Internet DRAFT - draft-ietf-roll-useofrplinfo
draft-ietf-roll-useofrplinfo
ROLL Working Group M. Robles
Internet-Draft UTN-FRM/Aalto
Updates: 6553, 6550, 8138 (if approved) M. Richardson
Intended status: Standards Track SSW
Expires: July 19, 2021 P. Thubert
Cisco
January 15, 2021
Using RPI Option Type, Routing Header for Source Routes and IPv6-in-IPv6
encapsulation in the RPL Data Plane
draft-ietf-roll-useofrplinfo-44
Abstract
This document looks at different data flows through LLN (Low-Power
and Lossy Networks) where RPL (IPv6 Routing Protocol for Low-Power
and Lossy Networks) is used to establish routing. The document
enumerates the cases where RFC6553 (RPI Option Type), RFC6554
(Routing Header for Source Routes) and IPv6-in-IPv6 encapsulation is
required in data plane. This analysis provides the basis on which to
design efficient compression of these headers. This document updates
RFC6553 adding a change to the RPI Option Type. Additionally, this
document updates RFC6550 defining a flag in the DIO Configuration
option to indicate about this change and updates RFC8138 as well to
consider the new Option Type when the RPL Option is decompressed.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 19, 2021.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology and Requirements Language . . . . . . . . . . . . 5
3. RPL Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Updates to RFC6550, RFC6553 and RFC8138 . . . . . . . . . . . 7
4.1. Updates to RFC6550 . . . . . . . . . . . . . . . . . . . 7
4.1.1. Advertising External Routes with Non-Storing Mode
Signaling. . . . . . . . . . . . . . . . . . . . . . 7
4.1.2. Configuration Options and Mode
of Operation . . . . . . . . . . . . . . . . . . . . 8
4.1.3. Indicating the new RPI in the
DODAG Configuration option Flag. . . . . . . . . . . 9
4.2. Updates to RFC6553: Indicating the new RPI Option Type. . 10
4.3. Updates to RFC8138: Indicating the way to decompress with
the new RPI Option Type. . . . . . . . . . . . . . . . . 13
5. Sample/reference topology . . . . . . . . . . . . . . . . . . 14
6. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 16
7. Storing mode . . . . . . . . . . . . . . . . . . . . . . . . 19
7.1. Storing Mode: Interaction between Leaf and Root . . . . . 20
7.1.1. SM: Example of Flow from RAL to Root . . . . . . . . 21
7.1.2. SM: Example of Flow from Root to RAL . . . . . . . . 22
7.1.3. SM: Example of Flow from Root to RUL . . . . . . . . 22
7.1.4. SM: Example of Flow from RUL to Root . . . . . . . . 24
7.2. SM: Interaction between Leaf and Internet. . . . . . . . 25
7.2.1. SM: Example of Flow from RAL to Internet . . . . . . 25
7.2.2. SM: Example of Flow from Internet to RAL . . . . . . 27
7.2.3. SM: Example of Flow from RUL to Internet . . . . . . 28
7.2.4. SM: Example of Flow from Internet to RUL. . . . . . . 29
7.3. SM: Interaction between Leaf and Leaf . . . . . . . . . . 30
7.3.1. SM: Example of Flow from RAL to RAL . . . . . . . . . 30
7.3.2. SM: Example of Flow from RAL to RUL . . . . . . . . . 31
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7.3.3. SM: Example of Flow from RUL to RAL . . . . . . . . . 33
7.3.4. SM: Example of Flow from RUL to RUL . . . . . . . . . 34
8. Non Storing mode . . . . . . . . . . . . . . . . . . . . . . 35
8.1. Non-Storing Mode: Interaction between Leaf and Root . . . 37
8.1.1. Non-SM: Example of Flow from RAL to root . . . . . . 37
8.1.2. Non-SM: Example of Flow from root to RAL . . . . . . 38
8.1.3. Non-SM: Example of Flow from root to RUL . . . . . . 39
8.1.4. Non-SM: Example of Flow from RUL to root . . . . . . 40
8.2. Non-Storing Mode: Interaction between Leaf and Internet . 41
8.2.1. Non-SM: Example of Flow from RAL to Internet . . . . 41
8.2.2. Non-SM: Example of Flow from Internet to RAL . . . . 43
8.2.3. Non-SM: Example of Flow from RUL to Internet . . . . 44
8.2.4. Non-SM: Example of Flow from Internet to RUL . . . . 45
8.3. Non-SM: Interaction between leaves . . . . . . . . . . . 46
8.3.1. Non-SM: Example of Flow from RAL to RAL . . . . . . . 46
8.3.2. Non-SM: Example of Flow from RAL to RUL . . . . . . . 49
8.3.3. Non-SM: Example of Flow from RUL to RAL . . . . . . . 51
8.3.4. Non-SM: Example of Flow from RUL to RUL . . . . . . . 52
9. Operational Considerations of supporting
RUL-leaves . . . . . . . . . . . . . . . . . . . . . . . . . 53
10. Operational considerations of introducing 0x23 . . . . . . . 54
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 54
11.1. Option Type in RPL Option . . . . . . . . . . . . . . . 54
11.2. Change to the DODAG Configuration Options Flags registry 55
11.3. Change MOP value 7 to Reserved . . . . . . . . . . . . . 55
12. Security Considerations . . . . . . . . . . . . . . . . . . . 56
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 59
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 59
14.1. Normative References . . . . . . . . . . . . . . . . . . 60
14.2. Informative References . . . . . . . . . . . . . . . . . 61
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 63
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 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) though the RPI is the routing
information that is defined in [RFC6550] and transported in the RPL
Option. RFC6554 [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
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traffic at all which is mostly Hop-by-Hop traffic (one exception
being 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 WG analyzed how [RFC2460] rules apply to 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 [RFC8200] routers ignore this option
when not recognized.
A Routing Header Dispatch for 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, [I-D.ietf-intarea-tunnels] is recommended reading to
explain the relationship of IP tunnels to existing protocol layers
and the challenges in supporting IP tunneling.
Non-constrained uses of RPL are not in scope of this document, and
applicability statements for those uses may provide different advice,
E.g. [I-D.ietf-anima-autonomic-control-plane].
1.1. Overview
The rest of the document is organized as follows: Section 2 describes
the used terminology. Section 3 provides a RPL Overview. Section 4
describes the updates to RFC6553, RFC6550 and RFC 8138. Section 5
provides the reference topology used for the uses 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.
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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.
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 header. It results that 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 Header.
[RFC8138] provides an alternate (more compressed) formating for the
same abstract information.
RPL-aware-node (RAN): A device which 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 which does not implement RPL, thus the
device is not-RPL-aware. 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: "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.
