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draft-ietf-roll-useofrplinfo.xml
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draft-ietf-roll-useofrplinfo.xml
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<?xml version="1.0"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!ENTITY RFC6550 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6550.xml">
<!ENTITY RFC8138 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.8138.xml">
<!ENTITY RFC8200 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.8200.xml">
<!ENTITY RFC6553 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6553.xml">
<!ENTITY RFC6554 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6554.xml">
<!ENTITY RFC2119 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">
<!ENTITY RFC7102 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.7102.xml">
<!ENTITY RFC4443 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4443.xml">
<!ENTITY RFC6775 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6775.xml">
<!ENTITY RFC2473 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.2473.xml">
<!ENTITY RFC4302 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4302.xml">
<!ENTITY RFC4301 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4301.xml">
<!ENTITY RFC4303 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4303.xml">
<!ENTITY RFC7321 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.7321.xml">
<!ENTITY RFC7416 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.7416.xml">
<!ENTITY RFC4192 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.4192.xml">
<!--<!ENTITY I-D.thubert-roll-unaware-leaves SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.I-D.thubert-roll-unaware-leaves.xml"> -->
<!--<!ENTITY I-D.ietf-6tisch-architecture SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-6tisch-architecture.xml">-->
<!ENTITY I-D.moore-iot-security-bcp SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.moore-iot-security-bcp.xml">
<!--<!ENTITY I-D.ietf-roll-dao-projection SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-roll-dao-projection.xml">-->
]>
<!--<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?> -->
<!-- used by XSLT processors -->
<!-- For a complete list and description of processing instructions (PIs),
please see http://xml.resource.org/authoring/README.html. -->
<!-- Below are generally applicable Processing Instructions (PIs) that most I-Ds might want to use.
(Here they are set differently than their defaults in xml2rfc v1.32) -->
<?rfc strict="no" ?>
<!-- give errors regarding ID-nits and DTD validation -->
<!-- control the table of contents (ToC) -->
<?rfc toc="yes"?>
<!-- generate a ToC -->
<?rfc tocdepth="4"?>
<!-- the number of levels of subsections in ToC. default: 3 -->
<!-- control references -->
<?rfc symrefs="yes"?>
<!-- use symbolic references tags, i.e, [RFC2119] instead of [1] -->
<?rfc sortrefs="yes" ?>
<!-- sort the reference entries alphabetically -->
<!-- control vertical white space
(using these PIs as follows is recommended by the RFC Editor) -->
<?rfc compact="yes" ?>
<!-- do not start each main section on a new page -->
<?rfc subcompact="no" ?>
<!-- keep one blank line between list items -->
<!-- end of list of popular I-D processing instructions -->
<rfc category="std" docName="draft-ietf-roll-useofrplinfo-latest" ipr="trust200902" updates="6553, 6550, 8138">
<!-- category values: std, bcp, info, exp, and historic
ipr values: trust200902, noModificationTrust200902, noDerivativesTrust200902,
or pre5378Trust200902
you can add the attributes updates="NNNN" and obsoletes="NNNN"
they will automatically be output with "(if approved)" -->
<!-- ***** FRONT MATTER ***** -->
<front>
<!-- The abbreviated title is used in the page header - it is only necessary if the
full title is longer than 39 characters -->
<title abbrev="Useof6553">When to use RFC 6553, 6554 and IPv6-in-IPv6</title>
<author initials="M.I." surname="Robles" fullname="Maria Ines Robles">
<organization abbrev="AaltoU">Aalto University </organization>
<address>
<postal>
<street>Innopoli</street>
<city>Espoo</city>
<code>02150</code>
<country>Finland</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author initials="M." surname="Richardson" fullname="Michael C. Richardson">
<organization abbrev="SSW">Sandelman Software Works</organization>
<address>
<postal>
<street>470 Dawson Avenue</street>
<city>Ottawa</city>
<region>ON</region>
<code>K1Z 5V7</code>
<country>CA</country>
</postal>
<email>[email protected]</email>
<uri>http://www.sandelman.ca/mcr/</uri>
</address>
</author>
<author initials="P." surname="Thubert" fullname="Pascal Thubert">
<organization abbrev="Cisco">Cisco Systems, Inc</organization>
<address>
<postal>
<street> Village d'Entreprises Green Side 400, Avenue de Roumanille</street>
<city>Batiment T3</city>
<region>Biot - Sophia Antipolis </region>
<code>06410</code>
<country>France</country>
</postal>
<email>[email protected] </email>
<uri></uri>
</address>
</author>
<date year="2018" />
<area>Internet</area>
<workgroup>ROLL Working Group</workgroup>
<keyword>RPL Option</keyword>
<keyword>6LoWPAN</keyword>
<keyword>RFC 6553</keyword>
<abstract>
<t>
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 RFC 6553, RFC 6554 and IPv6-in-IPv6 encapsulation is required.
