RPI) | |
+===========+---------+---------+------------+---------+----------+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+===========+---------+---------+------------+---------+----------+
Table 27: Non-SM: Summary of the Use of Headers from RUL to
Internet
8.2.4. Non-SM: Example of Flow from Internet to RUL
In this case, the flow comprises:
Internet src --> root (6LBR) --> 6LR_i --> RUL (IPv6 dst node)
For example, a communication flow could be: Internet --> Node A
(root) --> Node B --> Node E --> Node G
6LR_i represents the intermediate routers from the source to the
destination, and 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through, from the 6LBR to the RUL.
The 6LBR must add an RH3 header inside an IPv6-in-IPv6 header. The
6LBR will know the path and will recognize that the final node is not
a RPL-capable node as it will have received the connectivity DAO from
the nearest 6LR. The 6LBR can therefore make the IPv6-in-IPv6 header
destination be the last 6LR. The 6LBR will set to zero the flow
label upon entry in order to aid compression [RFC8138].
Table 28 summarizes which headers are needed for this use case.
+===========+==========+============+============+============+=====+
| Header | Internet | 6LBR | 6LR_i | 6LR_n | RUL |
| | src | | | | dst |
+===========+==========+============+============+============+=====+
| Added | -- | IP6-IP6 | -- | -- | -- |
| headers | | (RH3, RPI) | | | |
+===========+----------+------------+------------+------------+-----+
| Modified | -- | -- | IP6-IP6 | -- | -- |
| headers | | | (RH3, RPI) | | |
+===========+----------+------------+------------+------------+-----+
| Removed | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | (RH3, | |
| | | | | RPI) | |
+===========+----------+------------+------------+------------+-----+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+===========+----------+------------+------------+------------+-----+
Table 28: Non-SM: Summary of the Use of Headers from Internet to RUL
8.3. Non-SM: Interaction between Leaves
This section describes the communication flow in Non-Storing mode
(Non-SM) between the following:
RAL to RAL
RAL to RUL
RUL to RAL
RUL to RUL
8.3.1. Non-SM: Example of Flow from RAL to RAL
In this case, the flow comprises:
RAL src --> 6LR_ia --> root (6LBR) --> 6LR_id --> RAL dst
For example, a communication flow could be: Node F (RAL src) --> Node
D --> Node B --> Node A (root) --> Node B --> Node E --> Node H (RAL
dst)
6LR_ia represents the intermediate routers from the source to the
root, and 1 <= ia <= n, where n is the total number of routers (6LR)
that the packet goes through, from the RAL to the root.
6LR_id represents the intermediate routers from the root to the
destination, and 1 <= id <= m, where m is the total number of the
intermediate routers (6LR).
This case involves only nodes in same RPL domain. The originating
node will add an RPI to the original packet and send the packet
Upward.
The originating node may put the RPI (RPI1) into an IPv6-in-IPv6
header addressed to the root so that the 6LBR can remove that header.
If it does not, then the RPI1 is forwarded down from the root in the
inner header to no avail.
The 6LBR will need to insert an RH3 header, which requires that it
add an IPv6-in-IPv6 header. It removes the RPI (RPI1), as it was
contained in an IPv6-in-IPv6 header addressed to it. Otherwise,
there may be an RPI buried inside the inner IP header, which should
be ignored. The root inserts an RPI (RPI2) alongside the RH3.
Networks that use the RPL point-to-point extension [RFC6997] are
essentially Non-Storing DODAGs and fall into this scenario or the
scenario given in Section 8.1.2, with the originating node acting as
a 6LBR.
Table 29 summarizes which headers are needed for this use case when
encapsulation to the root takes place.
Table 30 summarizes which headers are needed for this use case when
there is no encapsulation to the root. Note that in the Modified
headers row, going up in each 6LR_ia only the RPI1 is changed. Going
down, in each 6LR_id the IPv6 header is swapped with the RH3 so both
are changed alongside with the RPI2.