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6LoWPAN Router (6LR): [RFC6775] defines it as:" 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:"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 can not communicate
with nodes running the new configuration. For instance, 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) and 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): 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): 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 figures (tables) we refer to IPv6-
in-IPv6 as IP6-IP6.
3. RPL Overview
RPL defines the RPL Control messages (control plane), a new ICMPv6
[RFC4443] message with Type 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.
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+--------------+
| 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 a 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-storing-mode messaging even in a storing mode
network, see Section 4.1.1
4. Updates to RFC6550, RFC6553 and RFC8138
4.1. Updates to RFC6550
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 [RFC8138] compression 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
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compression should be expanded by the 6LR before it forwards a packet
outside the RPL domain.
This specification updates [RFC6550] to RECOMMEND that external
targets are advertised using Non-Storing Mode DAO messaging even in a
Storing-Mode network. 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 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 unless it is aware
that the RUL supports IP-in-IP decapsulation.
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 uncompress 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 DODAG Configuration
Option Flags registry so that it applies to Mode of Operation (MOP)
values zero (0) to six (6) only, leaving the flags unassigned for MOP
value seven (7).The MOP is described in RFC6550 section 6.3.1.
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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
new RPI Option Type (0x23) and old RPI Option Type (0x63) nodes, this
section defines a flag in the DIO Configuration option, to indicate
when the new RPI Option Type can be safely used. This means, 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 which 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 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: "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 in RFC6553
Compatible Mode; originating traffic with the old-RPI Option Type
(0x63) value. 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 flag field in the DODAG Configuration option
is to be used as shown in Figure 2 (which is the same as Figure 39 in
Section 11 and is shown here for convenience):
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+------------+-----------------+---------------+
| Bit number | Description | Reference |
+------------+-----------------+---------------+
| 3 | RPI 0x23 enable | This document |
+------------+-----------------+---------------+
Figure 2: 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
indicating the RPI value to be used. The node will use the value
0x23 if the network supports this feature.
4.2. Updates to RFC6553: 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 Internet (see Section 7.2.1), without requiring IPv6-in-IPv6
encapsulation.
[RFC6553] (Section 6, Page 7) states as shown in Figure 3, 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 | Binary Value | Description | Reference |
+ Value +-------------------+ + +
| | act | chg | rest | | |
+-------+-----+-----+-------+----------------+-----------+
| 0x63 | 01 | 1 | 00011 | RPL Option | [RFC6553] |
+-------+-----+-----+-------+----------------+-----------+
Figure 3: Option Type in RPL Option.
This document illustrates that it is not always possible to know for
sure at the source that a packet will only travel within the RPL
domain or may leave it.
At the time [RFC6553] was published, leaking a Hop-by-Hop 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
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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, 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 intention was and remains that the Hop-by-Hop 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 behaviour 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. But with
the current value of the Option Type, if a node in the Internet is
configured to process the Hop-by-Hop header, and if such node
encounters an option with the first two bits set to 01 and 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, to (Figure 4):
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-not-
capable) receives a packet with a RPL Option, it should ignore the
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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 | Binary Value | Description | Reference |
+ Value +-------------------+ + +
| | act | chg | rest | | |
+-------+-----+-----+-------+-------------+------------+
| 0x23 | 00 | 1 | 00011 | RPL Option |[RFCXXXX](*)|
+-------+-----+-----+-------+-------------+------------+
Figure 4: Revised Option Type in RPL Option. (*)represents this
document
Without the signaling described below, this change would otherwise
create a lack of interoperation (flag day) for existing networks
which 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 DIO Configuration option (Section Section 4.1.3).
The change of RPI Option Type from 0x63 to 0x23, makes all [RFC8200]
Section 4.2 compliant nodes 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.
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In the non-storing case, dealing with not-RPL aware 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 not-RPL aware leaf nodes because it will
receive a DAO about that node from the 6LR immediately above that
not-RPL aware 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 RFC8138: 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.
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. E.g. If the network
is in 0x23 mode (by DIO option), then it should be decompressed to
0x23.
[RFC8138] section 7 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 use of the IPv6-in-IPv6 header is MANDATORY in this
case, and it SHOULD be compressed with [RFC8138] section 7. Figure 5
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.
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+-+ ... -+-+ ... +-+- ... -+-+- +-+-+-+ ... +-+-+ ... -+++ ... +-...
|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 5: RPI Inserted by the Root in Storing Mode
In Figure 5, 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 an SRH-6LoRH as the
first 6LoRH. There is a single entry so the SRH-6LoRH Size is 0. In
that example, the type is 1 so the 6LR address is compressed to 2
bytes. It results that the total length of the SRH-6LoRH is 4 bytes.
Follows the RPI-6LoRH and then the IP-in-IP 6LoRH. 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. Sample/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 6 shows the reference RPL Topology for this document. The
letters above the nodes are there 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 (RAL) marked as (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 (not-RPL-aware), but use Router-Advertisements, 6LowPAN DAR/
DAC and 6LoWPAN 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.
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+------------+
| 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 6: A reference RPL Topology.
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6. Use cases
In the data plane a combination of RFC6553, RFC6554 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].
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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). This sometimes can result in outer IP headers being
addressed to the next hop router using link-local address.
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 AH
security header can be applied across these headers, but it can not
secure the values which 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
[I-D.ietf-anima-autonomic-control-plane].
Throughout the following subsections, the examples are described in
more details in the first subsections, and more concisely in the
later ones.
The uses cases are delineated based on the following IPV6 and RPL
mandates:
The RPI has to be in every packet that traverses the LLN.
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- 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.
- Non-storing mode requires downstream encapsulation by root for
RH3.
The uses 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 0x23 RPI Option Type can be safely inserted.
- All 6LRs obey [RFC8200].
- The RPI is ignored at the IPv6 dst node (RUL).
- In the uses cases, we assume that the RAL supports IP-in-IP
encapsulation.
- In the uses 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.
- Non-constrained uses of RPL are not in scope of this document.
- Compression is based on [RFC8138].
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- 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.
The following table (Figure 7) itemizes which headers are needed in
each of the following scenarios. It indicates whether an IPv6-in-
IPv6 header must be added and what destination it must be addressed
to: (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 (Figure 11).
The leaf can be a router 6LR or a host, both indicated as 6LN. The
root refers to the 6LBR (see Figure 6).