This analysis provides the basis on which to design efficient compression of these headers.
This document updates RFC 6553 adding a change to the RPL Option Type. Additionally, this document updates
RFC 6550 to indicate about this change and updates RFC8138 as well to consider the new Option Type
when RPL Option is decompressed.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
<xref target="RFC6550"/> is a routing protocol for
constrained networks. RFC 6553 <xref target="RFC6553"/>
defines the "RPL option" (RPI), carried within the IPv6 Hop-by-Hop
header to quickly identify
inconsistencies (loops) in the routing topology. RFC 6554 <xref
target="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.
</t>
<t>
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 traffic at all which is mostly hop-by-hop
traffic (one exception being DAO messages in non-storing mode).
</t>
<t>
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 implementors
agree when artifacts are necessary, or when they can be safely
omitted, or removed.
</t>
<t>
An interim meeting went through the 24 cases defined here to
discover if there were any shortcuts, and this document is the
result of that discussion. This document clarifies what is the correct and
the incorrect behaviour.
</t>
<t>
The related document <xref target="RFC8138"> A Routing Header
Dispatch for 6LoWPAN (6LoRH) </xref> defines a method to
compress RPL Option information and Routing Header type 3
<xref
target="RFC6554"/>, an efficient IP-in-IP technique, and use cases
proposed for the <xref target="Second6TischPlugtest"/>
involving 6loRH.
</t>
</section>
<section title="Terminology and Requirements Language">
<t>
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described
in <xref target="RFC2119">RFC 2119</xref>.
</t>
<t>
Terminology defined in <xref target="RFC7102"/> applies to this document: LBR, LLN, RPL, RPL Domain and ROLL.
</t>
<t>
RPL-node: A device which implements RPL, thus we can say that the device is RPL-capable or RPL-aware.
Please note that the device can be found inside the LLN or outside LLN.
In this document a RPL-node which is a leaf of a DODAG is called RPL-aware-leaf.
</t>
<t>
RPL-not-capable: A device which does not implement RPL, thus we can say that the device is not-RPL-aware.
Please note that the device can be found inside the LLN.
In this document a not-RPL-aware node which is a leaf of a DODAG is
called not-RPL-aware-leaf.
</t>
<t>
pledge: a new device which seeks admission to a network. (from <xref target="I-D.ietf-anima-bootstrapping-keyinfra" />)
</t>
<t>
Join Registrar and Coordinator (JRC): a device which brings new nodes
(pledges) into a network. (from <xref target="I-D.ietf-anima-bootstrapping-keyinfra" />)
</t>
<t>
Flag day: A "flag day" is a procedure in which the network, or a part of it, is
changed during a planned outage, or suddenly, causing an outage while
the network recovers <xref target="RFC4192"/>
</t>
<section title="hop-by-hop IPv6-in-IPv6 headers">
<t>
The term "hop-by-hop IPv6-in-IPv6" header refers to: adding a header
that originates from a node to an adjacent node, using the
addresses (usually the GUA or ULA, but could use the link-local addresses)
of each node. If the packet must traverse multiple hops, then it
must be decapsulated at each hop, and then re-encapsulated again
in a similar fashion.
</t>
</section>
</section>
<section anchor="updateRFCs_section" title="Updates to RFC6553, RFC6550 and RFC 8138">
<section title="Updates to RFC 6553">
<t>
This modification is required to be able to send, for example,
IPv6 packets from a RPL-aware-leaf to a not-RPL-aware node through Internet (see <xref target="sm-Ral2i" />),
without requiring IP-in-IP encapsulation.
</t>
<t>
<xref target="RFC6553"/> states as showed below, that in the Option Type field of the RPL Option
header, 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 en route.
The remaining bits serve as the option type.