+===========+=========+========+===============+=========+=========+
| Header | RAL src | 6LR_ia | 6LBR | 6LR_id | RAL dst |
+===========+=========+========+===============+=========+=========+
| Added | IP6-IP6 | -- | IP6-IP6 (RH3 | -- | -- |
| headers | (RPI1) | | -> RAL, RPI2) | | |
+===========+---------+--------+---------------+---------+---------+
| Modified | -- | RPI1 | -- | IP6-IP6 | -- |
| headers | | | | (RH3, | |
| | | | | RPI2) | |
+===========+---------+--------+---------------+---------+---------+
| Removed | -- | -- | IP6-IP6 | -- | IP6-IP6 |
| headers | | | (RPI1) | | (RH3, |
| | | | | | RPI2) |
+===========+---------+--------+---------------+---------+---------+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+===========+---------+--------+---------------+---------+---------+
Table 29: Non-SM: Summary of the Use of Headers from RAL to RAL with
Encapsulation to the Root
+===========+======+========+=============+=============+===========+
| Header | RAL | 6LR_ia | 6LBR | 6LR_id | RAL dst |
| | src | | | | |
+===========+======+========+=============+=============+===========+
| Added | RPI1 | -- | IP6-IP6 | -- | -- |
| headers | | | (RH3, RPI2) | | |
+===========+------+--------+-------------+-------------+-----------+
| Modified | -- | RPI1 | -- | IP6-IP6 | -- |
| headers | | | | (RH3, | |
| | | | | RPI2) | |
+===========+------+--------+-------------+-------------+-----------+
| Removed | -- | -- | -- | -- | IP6-IP6 |
| headers | | | | | (RH3, |
| | | | | | RPI2) |
+===========+------+--------+-------------+-------------+-----------+
| Untouched | -- | -- | RPI1 | RPI1 | RPI1 |
| headers | | | | | (Ignored) |
+===========+------+--------+-------------+-------------+-----------+
Table 30: Non-SM: Summary of the Use of Headers from RAL to RAL
without Encapsulation to the Root
8.3.2. Non-SM: Example of Flow from RAL to RUL
In this case, the flow comprises:
RAL --> 6LR_ia --> root (6LBR) --> 6LR_id --> RUL (IPv6 dst node)
For example, a communication flow could be: Node F (RAL) --> Node D
--> Node B --> Node A (root) --> Node B --> Node E --> Node G (RUL)
6LR_ia represents the intermediate routers from the source to the
root, and 1 <= ia <= n, where n is the total number of intermediate
routers (6LR).
6LR_id represents the intermediate routers from the root to the
destination, and 1 <= id <= m, where m is the total number of the
intermediate routers (6LRs).
As in the previous case, the RAL (6LN) may insert an RPI (RPI1)
header, which must be in an IPv6-in-IPv6 header addressed to the root
so that the 6LBR can remove this RPI. The 6LBR will then insert an
RH3 inside a new IPv6-in-IPv6 header addressed to the last 6LR_id
(6LR_id = m) alongside the insertion of RPI2.
If the originating node does not put the RPI (RPI1) into an IPv6-in-
IPv6 header addressed to the root, then the RPI1 is forwarded down
from the root in the inner header to no avail.
Table 31 summarizes which headers are needed for this use case when
encapsulation to the root takes place. Table 32 summarizes which
headers are needed for this use case when no encapsulation to the
root takes place.
+===========+=========+========+=========+=========+=========+=====+
| Header | RAL src | 6LR_ia | 6LBR | 6LR_id | 6LR_m | RUL |
| | | | | | | dst |
+===========+=========+========+=========+=========+=========+=====+
| Added | IP6-IP6 | -- | IP6-IP6 | -- | -- | -- |
| headers | (RPI1) | | (RH3, | | | |
| | | | RPI2) | | | |
+===========+---------+--------+---------+---------+---------+-----+
| Modified | -- | RPI1 | -- | IP6-IP6 | -- | -- |
| headers | | | | (RH3, | | |
| | | | | RPI2) | | |
+===========+---------+--------+---------+---------+---------+-----+
| Removed | -- | -- | IP6-IP6 | -- | IP6-IP6 | -- |
| headers | | | (RPI1) | | (RH3, | |
| | | | | | RPI2) | |
+===========+---------+--------+---------+---------+---------+-----+
| Untouched | -- | -- | -- | -- | -- | -- |
| headers | | | | | | |
+===========+---------+--------+---------+---------+---------+-----+
Table 31: Non-SM: Summary of the Use of Headers from RAL to RUL with
Encapsulation to the Root
+===========+====+========+=========+=========+=========+===========+
| Header |RAL | 6LR_ia | 6LBR | 6LR_id | 6LR_n | RUL dst |
| |src | | | | | |
+===========+====+========+=========+=========+=========+===========+
| Added |RPI1| -- | IP6-IP6 | -- | -- | -- |
| headers | | | (RH3, | | | |
| | | | RPI2) | | | |
+===========+----+--------+---------+---------+---------+-----------+
| Modified | -- | RPI1 | -- | IP6-IP6 | -- | -- |
| headers | | | | (RH3, | | |
| | | | | RPI2) | | |
+===========+----+--------+---------+---------+---------+-----------+
| Removed | -- | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | | (RH3, | |
| | | | | | RPI2) | |
+===========+----+--------+---------+---------+---------+-----------+
| Untouched | -- | -- | RPI1 | RPI1 | RPI1 | RPI1 |
| headers | | | | | | (ignored) |
+===========+----+--------+---------+---------+---------+-----------+
Table 32: Non-SM: Summary of the Use of Headers from RAL to RUL
without Encapsulation to the Root
8.3.3. Non-SM: Example of Flow from RUL to RAL
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_ia --> root (6LBR) --> 6LR_id
--> RAL dst (6LN)
For example, a communication flow could be: Node G (RUL) --> Node E
--> Node B --> Node A (root) --> Node B --> Node E --> Node H (RAL)
6LR_ia represents the intermediate routers from source to the root,
and 1 <= ia <= n, where n is the total number of intermediate routers
(6LR).