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+---------------------+--------------+------------+----------------+
| Interaction between | Use Case |IPv6-in-IPv6|IPv6-in-IPv6 dst|
+---------------------+--------------+------------+----------------+
| | RAL to root | No | N/A |
+ +--------------+------------+----------------+
| Leaf - Root | root to RAL | No | N/A |
+ +--------------+------------+----------------+
| | root to RUL | must | 6LR |
+ +--------------+------------+----------------+
| | RUL to root | must | root |
+---------------------+--------------+------------+----------------+
| | RAL to Int | may | root |
+ +--------------+------------+----------------+
| Leaf - Internet | Int to RAL | must | RAL (tgt) |
+ +--------------+------------+----------------+
| | RUL to Int | must | root |
+ +--------------+------------+----------------+
| | Int to RUL | must | 6LR |
+---------------------+--------------+------------+----------------+
| | RAL to RAL | No | N/A |
| Leaf - Leaf +--------------+------------+----------------+
| | RAL to RUL | No(up) | N/A |
| + +------------+----------------+
| | | must(down) | 6LR |
| +--------------+------------+----------------+
| | RUL to RAL | must(up) | root |
| | +------------+----------------+
| | | must(down) | RAL |
| +--------------+------------+----------------+
| | RUL to RUL | must(up) | root |
| | +------------+----------------+
| | | must(down) | 6LR |
|---------------------+--------------+------------+----------------+
Figure 7: Table of IPv6-in-IPv6 encapsulation in Storing mode.
7.1. Storing Mode: Interaction between Leaf and Root
In this section is described the communication flow in storing mode
(SM) between,
RAL to root
root to RAL
RUL to root
root to RUL
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7.1.1. SM: Example of Flow from RAL to Root
In storing mode, RFC 6553 (RPI) is used to send RPL Information
instanceID 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 6LR (Node
D) which decrements the rank in the RPI and sends the packet up.
When the packet arrives at 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.
The Figure 8 summarizes what headers are needed for this use case.
+-----------+-----+-------+------+
| Header | RAL | 6LR_i | 6LBR |
| | src | | dst |
+-----------+-----+-------+------+
| Added | RPI | -- | -- |
| headers | | | |
+-----------+-----+-------+------+
| Modified | -- | RPI | -- |
| headers | | | |
+-----------+-----+-------+------+
| Removed | -- | -- | RPI |
| headers | | | |
+-----------+-----+-------+------+
| Untouched | -- | -- | -- |
| headers | | | |
+-----------+-----+-------+------+
Figure 8: SM: Summary of the use of headers from RAL to root
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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
is going to increment the rank in RPI (it examines the RPLInstanceID
to identify the right forwarding table), the packet is processed in
the RAL and the RPI removed.
No IPv6-in-IPv6 header is required.
The Figure 9 summarizes what headers are needed for this use case.
+-----------+------+-------+-----+
| Header | 6LBR | 6LR_i | RAL |
| | src | | dst |
+-----------+------+-------+-----+
| Added | RPI | -- | -- |
| headers | | | |
+-----------+------+-------+-----+
| Modified | -- | RPI | -- |
| headers | | | |
+-----------+------+-------+-----+
| Removed | -- | -- | RPI |
| headers | | | |
+-----------+------+-------+-----+
| Untouched | -- | -- | -- |
| headers | | | |
+-----------+------+-------+-----+
Figure 9: 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), 1 <= i <= n, where n is the total
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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.
The Figure 10 summarizes what headers are needed for this use case.
+-----------+---------+---------+---------+-----+
| Header | 6LBR | 6LR_i | 6LR_n | RUL |
| | src | | | dst |
+-----------+---------+---------+---------+-----+
| Added | IP6-IP6 | -- | -- | -- |
| headers | RPI | | | |
+-----------+---------+---------+---------+-----+
| Modified | -- | | -- | -- |
| headers | | RPI | | |
+-----------+---------+---------+---------+-----+
| Removed | -- | -- | IP6-IP6 | -- |
| headers | | | RPI | |
+-----------+---------+---------+---------+-----+
| Untouched | -- | IP6-IP6 | -- | -- |
| headers | | | | |
+-----------+---------+---------+---------+-----+
Figure 10: 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.
The Figure 11 summarizes what headers are needed for this scenario.
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+-----------+----------+--------------+----------------+----------+
| Header | 6LBR | 6LR_i | 6LR_n | RUL |
| | src | i=(1,..,n-1) | | dst |
| | | | | |
+-----------+----------+--------------+----------------+----------+
| Added | RPI, RH3 | -- | -- | -- |
| headers | | | | |
+-----------+----------+--------------+----------------+----------+
| Modified | -- | RPI | RPI | -- |
| headers | | | RH3(consumed) | |
+-----------+----------+--------------+----------------+----------+
| Removed | -- | -- | -- | -- |
| headers | | | | |
+-----------+----------+--------------+----------------+----------+
| Untouched | -- | RH3 | -- | RPI, RH3 |
| headers | | | | (both |
| | | | | ignored) |
+-----------+----------+--------------+----------------+----------+
Figure 11: 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), 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.
The Figure 12 shows the table that summarizes what headers are needed
for this use case where the IPv6-in-IPv6 header is addressed to the
root (Node A).
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+-----------+------+--------------+----------------+-----------------+
| Header | RUL | 6LR_1 | 6LR_i | 6LBR dst |
| | src | | | |
| | node | | | |
+-----------+------+--------------+----------------+-----------------+
| Added | -- | IP6-IP6 | | -- |
| headers | | RPI | -- | |
+-----------+------+--------------+----------------+-----------------+
| Modified | -- | -- | RPI | -- |
| headers | | | | |
+-----------+------+--------------+----------------+-----------------+
| Removed | -- | -- | --- | IP6-IP6 |
| headers | | | | RPI |
+-----------+------+--------------+----------------+-----------------+
| Untouched | -- | -- | IP6-IP6 | -- |
| headers | | | | |
+-----------+------+--------------+----------------+-----------------+
Figure 12: SM: Summary of the use of headers from RUL to root.
7.2. SM: Interaction between Leaf and Internet.
In this section is described the communication flow in storing mode
(SM) between,
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), 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through from the RAL to the 6LBR.
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RPL information from RFC 6553 may go out to Internet as it will be
ignored by nodes which have not been configured to be RPI aware. No
IPv6-in-IPv6 header is required.
On the other hand, the RAL may insert the RPI encapsulated in a IPv6-
in-IPv6 header to the root. Thus, the root removes the RPI and send
the packet to the Internet.
Note: In this use case, it is used a node as a leaf, but this use
case can be also applicable to any RPL-aware-node type (e.g. 6LR)
The Figure 13 summarizes what 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 case that it is not already
zero. The Figure 14 summarizes what headers are needed when
encapsulation to the root takes place.