</t>
<t>
<figure title="Option Type in RPL Option." anchor="fig_RPIOption" align="center">
<artwork> <![CDATA[
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
0x63 01 1 00011 RPL Option [RFC6553]
]]></artwork></figure>
</t>
<t>
Recent changes in
<xref target="RFC8200"/> (section 4, page 8), states: "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". Processing of the Hop-by-Hop Options header (by IPv6 intermediate nodes) is now optional,
but if they are configured to process the header,
and if such nodes encounter an option with the first two bits set to 01,
they will drop the packet (if they conform to <xref target="RFC8200"/>).
Host systems should do the same, irrespective of the configuration.
</t>
<t>
Based on That, if an IPv6 (intermediate) node (RPL-not-capable) receives a packet with an
RPL Option, it should ignore the HBH RPL option
(skip over this option and continue processing the header). This is relevant, as we mentioned previously, in the case that
we have a flow from RPL-aware-leaf to Internet (see <xref target="sm-Ral2i" />).
</t>
<t>
Thus, this document updates the Option Type field to:
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
(<xref target="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 remaining bits serve as the option type and remain as 0x3.
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
[RFC6553] RPL Hop-by-Hop option known as RPI.
</t>
<t>
This is a significant update to <xref target="RFC6553"/>. [RFCXXXX] represents this document.
</t>
<t>
<figure title="Revised Option Type in RPL Option." anchor="fig_RPIOption_new" align="center">
<artwork> <![CDATA[
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
0x23 00 1 00011 RPL Option [RFCXXXX]
]]></artwork></figure>
</t>
<t>
This change creates a flag day for existing networks which are
currently using 0x63 as the RPI value. A move to 0x23 will not
be understood by those networks. It is suggested that
implementations accept both 0x63 and 0x23 when
processing.
</t>
<t>
When forwarding packets, implementations SHOULD use
the same value as it was received (This is required because,
RPI type code can not be changed by <xref target="RFC8200"/>).
It allows to the network to be incrementally upgraded,
and for the DODAG root to know which parts of the network are upgraded.
</t>
<t>
When originating new packets,
implementations SHOULD have an option to determine which value to
originate with, this option is controlled by the DIO option
described below.
</t>
<t>
A network which is switching from straight 6lowpan compression
mechanism to those described in
<xref target="RFC8138" />
will experience a flag day in the data compression anyway, and if
possible this change can be deployed at the same time.
</t>
<!-- <t>
In general, any packet that leaves the RPL domain
of an LLN (or leaves the LLN entirely) will NOT be discarded, when it has the <xref target="RFC6553" /> RPL Option
Header known as the RPI or <xref target="RFC6554" /> SRH3 Extension Header (S)RH3.
Because of <xref target="RFC8200"/> the RPI Hop-by-Hop option
MAY be left in place even if the end host does not
understand it.
</t>
-->
</section>
<section title="Updates to RFC 8138">
<t>
RPI-6LoRH header provides a compressed form for the RPL RPI <xref target="RFC8138"/>.
It should be considered when the Option Type in RPL Option is decompressed,
should take the value of 0x23 instead of 0x63.
</t>
</section>
<section title="Updates to RFC 6550: Indicating the new RPI in the DODAG Configuration Option Flag. ">
<t>
In order to avoid a flag day caused by lack of interoperation
between new RPI (0x23) and old RPI (0x63) nodes, when there is a
mix of new nodes and old nodes, the new nodes may be put into a
compatibility mode until all of the old nodes are replaced or
upgraded.
</t>
<t>
This can be done via a DODAG Configuration Option flag which will propogate
through the network. Failure to receive this information will cause new
nodes to remain in compatibility mode, and originate traffic with
the old-RPI (0x63) value.
</t>
<t>
As stated in <xref target="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.
</t>
<t>
The DODAG Configuration Option has a Flags field which is modified by this document.
Currently, the DODAG Configuration Option in <xref target="RFC6550"/> is as follows. .
</t>
<t>
Flags: The 4-bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender
and MUST be ignored by the receiver.