6LR_id represents the intermediate routers from the root to the
destination, and 1 <= id <= m, where m is the total number of the
intermediate routers (6LR).
In this scenario, the RPI (RPI1) is added by the first 6LR (6LR_1)
inside an IPv6-in-IPv6 header addressed to the root. The 6LBR will
remove this RPI and add its own IPv6-in-IPv6 header containing an RH3
header and an RPI (RPI2).
Table 33 summarizes which headers are needed for this use case.
+===========+=====+=========+========+=========+=========+=========+
| Header | RUL | 6LR_1 | 6LR_ia | 6LBR | 6LR_id | RAL dst |
| | src | | | | | |
+===========+=====+=========+========+=========+=========+=========+
| Added | -- | IP6-IP6 | -- | IP6-IP6 | -- | -- |
| headers | | (RPI1) | | (RH3, | | |
| | | | | RPI2) | | |
+===========+-----+---------+--------+---------+---------+---------+
| Modified | -- | -- | RPI1 | -- | IP6-IP6 | -- |
| headers | | | | | (RH3, | |
| | | | | | RPI2) | |
+===========+-----+---------+--------+---------+---------+---------+
| Removed | -- | -- | -- | IP6-IP6 | -- | IP6-IP6 |
| headers | | | | (RPI1) | | (RH3, |
| | | | | | | RPI2) |
+===========+-----+---------+--------+---------+---------+---------+
| Untouched | -- | -- | -- | -- | -- | -- |
| headers | | | | | | |
+===========+-----+---------+--------+---------+---------+---------+
Table 33: Non-SM: Summary of the Use of Headers from RUL to RAL
8.3.4. Non-SM: Example of Flow from RUL to RUL
In this case, the flow comprises:
RUL (IPv6 src node) --> 6LR_1 --> 6LR_ia --> root (6LBR) --> 6LR_id
--> RUL (IPv6 dst node)
For example, a communication flow could be: Node G --> Node E -->
Node B --> Node A (root) --> Node C --> Node J
6LR_ia represents the intermediate routers from the source to the
root, and 1 <= ia <= n, where n is the total number of intermediate
routers (6LR).
6LR_id represents the intermediate routers from the root to the
destination, and 1 <= id <= m, where m is the total number of the
intermediate routers (6LR).
This scenario is the combination of the previous two cases.
Table 34 summarizes which headers are needed for this use case.