+-----------+-----+-------+------+-----------+
| Header | RAL | 6LR_i | 6LBR | Internet |
| | src | | | dst |
+-----------+-----+-------+------+-----------+
| Added | RPI | -- | -- | -- |
| headers | | | | |
+-----------+-----+-------+------+-----------+
| Modified | -- | RPI | RPI | -- |
| headers | | | | |
+-----------+-----+-------+------+-----------+
| Removed | -- | -- | -- | -- |
| headers | | | | |
+-----------+-----+-------+------+-----------+
| Untouched | -- | -- | -- | RPI |
| headers | | | | (Ignored) |
+-----------+-----+-------+------+-----------+
Figure 13: SM: Summary of the use of headers from RAL to Internet
with no encapsulation
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+-----------+----------+--------------+--------------+--------------+
| Header | RAL | 6LR_i | 6LBR | Internet dst |
| | src | | | |
+-----------+----------+--------------+--------------+--------------+
| Added | IP6-IP6 | -- | -- | -- |
| headers | RPI | | | |
+-----------+----------+--------------+--------------+--------------+
| Modified | -- | RPI | -- | -- |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
| Removed | -- | -- | IP6-IP6 | -- |
| headers | | | RPI | |
+-----------+----------+--------------+--------------+--------------+
| Untouched | -- | IP6-IP6 | -- | -- |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
Figure 14: 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 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.
The Figure 15 shows the table that summarizes what headers are needed
for this use case.
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+-----------+----------+--------------+--------------+--------------+
| Header | Internet | 6LBR | 6LR_i | RAL dst |
| | src | | | |
+-----------+----------+--------------+--------------+--------------+
| Added | -- | IP6-IP6(RPI) | -- | -- |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
| Modified | -- | -- | RPI | -- |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
| Removed | -- | -- | -- | IP6-IP6(RPI) |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
Figure 15: 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].
The Figure 16 shows the table that summarizes what headers are needed
for this use case.
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+---------+-------+------------+-------------+-------------+--------+
| Header | IPv6 | 6LR_1 | 6LR_i | 6LBR |Internet|
| | src | | [i=2,...,n] | | dst |
| | node | | | | |
| | (RUL) | | | | |
+---------+-------+------------+-------------+-------------+--------+
| Added | -- |IP6-IP6(RPI)| -- | -- | -- |
| headers | | | | | |
+---------+-------+------------+-------------+-------------+--------+
| Modified| -- | -- | RPI | -- | -- |
| headers | | | | | |
+---------+-------+------------+-------------+-------------+--------+
| Removed | -- | -- | -- | IP6-IP6(RPI)| -- |
| headers | | | | | |
+---------+-------+------------+-------------+-------------+--------+
|Untouched| -- | -- | -- | -- | -- |
| headers | | | | | |
+---------+-------+------------+-------------+-------------+--------+
Figure 16: 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 is addressed to the 6LR parent of the RUL.
Further details about this are mentioned in
[I-D.ietf-roll-unaware-leaves], which specifies RPL routing for a 6LN
acting as a plain host and not being aware 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].
The Figure 17 shows the table that summarizes what headers are needed
for this use case.
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+---------+-------+------------+--------------+-------------+-------+
| Header |Inter- | 6LBR | 6LR_i | 6LR_n | RUL |
| | net | |[i=1,..,n-1] | | dst |
| | src | | | | |
| | | | | | |
+---------+-------+------------+--------------+-------------+-------+
| Inserted| -- |IP6-IP6(RPI)| -- | -- | -- |
| headers | | | | | |
+---------+-------+------------+--------------+-------------+-------+
| Modified| -- | -- | RPI | -- | -- |
| headers | | | | | |
+---------+-------+------------+--------------+-------------+-------+
| Removed | -- | -- | -- | IP6-IP6(RPI)| -- |
| headers | | | | | |
+---------+-------+------------+--------------+-------------+-------+
|Untouched| -- | -- | -- | -- | -- |
| headers | | | | | |
+---------+-------+------------+--------------+-------------+-------+
Figure 17: SM: Summary of the use of headers from Internet to RUL.
7.3. SM: Interaction between Leaf and Leaf
In this section is described the communication flow in storing mode
(SM) between,
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 in
[RFC6550].
When the nodes are not directly connected, then in storing mode, the
flow comprises:
RAL src (6LN) --> 6LR_ia --> common parent (6LR_x) --> 6LR_id --> RAL
dst (6LN)
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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 source to
the common parent (6LR_x) (Node B), 1 <= ia <= n, where n is the
total number of routers (6LR) that the packet goes through from 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 destination RAL (Node H), 1 <= id <= m,
where m is the total number of routers (6LR) that the packet goes
through from the common parent (6LR_x) to 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.
The Figure 18 summarizes what headers are needed for this use case.
+-----------+-----+--------+---------+--------+-----+
| Header | RAL | 6LR_ia | 6LR_x | 6LR_id | RAL |
| | src | | (common | | dst |
| | | | parent) | | |
+-----------+-----+--------+---------+--------+-----+
| Added | RPI | -- | -- | -- | -- |
| headers | | | | | |
+-----------+-----+--------+---------+--------+-----+
| Modified | -- | RPI | RPI | RPI | -- |
| headers | | | | | |
+-----------+-----+--------+---------+--------+-----+
| Removed | -- | -- | -- | -- | RPI |
| headers | | | | | |
+-----------+-----+--------+---------+--------+-----+
| Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+-----------+-----+--------+---------+--------+-----+
Figure 18: 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:
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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 source (RAL) to the
common parent (the Root), 1 <= ia <= n, where n is the total number
of routers (6LR) that the packet goes through from RAL to the Root.
6LR_id (Node E) represents the intermediate routers from the Root
(Node B) to 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 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-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.
The Figure 19 summarizes what headers are needed for this use case.
+----------+-------+-------+---------+---------+---------+---------+
| Header | RAL |6LR_ia | 6LBR | 6LR_id | 6LR_m | RUL |
| | src | | | | | dst |
| | node | | | | | node |
+----------+-------+-------+---------+---------+---------+---------+
| Added | | | IP6-IP6 | -- | -- | -- |
| headers | RPI1 | -- | (RPI2) | | | |
| | | | | | | |
+----------+-------+-------+---------+---------+---------+---------+
| Modified | -- | | -- | | | -- |
| headers | | RPI1 | | RPI2 | -- | |
| | | | | | | |
+----------+-------+-------+---------+---------+---------+---------+
| Removed | -- | -- | | -- | IP6-IP6 | -- |
| headers | | | -- | | (RPI2) | |
| | | | | | | |
+----------+-------+-------+---------+---------+---------+---------+
|Untouched | -- | -- | RPI1 | RPI1 | RPI1 | RPI1 |
| headers | | | | | |(Ignored)|
| | | | | | | |
+----------+-------+-------+---------+---------+---------+---------+
Figure 19: SM: Summary of the Use of Headers from RAL to RUL
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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 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 source to the root.
6LR_id represents the intermediate routers from the root (Node A) to
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 a 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).