</t>
<t>
<figure title="DODAG Configuration Option." anchor="fig_ConfOption" align="center">
<artwork> <![CDATA[
0 1 2 3
+-----------------+---------------------------------------------------+
| Type = 0x04 | Opt Length = 14| Flags | A | PCS| DIOIntDoubl. |
+---------------------------------------------------------------------+
| DIOIntMin. | DIORedund. | MaxRankIncrease |
+-----------------+---------------------------------------------------+
| MinHopRankIncrease | OCP |
+-----------------+---------------------------------------------------+
|Reserved | Def. Lifetime | Lifetime Unit |
+-----------------+-----------------+---------------------------------+
]]></artwork></figure>
</t>
<t>
Bit number three of flag field in the DODAG Configuration option
is to be used as follows:
</t>
<t>
<figure title="DODAG Configuration Option Flag to indicate the RPI-flag-day." anchor="fig_RPIflagday2" align="center">
<artwork> <![CDATA[
+------------+-----------------+---------------+
| Bit number | Description | Reference |
+------------+-----------------+---------------+
| 3 | RPI 0x23 enable | This document |
+------------+-----------------+---------------+
]]></artwork></figure>
</t>
<t>
In case of rebooting, the node does not remember the flag. Thus,
the DIO is sent with flag indicating the new RPI value.
</t>
</section>
</section>
<section title="Sample/reference topology">
<t>
A RPL network in general is composed of a 6LBR (6LoWPAN Border Router),
Backbone Router (6BBR), 6LR (6LoWPAN Router) and 6LN (6LoWPAN
Node) as leaf logically organized in a DODAG structure.
(Destination Oriented Directed Acyclic Graph).
</t>
<t>
RPL defines the RPL Control messages (control plane), a new
ICMPv6 <xref target="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 showed in Figure 5.
</t>
<t>
RPL supports two modes of Downward traffic: in storing mode (RPL-SM),
it is fully stateful; in non-storing (RPL-NSM), 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
storing and non-storing nodes is not supported with the
current specifications at the time of writing this document.
</t>
<t>
<figure title="RPL Stack." anchor="fig_RPLStack" align="center">
<artwork><![CDATA[
+--------------+
| Upper Layers |
| |
+--------------+
| RPL |
| |
+--------------+
| ICMPv6 |
| |
+--------------+
| IPv6 |
| |
+--------------+
| 6LoWPAN |
| |
+--------------+
| PHY-MAC |
| |
+--------------+
]]></artwork></figure>
</t>
<t>
<figure title="A reference RPL Topology." anchor="fig_CommonTopology" align="center">
<artwork><![CDATA[
+------------+
| INTERNET ----------+
| | |
+------------+ |
|
|
|
A |
+-------+
|6LBR |
+-----------|(root) |-------+
| +-------+ |
| |
| |
| |
| |
| B |C
+---|---+ +---|---+
| 6LR | | 6LR |
+-------->| |--+ +--- ---+
| +-------+ | | +-------+ |
| | | |
| | | |
| | | |
| | | |
| D | E | |
+-|-----+ +---|---+ | |
| 6LR | | 6LR | | |
| | +------ | | |
+---|---+ | +---|---+ | |
| | | | |
| | +--+ | |
| | | | |
| | | | |
| | | I | J |
F | | G | H | |
+-----+-+ +-|-----+ +---|--+ +---|---+ +---|---+
| Raf | | ~Raf | | Raf | | Raf | | ~Raf |
| 6LN | | 6LN | | 6LN | | 6LN | | 6LN |
+-------+ +-------+ +------+ +-------+ +-------+
]]>
</artwork></figure>
</t>
<t>
Figure 2 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.
</t>
<t>
But, the 6LN leaves (Raf - "RPL aware leaf"-)
marked as (F, H and I) are RPL nodes with no children hosts.
</t>
<t>
The leafs marked as ~Raf "not-RPL aware leaf" (G and J) are
devices which do not speak RPL at all (not-RPL-aware),
but uses Router-Advertisements, 6LowPAN DAR/DAC and
efficient-ND only to participate in the network <xref target="RFC6775"/>.
In the document these leafs (G and J) are also refered to as
an IPv6 node.
</t>
<t>
The 6LBR ("A") in the figure is the root of the Global DODAG.
</t>
</section>
<section title="Use cases">
<t>
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.
</t>
<t>
This document assumes that the LLN is using the no-drop RPI option (0x23).
</t>
<t>
The uses cases describe the communication between RPL-aware-nodes,
with the root (6LBR), and with Internet.
This document also describe the communication between nodes
acting as leaves that do not understand RPL, but are part of the LLN.
We name these nodes as not-RPL-aware-leaf.