+===========+===+=========+=======+=========+=========+=========+===+
| Header |RUL| 6LR_1 | 6LR_ia| 6LBR | 6LR_id | 6LR_m |RUL|
| |src| | | | | |dst|
+===========+===+=========+=======+=========+=========+=========+===+
| Added | --| IP6-IP6 | -- | IP6-IP6 | -- | -- | --|
| headers | | (RPI1) | | (RH3, | | | |
| | | | | RPI2) | | | |
+===========+---+---------+-------+---------+---------+---------+---+
| Modified | --| -- | RPI1 | -- | IP6-IP6 | -- | --|
| headers | | | | | (RH3, | | |
| | | | | | RPI2) | | |
+===========+---+---------+-------+---------+---------+---------+---+
| Removed | --| -- | -- | IP6-IP6 | -- | IP6-IP6 | --|
| headers | | | | (RPI1) | | (RH3, | |
| | | | | | | RPI2) | |
+===========+---+---------+-------+---------+---------+---------+---+
| Untouched | --| -- | -- | -- | -- | -- | --|
| headers | | | | | | | |
+===========+---+---------+-------+---------+---------+---------+---+
Table 34: Non-SM: Summary of the Use of Headers from RUL to RUL
9. Operational Considerations of Supporting RULs
Roughly half of the situations described in this document involve
leaf ("host") nodes that do not speak RPL. These nodes fall into two
further categories: ones that drop a packet that have RPI or RH3
headers, and ones that continue to process a packet that has RPI and/
or RH3 headers.
[RFC8200] provides for new rules that suggest that nodes that have
not been configured (explicitly) to examine Hop-by-Hop Options
headers should ignore those headers and continue processing the
packet. Despite this, and despite the switch from 0x63 to 0x23,
there may be nodes that predate RFC 8200 or are simply intolerant.
Those nodes will drop packets that continue to have RPL artifacts in
them. In general, such nodes cannot be easily supported in RPL LLNs.
There are some specific cases where it is possible to remove the RPL
artifacts prior to forwarding the packet to the leaf host. The
critical thing is that the artifacts have been inserted by the RPL
root inside an IPv6-in-IPv6 header, and that the header has been
addressed to the 6LR immediately prior to the leaf node. In that
case, in the process of removing the IPv6-in-IPv6 header, the
artifacts can also be removed.
The above case occurs whenever traffic originates from the outside
the LLN (the "Internet" cases above), and Non-Storing mode is used.
In Non-Storing mode, the RPL root knows the exact topology (as it
must create the RH3 header) and therefore knows which 6LR is prior to
the leaf. For example, in Figure 3, Node E is the 6LR prior to leaf
Node G, or Node C is the 6LR prior to leaf Node J.
Traffic originating from the RPL root (such as when the data
collection system is co-located on the RPL root), does not require an
IPv6-in-IPv6 header (in Storing or Non-Storing mode), as the packet
is originating at the root, and the root can insert the RPI and RH3
headers directly into the packet as it is formed. Such a packet is
slightly smaller, but can only be sent to nodes (whether RPL aware or
not) that will tolerate the RPL artifacts.
An operator that finds itself with a high amount of traffic from the
RPL root to RPL-unaware leaves will have to do IPv6-in-IPv6
encapsulation if the leaf is not tolerant of the RPL artifacts. Such
an operator could otherwise omit this unnecessary header if it was
certain of the properties of the leaf.
As the Storing mode cannot know the final path of the traffic,
intolerant leaf nodes, which drop packets with RPL artifacts, cannot
be supported.
10. Operational Considerations of Introducing 0x23
This section describes the operational considerations of introducing
the new RPI Option Type of 0x23.
During bootstrapping, the node receives the DIO with the information
of RPI Option Type, indicating the new RPI in the DODAG Configuration
option flag. The DODAG root is in charge of configuring the current
network with the new value, through DIO messages, and determining
when all the nodes have been set with the new value. The DODAG
should change to a new DODAG version. In case of rebooting, the node
does not remember the RPI Option Type. Thus, the DIO is sent with a
flag indicating the new RPI Option Type.
The DODAG Configuration option is contained in a RPL DIO message,
which contains a unique Destination Advertisement Trigger Sequence
Number (DTSN) counter. The leaf nodes respond to this message with
DAO messages containing the same DTSN. This is a normal part of RPL
routing; the RPL root therefore knows when the updated DODAG
Configuration option has been seen by all nodes.
Before the migration happens, all the RPL-aware nodes should support
both values. The migration procedure is triggered when the DIO is
sent with the flag indicating the new RPI Option Type. Namely, it
remains at 0x63 until it is sure that the network is capable of 0x23,
then it abruptly changes to 0x23. The 0x23 RPI Option allows the
sending of packets to non-RPL nodes. The non-RPL nodes should ignore
the option and continue processing the packets.
As mentioned previously, indicating the new RPI in the DODAG
Configuration option flag is a way to avoid the flag day (abrupt
changeover) in a network using 0x63 as the RPI Option Type value. It
is suggested that RPL implementations accept both 0x63 and 0x23 RPI
Option Type values when processing the header to enable
interoperability.