The Figure 20 shows the table that summarizes what headers are needed
for this use case.
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+-----------+------+---------+---------+---------+---------+---------+
| Header | RUL | 6LR_1 | 6LR_ia | 6LBR | 6LR_id | RAL |
| | src | | | | | dst |
| | node | | | | | node |
+-----------+------+---------+---------+---------+---------+---------+
| Added | -- | IP6-IP6 | -- | IP6-IP6 | -- | -- |
| headers | | (RPI1) | | (RPI2) | | |
| | | | | | | |
+-----------+------+---------+---------+---------+---------+---------+
| Modified | -- | | | -- | | -- |
| headers | | -- | RPI1 | | RPI2 | |
| | | | | | | |
+-----------+------+---------+---------+---------+---------+---------+
| Removed | -- | | -- | IP6-IP6 | -- | IP6-IP6 |
| headers | | -- | | (RPI1) | | (RPI2) |
| | | | | | | |
+-----------+------+---------+---------+---------+---------+---------+
| Untouched | -- | -- | -- | -- | -- | -- |
| headers | | | | | | |
+-----------+------+---------+---------+---------+---------+---------+
Figure 20: 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 refers
when ia=1.
6LR_id (Node C) represents the intermediate routers from the root
(Node A) to the destination RUL dst node (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 destination RUL.
The 6LR_1 (Node E) receives the packet from the RUL (Node G) and
inserts the RPI (RPI), encapsulated in an IPv6-in-IPv6 header
directed to the root. The root removes the outer header including
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the RPI (RPI1) and inserts a new RPI (RPI2) addressed to the 6LR
father of the RUL.
The Figure 21 shows the table that summarizes what headers are needed
for this use case.
+---------+----+-------------+--------+---------+--------+-------+---+
| Header |RUL | 6LR_1 | 6LR_ia | 6LBR | 6LR_id |6LR_n |RUL|
| |src | | | | | |dst|
| | | | | | | | |
+---------+----+-------------+--------+---------+--------+-------+---+
| Added | -- |IP6-IP6(RPI1)| -- | IP6-IP6 | -- | -- | --|
| Headers | | | | (RPI2) | | | |
+---------+----+-------------+--------+---------+--------+-------+---+
|Modified | -- | -- | | -- | | -- | --|
|headers | | | RPI1 | | RPI2 | | |
+---------+----+-------------+--------+---------+--------+-------+---+
| Removed | -- | -- | -- | IP6-IP6 | -- |IP6-IP6| --|
| headers | | | | (RPI1) | | (RPI2)| |
+---------+----+-------------+--------+---------+--------+-------+---+
|Untouched| -- | -- | -- | -- | -- | -- | --|
| headers | | | | | | | |
+---------+----+-------------+--------+---------+--------+-------+---+
Figure 21: 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
not-RPL aware receivers.
The table (Figure 22) summarizes what 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 upwards direction. The term
"must(up)" means that the IPv6-in-IPv6 header must be present in the
upwards direction. The term "must(down)" means that the IPv6-in-IPv6
header must be present in the downward direction.
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The leaf can be a router 6LR or a host, both indicated as 6LN
(Figure 6). In the table (Figure 22) 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 Case | RPI | RH3 | IPv6-in-IPv6 | IP-in-IP |
| between | | | | | dst |
+----------------+-------------+-----+-----+--------------+----------+
| | RAL to root | Yes | No | No | No |
| +-------------+-----+-----+--------------+----------+
| Leaf - Root | root to RAL | Yes | Yes | No | No |
| +-------------+-----+-----+--------------+----------+
| | root to RUL | Yes | Yes | No | 6LR |
| | | (1) | | | |
| +-------------+-----+-----+--------------+----------+
| | RUL to root | Yes | No | must | root |
+----------------+-------------+-----+-----+--------------+----------+
| | RAL to Int | Yes | No | may(up) | root |
| +-------------+-----+-----+--------------+----------+
|Leaf - Internet | Int to RAL | Yes | Yes | must | RAL |
| +-------------+-----+-----+--------------+----------+
| | RUL to Int | Yes | No | must | root |
| +-------------+-----+-----+--------------+----------+
| | Int to RUL | Yes | Yes | must | 6LR |
+----------------+-------------+-----+-----+--------------+----------+
| | RAL to RAL | Yes | Yes | may(up) | root |
| | | | +--------------+----------+
| | | | | must(down) | RAL |
| Leaf - Leaf +-------------+-----+-----+--------------+----------+
| | RAL to RUL | Yes | Yes | may(up) | root |
| | | | +--------------+----------+
| | | | | must(down) | 6LR |
| +-------------+-----+-----+--------------+----------+
| | RUL to RAL | Yes | Yes | must(up) | root |
| | | | +--------------+----------+
| | | | | must(down) | RAL |
| +-------------+-----+-----+--------------+----------+
| | RUL to RUL | Yes | Yes | must(up) | root |
| | | | +--------------+----------+
| | | | | must(down) | 6LR |
+----------------+-------------+-----+-----+--------------+----------+
Figure 22: Table that shows headers needed in Non-Storing mode: RPI,
RH3, IPv6-in-IPv6 encapsulation.
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8.1. Non-Storing Mode: Interaction between Leaf and Root
In this section is described the communication flow in Non Storing
Mode (Non-SM) between,
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/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 source to destination.
In this case, 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through from source (RAL) to destination
(6LBR).
This situation is the same case as storing mode.
The Figure 23 summarizes what headers are needed for this use case.
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+-----------+-----+-------+------+
| Header | RAL | 6LR_i | 6LBR |
| | src | | dst |
+-----------+-----+-------+------+
| Added | RPI | -- | -- |
| headers | | | |
+-----------+-----+-------+------+
| Modified | -- | RPI | -- |
| headers | | | |
+-----------+-----+-------+------+
| Removed | -- | -- | RPI |
| headers | | | |
+-----------+-----+-------+------+
| Untouched | -- | -- | -- |
| headers | | | |
+-----------+-----+-------+------+
Figure 23: 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 source to destination.
In this case, 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through from source (6LBR) to 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.
The Figure 24 summarizes what headers are needed for this use case.
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+-----------+----------+----------+----------+
| Header | 6LBR | 6LR_i | RAL |
| | src | | dst |
+-----------+----------+----------+----------+
| Added | RPI, RH3 | -- | -- |
| headers | | | |
+-----------+----------+----------+----------+
| Modified | -- | RPI, RH3 | -- |
| headers | | | |
+-----------+----------+----------+----------+
| Removed | -- | -- | RPI, RH3 |
| headers | | | |
+-----------+----------+----------+----------+
| Untouched | -- | -- | -- |
| headers | | | |
+-----------+----------+----------+----------+
Figure 24: 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 source to destination.