(e.g. <xref target="sm-nRal2root" /> Flow from not-RPL-aware-leaf to root)
We describe also how is the communication inside of the LLN
when it has the final destination addressed outside of the LLN e.g. with
destination to Internet.
(e.g. <xref target="sm-nRal2i" /> Flow from not-RPL-aware-leaf to Internet)
</t>
<t>
The uses cases comprise as follow:
</t>
<t>
Interaction between Leaf and Root:
</t>
<t>
<list>
<t>
RPL-aware-leaf to root
</t>
<t>
root to RPL-aware-leaf
</t>
<t>
not-RPL-aware-leaf to root
</t>
<t>
root to not-RPL-aware-leaf
</t>
</list>
</t>
<t>
Interaction between Leaf and Internet:
</t>
<t>
<list>
<t>
RPL-aware-leaf to Internet
</t>
<t>
Internet to RPL-aware-leaf
</t>
<t>
not-RPL-aware-leaf to Internet
</t>
<t>
Internet to not-RPL-aware-leaf
</t>
</list>
</t>
<t>
Interaction between Leafs:
</t>
<t>
<list>
<t>
RPL-aware-leaf to RPL-aware-leaf (storing and non-storing)
</t>
<t>
RPL-aware-leaf to not-RPL-aware-leaf (non-storing)
</t>
<t>
not-RPL-aware-leaf to RPL-aware-leaf (storing and non-storing)
</t>
<t>
not-RPL-aware-leaf to not-RPL-aware-leaf (non-storing)
</t>
</list>
</t>
<t>
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 <xref target="RFC8200" />. Extensions may not
be added or removed except by the sender or the receiver.
</t>
<t>
However, unlike <xref target="RFC6553" />, the Hop-by-Hop Option
Header used for the RPI artifact has the first two bits set to
'00'.
This means that the RPI artifact will be ignored when received by a host
or router that does not understand that option
( Section 4.2 <xref target="RFC8200" />).
</t>
<t>
This means that when the no-drop RPI option code 0x23 is used, a
packet that leaves the RPL domain of an LLN (or that leaves the LLN
entirely) will not be discarded when it contains the [RFC6553] RPL
Hop-by-Hop option known as RPI. Thus, the RPI Hop-by-Hop option MAY
be left in place even if the end host does not understand it.
</t>
<t>
NOTE: There is some possible security risk when the RPI
information is released to the Internet. At this point this is
a theoretical situation; no clear attack has been described.
At worst, it is clear that the RPI option would waste some
network bandwidth when it escapes. This is traded off against
the savings in the LLN by not having to encapsulate the packet in
order to remove the artifact.
</t>
<t>
Despite being legal to leave the RPI artifact in place,
an intermediate router that needs to add an extension header
(SHR3 or RPI Option) MUST still encapsulate the packet in an
(additional) outer IP header. The new header is placed after
this new outer IP header.
</t>
<t>
A corollory is that an SHR3 or RPI 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.
When it does so, 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 addresses.
</t>
<t>
Both RPI and RH3 headers may be modified in very specific ways
by routers on the path of the packet without the need to add to
remove an encapsulating header. Both headers were designed with
this modification in
mind, and both the RPL RH 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.
</t>
<t>
RPI should be present in every single RPL data packet. There is one
exception in non-storing mode: when a packet is going down from the
root. In a downward non-storing mode, the entire route is
written, so there can be no loops by construction, nor any
confusion about which forwarding table to use (as the root has
already made all routing decisions). However, there are still
cases, such as in 6tisch, where the instanceID portion of the RPI
header may still be needed to pick an appropriate priority or
channel at each hop.
</t>
<t>
In the tables present in this document, the term "RPL aware leaf"
is has been shortened to
"Raf", and "not-RPL aware leaf" has been shortened to "~Raf" to
make the table fit in available space.
</t>
<t>
The earlier examples are more extensive to make sure that the
process is clear, while later examples are more concise.
</t>
</section>
<section title="Storing mode">
<t>
In storing mode (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 PIO option.
</t>
<t>
The following table itemizes which headers are needed in the following
scenarios, and indicates if the IP-in-IP header must be
inserted on a hop-by-hop basis, or when it can target the
destination node directly. There are these possible situations:
hop-by-hop necessary (indicated by "hop"), or destination address
possible (indicated by "dst"). In all cases hop by hop MAY be
used.