11. IANA Considerations
11.1. Option Type in RPL Option
This document updates the registration made in the "Destination
Options and Hop-by-Hop Options" subregistry [RFC6553] from 0x63 to
0x23 as shown in Table 35.
+===========+===================+==============+===============+
| Hex Value | Binary Value | Description | Reference |
| +=====+=====+=======+ | |
| | act | chg | rest | | |
+===========+=====+=====+=======+==============+===============+
| 0x23 | 00 | 1 | 00011 | RPL Option | This document |
+-----------+-----+-----+-------+--------------+---------------+
| 0x63 | 01 | 1 | 00011 | RPL Option | [RFC6553], |
| | | | | (DEPRECATED) | this document |
+-----------+-----+-----+-------+--------------+---------------+
Table 35: Option Type in RPL Option
The "DODAG Configuration Option Flags for MOP 0..6" subregistry is
updated as follows (Table 36):
+============+========================+===============+
| Bit Number | Capability Description | Reference |
+============+========================+===============+
| 3 | RPI 0x23 enable | This document |
+------------+------------------------+---------------+
Table 36: DODAG Configuration Option Flag to
Indicate the RPI Flag Day
11.2. Change to the "DODAG Configuration Option Flags" Subregistry
IANA has changed the name of the "DODAG Configuration Option Flags"
subregistry to "DODAG Configuration Option Flags for MOP 0..6".
The subregistry references this document for this change.
11.3. Change MOP Value 7 to Reserved
IANA has changed the registration status of value 7 in the "Mode of
Operation" subregistry from Unassigned to Reserved. This change is
in support of future work.
This document is listed as a reference for this entry in the
subregistry.
12. Security Considerations
The security considerations covered in [RFC6553] and [RFC6554] apply
when the packets are in the RPL Domain.
The IPv6-in-IPv6 mechanism described in this document is much more
limited than the general mechanism described in [RFC2473]. The
willingness of each node in the LLN to decapsulate packets and
forward them could be exploited by nodes to disguise the origin of an
attack.
While a typical LLN may be a very poor origin for attack traffic (as
the networks tend to be very slow, and the nodes often have very low
duty cycles), given enough nodes, LLNs could still have a significant
impact, particularly if the attack is targeting another LLN.
Additionally, some uses of RPL involve large-backbone, ISP-scale
equipment [ACP], which may be equipped with multiple 100 Gb/s
interfaces.
Blocking or careful filtering of IPv6-in-IPv6 traffic entering the
LLN as described above will make sure that any attack that is mounted
must originate from compromised nodes within the LLN. The use of
network ingress filtering [BCP38] on egress traffic at the RPL root
will alert the operator to the existence of the attack as well as
drop the attack traffic. As the RPL network is typically numbered
from a single prefix, which is itself assigned by RPL, network
ingress filtering [BCP38] involves a single prefix comparison and
should be trivial to automatically configure.
There are some scenarios where IPv6-in-IPv6 traffic should be allowed
to pass through the RPL root, such as the IPv6-in-IPv6 mediated
communications between a new pledge and the Join Registrar/
Coordinator (JRC) when using [BRSKI] and [ZEROTOUCH-JOIN]. This is
the case for the RPL root to do careful filtering: it occurs only
when the Join Coordinator is not co-located inside the RPL root.
With the above precautions, an attack using IPv6-in-IPv6 tunnels can
only be by a node within the LLN on another node within the LLN.
Such an attack could, of course, be done directly. An attack of this
kind is meaningful only if the source addresses are either fake or if
the point is to amplify return traffic. Such an attack could also be
done without the use of IPv6-in-IPv6 headers, by using forged source
addresses instead. If the attack requires bidirectional
communication, then IPv6-in-IPv6 provides no advantages.
Whenever IPv6-in-IPv6 headers are being proposed, there is a concern
about creating security issues. In the Security Considerations
section of [RFC2473] (Section 9), it was suggested that tunnel entry
and exit points can be secured by securing the IPv6 path between
them. This recommendation is not practical for RPL networks.
[RFC5406] provides guidance on what on what additional details are
needed in order to "Use IPsec". While the use of Encapsulating
Security Payload (ESP) would prevent source address forgeries, in
order to use it with [RFC8138], compression would have to occur
before encryption, as the [RFC8138] compression is lossy. Once
encrypted, there would be no further redundancy to compress. These
are minor issues. The major issue is how to establish trust enough
such that Internet Key Exchange Protocol Version 2 (IKEv2) could be
used. This would require a system of certificates to be present in
every single node, including any Internet nodes that might need to
communicate with the LLN. Thus, using IPsec requires a global PKI in
the general case.