In this case, 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through from source (6LBR) to 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.
The Figure 25 depicts the table that summarizes what headers are
needed for this use case.
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+-----------+----------+--------------+----------------+----------+
| Header | 6LBR | 6LR_i | 6LR_n | RUL |
| | src | i=(1,..,n-1) | | dst |
| | | | | |
+-----------+----------+--------------+----------------+----------+
| Added | RPI, RH3 | -- | -- | -- |
| headers | | | | |
+-----------+----------+--------------+----------------+----------+
| Modified | -- | RPI, RH3 | RPI, | -- |
| headers | | | RH3(consumed) | |
+-----------+----------+--------------+----------------+----------+
| Removed | -- | -- | -- | -- |
| headers | | | | |
+-----------+----------+--------------+----------------+----------+
| Untouched | -- | -- | -- | RPI, RH3 |
| headers | | | | (both |
| | | | | ignored) |
+-----------+----------+--------------+----------------+----------+
Figure 25: 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 source to destination.
In this case, 1 <= i <= n, where n is the total number of routers
(6LR) that the packet goes through from source (RUL) to 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.
The Figure 26 shows the table that summarizes what headers are needed
for this use case.
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+---------+----+-----------------+-----------------+-----------------+
| |RUL | | | |
| Header |src | 6LR_1 | 6LR_i | 6LBR dst |
| |node| | | |
+---------+----+-----------------+-----------------+-----------------+
| Added | -- |IPv6-in-IPv6(RPI)| -- | -- |
| headers | | | | |
+---------+----+-----------------+-----------------+-----------------+
| Modified| -- | -- | RPI | -- |
| headers | | | | |
+---------+----+-----------------+-----------------+-----------------+
| Removed | -- | -- | -- |IPv6-in-IPv6(RPI)|
| headers | | | | |
+---------+----+-----------------+-----------------+-----------------+
|Untouched| -- | -- | -- | -- |
| headers | | | | |
+---------+----+-----------------+-----------------+-----------------+
Figure 26: Non-SM: Summary of the use of headers from RUL to root
8.2. Non-Storing Mode: Interaction between Leaf and Internet
This section will describe the communication flow in Non Storing Mode
(Non-SM) between:
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 source to destination,
1 <= i <= n, where n is the total number of routers (6LR) that the
packet goes through from source (RAL) to 6LBR.
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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
Figure 27 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].
The Figure 27 summarizes what headers are needed for this use case
when no encapsulation is used. The Figure 28 summarizes what headers
are needed for this use case when encapsulation to the root is used.
+-----------+-----+-------+------+-----------+
| Header | RAL | 6LR_i | 6LBR | Internet |
| | src | | | dst |
+-----------+-----+-------+------+-----------+
| Added | RPI | -- | -- | -- |
| headers | | | | |
+-----------+-----+-------+------+-----------+
| Modified | -- | RPI | RPI | -- |
| headers | | | | |
+-----------+-----+-------+------+-----------+
| Removed | -- | -- | -- | -- |
| headers | | | | |
+-----------+-----+-------+------+-----------+
| Untouched | -- | -- | -- | RPI |
| headers | | | | (Ignored) |
+-----------+-----+-------+------+-----------+
Figure 27: Non-SM: Summary of the use of headers from RAL to Internet
with no encapsulation
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+-----------+--------------+--------------+--------------+----------+
| Header | RAL | 6LR_i | 6LBR | Internet |
| | src | | | dst |
+-----------+--------------+--------------+--------------+----------+
| Added | IPv6-in-IPv6 | -- | -- | -- |
| headers | (RPI) | | | |
+-----------+--------------+--------------+--------------+----------+
| Modified | -- | | -- | -- |
| headers | | RPI | | |
+-----------+--------------+--------------+--------------+----------+
| Removed | -- | -- | IPv6-in-IPv6 | -- |
| headers | | | (RPI) | |
+-----------+--------------+--------------+--------------+----------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+-----------+--------------+--------------+--------------+----------+
Figure 28: 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,
1 <= i <= n, where n is the total number of routers (6LR) that the
packet goes through from 6LBR to 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].
The Figure 29 summarizes what headers are needed for this use case.
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+-----------+----------+--------------+--------------+--------------+
| Header | Internet | 6LBR | 6LR_i | RAL |
| | src | | | dst |
+-----------+----------+--------------+--------------+--------------+
| Added | -- | IPv6-in-IPv6 | -- | -- |
| headers | | (RH3, RPI) | | |
+-----------+----------+--------------+--------------+--------------+
| Modified | -- | -- | IPv6-in-IPv6 | -- |
| headers | | | (RH3, RPI) | |
+-----------+----------+--------------+--------------+--------------+
| Removed | -- | -- | -- | IPv6-in-IPv6 |
| headers | | | | (RH3, RPI) |
+-----------+----------+--------------+--------------+--------------+
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+-----------+----------+--------------+--------------+--------------+
Figure 29: 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 source to destination,
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).
The Figure 30 shows the table that summarizes what headers are needed
for this use case.
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+---------+----+-------------+--------------+--------------+--------+
| Header |RUL | 6LR_1 | 6LR_i | 6LBR |Internet|
| |src | | [i=2,..,n] | | dst |
| |node| | | | |
+---------+----+-------------+--------------+--------------+--------+
| Added | -- |IP6-IP6(RPI) | -- | -- | -- |
| headers | | | | | |
+---------+----+-------------+--------------+--------------+--------+
| Modified| -- | -- | RPI | -- | -- |
| headers | | | | | |
+---------+----+-------------+--------------+--------------+--------+
| Removed | -- | -- | -- | IP6-IP6(RPI) | -- |
| headers | | | | | |
+---------+----+-------------+--------------+--------------+--------+
|Untouched| -- | -- | -- | -- | -- |
| headers | | | | | |
+---------+----+-------------+--------------+--------------+--------+
Figure 30: 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 source to destination,
1 <= i <= n, where n is the total number of routers (6LR) that the
packet goes through from 6LBR to 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].
The Figure 31 shows the table that summarizes what headers are needed
for this use case.
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+----------+--------+------------------+-----------+-----------+-----+
| Header |Internet| 6LBR | 6LR_i | 6LR_n | RUL |
| | src | | | | dst |
+----------+--------+------------------+-----------+-----------+-----+
| Added | -- | IP6-IP6(RH3,RPI) | -- | -- | -- |
| headers | | | | | |
+----------+--------+------------------+-----------+-----------+-----+
| Modified | -- | -- | IP6-IP6 | -- | -- |
| headers | | | (RH3,RPI) | | |
+----------+--------+------------------+-----------+-----------+-----+
| Removed | -- | -- | -- | IP6-IP6 | -- |
| headers | | | | (RH3,RPI) | |
+----------+--------+------------------+-----------+-----------+-----+
|Untouched | -- | -- | -- | -- | -- |
| headers | | | | | |
+----------+--------+------------------+-----------+-----------+-----+
Figure 31: Non-SM: Summary of the use of headers from Internet to
RUL.