More significantly, the use of IPsec tunnels to protect the IPv6-in-
IPv6 headers would, in the general case, scale with the square of the
number of nodes. This is a lot of resources for a constrained nodes
on a constrained network. In the end, the IPsec tunnels would be
providing only BCP38-like origin authentication! That is, IPsec
provides a transitive guarantee to the tunnel exit point that the
tunnel entry point did network ingress filtering [BCP38] on traffic
going in. Just doing origin filtering per BCP 38 at the entry and
exit of the LLN provides a similar level of security without all the
scaling and trust problems related to IPv6 tunnels as discussed in
[RFC2473]. IPsec is not recommended.
An LLN with hostile nodes within it would not be protected against
impersonation within the LLN by entry/exit filtering.
The RH3 header usage described here can be abused in equivalent ways.
An external attacker may form a packet with an RH3 that is not fully
consumed and encapsulate it to hide the RH3 from intermediate nodes
and disguise the origin of traffic. As such, the attacker's RH3
header will not be seen by the network until it reaches the
destination, which will decapsulate it. As indicated in Section 4.2
of [RFC6554], RPL routers are responsible for ensuring that an SRH is
only used between RPL routers. As such, if there is an RH3 that is
not fully consumed in the encapsulated packet, the node that
decapsulates it MUST ensure that the outer packet was originated in
the RPL domain and drop the packet otherwise.
Also, as indicated by Section 2 of [RFC6554], RPL Border Routers "do
not allow datagrams carrying an SRH header to enter or exit a RPL
routing domain." This sentence must be understood as concerning non-
fully-consumed packets. A consumed (inert) RH3 header could be
present in a packet that flows from one LLN, crosses the Internet,
and enters another LLN. Per the discussion in this document, such
headers do not need to be removed. However, there is no case
described in this document where an RH3 is inserted in a Non-Storing
network on traffic that is leaving the LLN, but this document should
not preclude such a future innovation.
In short, a packet that crosses the border of the RPL domain MAY
carry an RH3, and if so, that RH3 MUST be fully consumed.
The RPI, if permitted to enter the LLN, could be used by an attacker
to change the priority of a packet by selecting a different
RPLInstanceID, perhaps one with a higher energy cost, for instance.
It could also be that not all nodes are reachable in an LLN using the
default RPLInstanceID, but a change of RPLInstanceID would permit an
attacker to bypass such filtering. Like the RH3, an RPI is to be
inserted by the RPL root on traffic entering the LLN by first
inserting an IPv6-in-IPv6 header. The attacker's RPI therefore will
not be seen by the network. Upon reaching the destination node, the
RPI has no further meaning and is just skipped; the presence of a
second RPI will have no meaning to the end node as the packet has
already been identified as being at its final destination.
For traffic leaving a RUL, if the RUL adds an uninitialized RPI
(e.g., with a value of zero), then the 6LR as a RPL Border Router
SHOULD rewrite the RPI to indicate the selected Instance and set the
flags. This is done in order to avoid the following scenarios: 1)
The leaf is an external router that passes a packet that it did not
generate and that carries an unrelated RPI, and 2) The leaf is an
attacker or presents misconfiguration and tries to inject traffic in
a protected Instance. Also, this applies to the case where the leaf
is aware of the RPL Instance and passes a correct RPI; the 6LR needs
a configuration that allows that leaf to inject in that instance.
The RH3 and RPIs could be abused by an attacker inside of the network
to route packets in nonobvious ways, perhaps eluding observation.
This usage appears consistent with a normal operation of [RFC6997]
and cannot be restricted at all. This is a feature, not a bug.
[RFC7416] deals with many other threats to LLNs not directly related
to the use of IPv6-in-IPv6 headers, and this document does not change
that analysis.
Nodes within the LLN can use the IPv6-in-IPv6 mechanism to mount an
attack on another part of the LLN, while disguising the origin of the
attack. The mechanism can even be abused to make it appear that the
attack is coming from outside the LLN, and unless countered, this
could be used to mount a DDOS attack upon nodes elsewhere in the
Internet. See [DDOS-KREBS] for an example of such attacks already
seen in the real world.