8.3. Non-SM: Interaction between leaves
In this section is described the communication flow in Non Storing
Mode (Non-SM) between,
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 source to the root, 1
<= ia <= n, where n is the total number of routers (6LR) that the
packet goes through from RAL to the root.
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6LR_id represents the intermediate routers from the root to the
destination, 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
upwards.
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
get ignored. The root inserts an RPI (RPI2) alongside the RH3.
Networks that use the RPL P2P extension [RFC6997] are essentially
non-storing DODAGs and fall into this scenario or scenario
Section 8.1.2, with the originating node acting as 6LBR.
The Figure 32 shows the table that summarizes what headers are needed
for this use case when encapsulation to the root takes place.
The Figure 33 shows the table that summarizes what 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.
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+---------+-------+----------+------------+----------+------------+
| Header | RAL | 6LR_ia | 6LBR | 6LR_id | RAL |
| | src | | | | dst |
+---------+-------+----------+------------+----------+------------+
| Added |IP6-IP6| | IP6-IP6 | -- | -- |
| headers |(RPI1) | -- |(RH3-> RAL, | | |
| | | | RPI2) | | |
+---------+-------+----------+------------+----------+------------+
| Modified| -- | | -- | IP6-IP6 | -- |
| headers | | RPI1 | |(RH3,RPI2)| |
+---------+-------+----------+------------+----------+------------+
| Removed | -- | -- | IP6-IP6 | -- | IP6-IP6 |
| headers | | | (RPI1) | | (RH3, |
| | | | | | RPI2) |
+---------+-------+----------+------------+----------+------------+
|Untouched| -- | -- | -- | -- | -- |
| headers | | | | | |
+---------+-------+----------+------------+----------+------------+
Figure 32: 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 |
+-----------+------+--------+---------+---------+---------+
| Inserted | 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)|
+-----------+------+--------+---------+---------+---------+
Figure 33: Non-SM: Summary of the Use of Headers from RAL to RAL
without encapsulation to the root.
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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 source to the root, 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, 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.
The Figure 34 shows the table that summarizes what headers are needed
for this use case when encapsulation to the root takes place. The
Figure 35 shows the table that summarizes what headers are needed for
this use case when no encapsulation to the root takes place.
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+-----------+---------+---------+---------+---------+---------+------+
| Header | RAL | 6LR_ia | 6LBR | 6LR_id | 6LR_m | RUL |
| | src | | | | | dst |
| | node | | | | | node |
+-----------+---------+---------+---------+---------+---------+------+
| Added | IP6-IP6 | | IP6-IP6 | -- | -- | -- |
| headers | (RPI1) | -- | (RH3, | | | |
| | | | RPI2) | | | |
+-----------+---------+---------+---------+---------+---------+------+
| Modified | -- | | -- | IP6-IP6 | | -- |
| headers | | RPI1 | | (RH3, | -- | |
| | | | | RPI2) | | |
+-----------+---------+---------+---------+---------+---------+------+
| Removed | -- | -- | IP6-IP6 | -- | IP6-IP6 | -- |
| headers | | | (RPI1) | | (RH3, | |
| | | | | | RPI2) | |
+-----------+---------+---------+---------+---------+---------+------+
| Untouched | -- | -- | -- | -- | -- | -- |
| headers | | | | | | |
+-----------+---------+---------+---------+---------+---------+------+
Figure 34: 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 |
| | src | | | | | dst |
| | node | | | | | node |
+-----------+------+--------+---------+---------+---------+---------+
| Inserted | 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)|
+-----------+------+--------+---------+---------+---------+---------+
Figure 35: Non-SM: Summary of the use of headers from RAL to RUL
without encapsulation to the root.
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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, 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, 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).
The Figure 36 shows the table that summarizes what headers are needed
for this use case.
+----------+------+---------+---------+---------+---------+---------+
| Header | RUL | 6LR_1 | 6LR_ia | 6LBR | 6LR_id | RAL |
| | src | | | | | dst |
| | node | | | | | node |
+----------+------+---------+---------+---------+---------+---------+
| Added | -- | IP6-IP6 | -- | IP6-IP6 | -- | -- |
| headers | | (RPI1) | | (RH3, | | |
| | | | | RPI2) | | |
+----------+------+---------+---------+---------+---------+---------+
| Modified | -- | | | -- | IP6-IP6 | -- |
| headers | | -- | RPI1 | | (RH3, | |
| | | | | | RPI2) | |
+----------+------+---------+---------+---------+---------+---------+
| Removed | -- | | -- | IP6-IP6 | -- | IP6-IP6 |
| headers | | -- | | (RPI1) | | (RH3, |
| | | | | | | RPI2) |
+----------+------+---------+---------+---------+---------+---------+
|Untouched | -- | -- | -- | -- | -- | -- |
| headers | | | | | | |
+----------+------+---------+---------+---------+---------+---------+
Figure 36: Non-SM: Summary of the use of headers from RUL to RAL.
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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 source to the root, 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, 1 <= id <= m, where m is the total number of the
intermediate routers (6LR).
This scenario is the combination of the previous two cases.
The Figure 37 shows the table that summarizes what headers are needed
for this use case.
+---------+------+-------+-------+---------+-------+---------+------+
| Header | RUL | 6LR_1 | 6LR_ia| 6LBR |6LR_id | 6LR_m | RUL |
| | src | | | | | | dst |
| | node | | | | | | node |
+---------+------+-------+-------+---------+-------+---------+------+
| Added | -- |IP6-IP6| -- | IP6-IP6 | -- | -- | -- |
| headers | | (RPI1)| | (RH3, | | | |
| | | | | RPI2) | | | |
+---------+------+-------+-------+---------+-------+---------+------+
| Modified| -- | -- | | -- |IP6-IP6| -- | -- |
| headers | | | RPI1 | | (RH3, | | |
| | | | | | RPI2)| | |
+---------+------+-------+-------+---------+-------+---------+------+
| Removed | -- | -- | -- | IP6-IP6 | -- | IP6-IP6 | -- |
| headers | | | | (RPI1) | | (RH3, | |
| | | | | | | RPI2) | |
+---------+------+-------+-------+---------+-------+---------+------+
|Untouched| -- | -- | -- | -- | -- | -- | -- |
| headers | | | | | | | |
+---------+------+-------+-------+---------+-------+---------+------+
Figure 37: Non-SM: Summary of the use of headers from RUL to RUL
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9. Operational Considerations of supporting RUL-leaves
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 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 are pre-RFC8200, or simply intolerant. Those nodes will
drop packets that continue to have RPL artifacts in them. In
general, such nodes can not 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 6, 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 only can 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-not-aware-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 storing mode can not know the final path of the traffic,
intolerant (that drop packets with RPL artifacts) leaf nodes can not
be supported.
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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 gets 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 to configure the current
network to the new value, through DIO messages and when all the nodes
are 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 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 to send
packets to not-RPL nodes. The not-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 [RFC6553] Destination
Options and Hop-by-Hop Options registry from 0x63 to 0x23 as shown in
Figure 38.
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+-------+-------------------+------------------------+---------- -+
| Hex | Binary Value | Description | Reference |
+ Value +-------------------+ + +
| | act | chg | rest | | |
+-------+-----+-----+-------+------------------------+------------+
| 0x23 | 00 | 1 | 00011 | RPL Option |[RFCXXXX](*)|
+-------+-----+-----+-------+------------------------+------------+
| 0x63 | 01 | 1 | 00011 | RPL Option(DEPRECATED) | [RFC6553] |
| | | | | |[RFCXXXX](*)|
+-------+-----+-----+-------+------------------------+------------+
Figure 38: Option Type in RPL Option.(*)represents this document
DODAG Configuration option is updated as follows (Figure 39):
+------------+-----------------+---------------+
| Bit number | Description | Reference |
+------------+-----------------+---------------+
| 3 | RPI 0x23 enable | This document |
+------------+-----------------+---------------+
Figure 39: DODAG Configuration option Flag to indicate the RPI-flag-
day.
11.2. Change to the DODAG Configuration Options Flags registry
This document requests IANA to change the name of the "DODAG
Configuration Option Flags" registry to "DODAG Configuration Option
Flags for MOP 0..6".
This document requests to be mentioned as a reference for this
change.
11.3. Change MOP value 7 to Reserved
This document requests the changing the registration status of value
7 in the Mode of Operation registry from Unassigned to Reserved.
This change is in support of future work.
This document requests to be mentioned as a reference for this entry
in the registry.
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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 [I-D.ietf-anima-autonomic-control-plane], which may be
equipped with multiple 100Gb/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
BCP38 [BCP38] filtering at the RPL root on egress traffic will both
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, BCP38 filtering
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 [I-D.ietf-anima-bootstrapping-keyinfra]
and [I-D.ietf-6tisch-dtsecurity-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 using forged source
addresses. If the attack requires bi-directional 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
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section of [RFC2473], 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] goes
into some detail on what additional details would be needed in order
to "Use IPsec". Use of ESP would prevent [RFC8138] compression
(compression must occur before encryption), and [RFC8138] compression
is lossy in a way that prevents use of AH. These are minor issues.
The major issue is how to establish trust enough such that 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 resource 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 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 RFC 2473. IPsec is not
recommended.
An LLN with hostile nodes within it would not be protected against
impersonation with 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. As 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
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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 and 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 it's final destination.
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. This is done in order to avoid:
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 in 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 on non-obvious ways, perhaps eluding observation.
This usage appears consistent with a normal operation of [RFC6997]
and can not 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 Distributed Denial Of Service 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
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[I-D.ietf-6lo-ap-nd]. 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 an
L2 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 RFC6554, section 3).
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 [BCP38] processing
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
[I-D.ietf-6lo-backbone-router]. In this case the BCP38 filtering
needs to take this into account, either by exchanging detailed
routing information on each LLN, or by moving the BCP38 filtering
further towards the Internet, so that the details of the multiple
LLNs do not matter.
13. 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 the
Section 4. Much of the redaction in that section is based on his
comments.
Additionally, the authors would like to acknowledge the review,
feedback, and comments of (alphabetical order): Dominique Barthel,
Robert Cragie, Simon Duquennoy, Ralph Droms, Cenk Guendogan, Rahul
Jadhav, Benjamin Kaduk, Matthias Kovatsch, Gustavo Mercado,
Subramanian Moonesamy, Marcela Orbiscay, Charlie Perkins, Cristian
Perez, Alvaro Retana, Peter van der Stok, Xavier Vilajosana, Eric
Vyncke and Thomas Watteyne.
14. References
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14.1. 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, DOI 10.17487/RFC2827,
May 2000, <https://www.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>.
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[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>.
14.2. Informative References
[DDOS-KREBS]
Goodin, D., "Record-breaking DDoS reportedly delivered by
>145k hacked cameras", September 2016,
<http://arstechnica.com/security/2016/09/botnet-of-145k-
cameras-reportedly-deliver-internets-biggest-ddos-ever/>.
[I-D.ietf-6lo-ap-nd]
Thubert, P., Sarikaya, B., Sethi, M., and R. Struik,
"Address Protected Neighbor Discovery for Low-power and
Lossy Networks", draft-ietf-6lo-ap-nd-23 (work in
progress), April 2020.
[I-D.ietf-6lo-backbone-router]
Thubert, P., Perkins, C., and E. Levy-Abegnoli, "IPv6
Backbone Router", draft-ietf-6lo-backbone-router-20 (work
in progress), March 2020.
[I-D.ietf-6tisch-dtsecurity-zerotouch-join]
Richardson, M., "6tisch Zero-Touch Secure Join protocol",
draft-ietf-6tisch-dtsecurity-zerotouch-join-04 (work in
progress), July 2019.
[I-D.ietf-anima-autonomic-control-plane]
Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
Control Plane (ACP)", draft-ietf-anima-autonomic-control-
plane-30 (work in progress), October 2020.
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[I-D.ietf-anima-bootstrapping-keyinfra]
Pritikin, M., Richardson, M., Eckert, T., Behringer, M.,
and K. Watsen, "Bootstrapping Remote Secure Key
Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping-
keyinfra-45 (work in progress), November 2020.
[I-D.ietf-intarea-tunnels]
Touch, J. and M. Townsley, "IP Tunnels in the Internet
Architecture", draft-ietf-intarea-tunnels-10 (work in
progress), September 2019.
[I-D.ietf-roll-unaware-leaves]
Thubert, P. and M. Richardson, "Routing for RPL Leaves",
draft-ietf-roll-unaware-leaves-29 (work in progress),
January 2021.
[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>.
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[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>.
Authors' Addresses
Maria Ines Robles
Universidad Tecno. Nac.(UTN)-FRM, Argentina/ Aalto University Finland
Email: mariainesrobles@gmail.com
Michael C. Richardson
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z 5V7
CA
Email: mcr+ietf@sandelman.ca
URI: http://www.sandelman.ca/mcr/
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Pascal Thubert
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
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