If an attack comes from inside of LLN, it can be alleviated with SAVI
(Source Address Validation Improvement) using [RFC8505] with
[RFC8928]. The attacker will not be able to source traffic with an
address that is not registered, and the registration process checks
for topological correctness. Notice that there is Layer 2
authentication in most of the cases. If an attack comes from outside
LLN, IPv6-in-IPv6 can be used to hide inner routing headers, but by
construction, the RH3 can typically only address nodes within the
LLN. That is, an RH3 with a CmprI less than 8 should be considered
an attack (see Section 3 of [RFC6554]).
Nodes outside of the LLN will need to pass IPv6-in-IPv6 traffic
through the RPL root to perform this attack. To counter, the RPL
root SHOULD either restrict ingress of IPv6-in-IPv6 packets (the
simpler solution), or it SHOULD walk the IP header extension chain
until it can inspect the upper-layer payload as described in
[RFC7045]. In particular, the RPL root SHOULD do network ingress
filtering [BCP38] on the source addresses of all IP headers that it
examines in both directions.
Note: there are some situations where a prefix will spread across
multiple LLNs via mechanisms such as the one described in [RFC8929].
In this case, the network ingress filtering [BCP38] needs to take
this into account, either by exchanging detailed routing information
on each LLN or by moving the network ingress filtering [BCP38]
further towards the Internet, so that the details of the multiple
LLNs do not matter.
13. References
13.1. Normative References
[BCP38] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, May 2000.
<https://rfc-editor.org/info/bcp38>
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6040] Briscoe, B., "Tunnelling of Explicit Congestion
Notification", RFC 6040, DOI 10.17487/RFC6040, November
2010, <https://www.rfc-editor.org/info/rfc6040>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<https://www.rfc-editor.org/info/rfc6553>.
[RFC6554] Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
Routing Header for Source Routes with the Routing Protocol
for Low-Power and Lossy Networks (RPL)", RFC 6554,
DOI 10.17487/RFC6554, March 2012,
<https://www.rfc-editor.org/info/rfc6554>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<https://www.rfc-editor.org/info/rfc7045>.
[RFC8025] Thubert, P., Ed. and R. Cragie, "IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Paging Dispatch",
RFC 8025, DOI 10.17487/RFC8025, November 2016,
<https://www.rfc-editor.org/info/rfc8025>.
[RFC8138] Thubert, P., Ed., Bormann, C., Toutain, L., and R. Cragie,
"IPv6 over Low-Power Wireless Personal Area Network
(6LoWPAN) Routing Header", RFC 8138, DOI 10.17487/RFC8138,
April 2017, <https://www.rfc-editor.org/info/rfc8138>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
13.2. Informative References
[ACP] Eckert, T., Behringer, M. H., and S. Bjarnason, "An
Autonomic Control Plane (ACP)", Work in Progress,
Internet-Draft, draft-ietf-anima-autonomic-control-plane-
30, 30 October 2020, <https://tools.ietf.org/html/draft-
ietf-anima-autonomic-control-plane-30>.
[BRSKI] Pritikin, M., Richardson, M. C., Eckert, T., Behringer, M.
H., and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", Work in Progress, Internet-
Draft, draft-ietf-anima-bootstrapping-keyinfra-45, 11
November 2020, <https://tools.ietf.org/html/draft-ietf-
anima-bootstrapping-keyinfra-45>.
[DDOS-KREBS]
Goodin, D., "Record-breaking DDoS reportedly delivered by
>145k hacked cameras", September 2016,
<https://arstechnica.com/information-technology/2016/09/
botnet-of-145k-cameras-reportedly-deliver-internets-
biggest-ddos-ever/>.
[RFC0801] Postel, J., "NCP/TCP transition plan", RFC 801,
DOI 10.17487/RFC0801, November 1981,
<https://www.rfc-editor.org/info/rfc801>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <https://www.rfc-editor.org/info/rfc2460>.
[RFC2473] Conta, A. and S. Deering, "Generic Packet Tunneling in
IPv6 Specification", RFC 2473, DOI 10.17487/RFC2473,
December 1998, <https://www.rfc-editor.org/info/rfc2473>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC5406] Bellovin, S., "Guidelines for Specifying the Use of IPsec
Version 2", BCP 146, RFC 5406, DOI 10.17487/RFC5406,
February 2009, <https://www.rfc-editor.org/info/rfc5406>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC6997] Goyal, M., Ed., Baccelli, E., Philipp, M., Brandt, A., and
J. Martocci, "Reactive Discovery of Point-to-Point Routes
in Low-Power and Lossy Networks", RFC 6997,
DOI 10.17487/RFC6997, August 2013,
<https://www.rfc-editor.org/info/rfc6997>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[RFC7416] Tsao, T., Alexander, R., Dohler, M., Daza, V., Lozano, A.,
and M. Richardson, Ed., "A Security Threat Analysis for
the Routing Protocol for Low-Power and Lossy Networks
(RPLs)", RFC 7416, DOI 10.17487/RFC7416, January 2015,
<https://www.rfc-editor.org/info/rfc7416>.
[RFC8180] Vilajosana, X., Ed., Pister, K., and T. Watteyne, "Minimal
IPv6 over the TSCH Mode of IEEE 802.15.4e (6TiSCH)
Configuration", BCP 210, RFC 8180, DOI 10.17487/RFC8180,
May 2017, <https://www.rfc-editor.org/info/rfc8180>.
[RFC8504] Chown, T., Loughney, J., and T. Winters, "IPv6 Node
Requirements", BCP 220, RFC 8504, DOI 10.17487/RFC8504,
January 2019, <https://www.rfc-editor.org/info/rfc8504>.
[RFC8505] Thubert, P., Ed., Nordmark, E., Chakrabarti, S., and C.
Perkins, "Registration Extensions for IPv6 over Low-Power
Wireless Personal Area Network (6LoWPAN) Neighbor
Discovery", RFC 8505, DOI 10.17487/RFC8505, November 2018,
<https://www.rfc-editor.org/info/rfc8505>.
[RFC8928] Thubert, P., Ed., Sarikaya, B., Sethi, M., and R. Struik,
"Address-Protected Neighbor Discovery for Low-Power and
Lossy Networks", RFC 8928, DOI 10.17487/RFC8928, November
2020, <https://www.rfc-editor.org/info/rfc8928>.
[RFC8929] Thubert, P., Ed., Perkins, C.E., and E. Levy-Abegnoli,
"IPv6 Backbone Router", RFC 8929, DOI 10.17487/RFC8929,
November 2020, <https://www.rfc-editor.org/info/rfc8929>.
[RFC9010] Thubert, P., Ed. and M. Richardson, "Routing for RPL
(Routing Protocol for Low-Power and Lossy Networks)
Leaves", RFC 9010, DOI 10.17487/RFC9010, April 2021,
<https://www.rfc-editor.org/rfc/rfc9010>.
[TUNNELS] Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", Work in Progress, Internet-Draft, draft-
ietf-intarea-tunnels-10, 12 September 2019,
<https://tools.ietf.org/html/draft-ietf-intarea-tunnels-
10>.
[ZEROTOUCH-JOIN]
Richardson, M., "6tisch Zero-Touch Secure Join protocol",
Work in Progress, Internet-Draft, draft-ietf-6tisch-
dtsecurity-zerotouch-join-04, 8 July 2019,
<https://tools.ietf.org/html/draft-ietf-6tisch-dtsecurity-
zerotouch-join-04>.
Acknowledgments
This work is done thanks to the grant given by the StandICT.eu
project.
A special BIG thanks to C. M. Heard for the help with Section 4.
Much of the editing in that section is based on his comments.
Additionally, the authors would like to acknowledge the review,
feedback, and comments of the following (in alphabetical order):
Dominique Barthel, Robert Cragie, Ralph Droms, Simon Duquennoy, Cenk
Guendogan, Rahul Jadhav, Benjamin Kaduk, Matthias Kovatsch, Gustavo
Mercado, Subramanian Moonesamy, Marcela Orbiscay, Cristian Perez,
Charlie Perkins, Alvaro Retana, Peter van der Stok, Xavier
Vilajosana, Éric Vyncke, and Thomas Watteyne.
Authors' Addresses
Maria Ines Robles
Universidad Tecno. Nac.(UTN)-FRM, Argentina /Aalto University Finland
Coronel Rodríguez 273
M5500 Mendoza
Provincia de Mendoza
Argentina
Email: mariainesrobles@gmail.com
Michael C. Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa ON K1Z 5V7
Canada
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/mcr/
Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
06254 MOUGINS - Sophia Antipolis
France
Phone: +33 497 23 26 34
Email: pthubert@cisco.com