</t>
<t>
In cases where no IP-in-IP header is needed, the column is left
blank.
</t>
<t>
In all cases the RPI headers are needed, since it identifies
inconsistencies (loops) in the routing topology.
In all cases the RH3 is not needed because we do not
indicate the route in storing mode.
</t>
<t>
In each case, 6LR_i are the intermediate routers from source to destination.
"1 <= i >= n", n is the number of routers (6LR)
that the packet go through from source (6LN) to destination.
</t>
<t>
The leaf can be a router 6LR or a host, both indicated as 6LN
(see <xref target="fig_CommonTopology" />).
</t>
<t>
<!-- Figure saved with the name IP-in-IP_encapsulation_in_Storing_mode.tgn -->
<!-- to edit table, access to http://www.tablesgenerator.com/ and load the table -->
<figure title="IP-in-IP encapsulation in Storing mode." anchor="fig_EncStoMode" align="center">
<artwork><![CDATA[
+---------------------+--------------+----------+--------------+
| Interaction between | Use Case | IP-in-IP | IP-in-IP dst |
+---------------------+--------------+----------+--------------+
| | Raf to root | No | -- |
+ +--------------+----------+--------------+
| Leaf - Root | root to Raf | No | -- |
+ +--------------+----------+--------------+
| | root to ~Raf | No | -- |
+ +--------------+----------+--------------+
| | ~Raf to root | Yes | root |
+---------------------+--------------+----------+--------------+
| | Raf to Int | No | -- |
+ +--------------+----------+--------------+
| Leaf - Internet | Int to Raf | Yes | Raf |
+ +--------------+----------+--------------+
| | ~Raf to Int | Yes | root |
+ +--------------+----------+--------------+
| | Int to ~Raf | Yes | hop |
+---------------------+--------------+----------+--------------+
| | Raf to Raf | No | -- |
+ +--------------+----------+--------------+
| | Raf to ~Raf | No | -- |
+ Leaf - Leaf +--------------+----------+--------------+
| | ~Raf to Raf | Yes | dst |
+ +--------------+----------+--------------+
| | ~Raf to ~Raf | Yes | hop |
+---------------------+--------------+----------+--------------+
]]></artwork></figure>
</t>
<section title="Storing Mode: Interaction between Leaf and Root">
<t>
In this section we are going to describe the communication flow
in storing mode (SM) between,
</t>
<t>
<list>
<t>
RPL-aware-leaf to root
</t>
<t>
root to RPL-aware-leaf
</t>
<t>
not-RPL-aware-leaf to root
</t>
<t>
root to not-RPL-aware-leaf
</t>
</list>
</t>
<!-- 5.1. Example of Flow from RPL-aware-leaf to root !-->
<section title="SM: Example of Flow from RPL-aware-leaf to root">
<t>
In storing mode, RFC 6553 (RPI) is used
to send RPL Information instanceID and rank
information.
</t>
<t>
As stated in Section 16.2 of <xref
target="RFC6550"/> an RPL-aware-leaf node does not
generally issue DIO messages; a leaf node accepts
DIO messages from upstream.
(When the inconsistency in routing occurs, a leaf
node will generate a DIO with an infinite rank, to
fix it). It may issue DAO and DIS
messages though it generally ignores DAO and DIS
messages.
</t>
<t>
In this case the flow comprises:
</t>
<t>
RPL-aware-leaf (6LN) --> 6LR_i --> root(6LBR)
</t>
<t>
For example, a communication flow could be: Node F --> Node E --> Node B --> Node A root(6LBR)
</t>
<t>
As it was mentioned in this document 6LRs, 6LBR are always
full-fledged RPL routers.
</t>
<t>
The 6LN (Node F) inserts the RPI header, and sends the
packet to 6LR (Node E) which decrements the rank in RPI and
sends the packet up. When the packet arrives at
6LBR (Node A), the RPI is removed and the packet is
processed.
</t>
<t>
No IP-in-IP header is required.
</t>
<t> The RPI header can be removed by the 6LBR
because the packet is addressed to the 6LBR. The
6LN must know that it is communicating with the 6LBR
to make use of this scenario.
The 6LN can know the address of the 6LBR because it
knows the address of the root via the DODAGID in the
DIO messages.
</t>
<texttable title="Storing: Summary of the use of headers from RPL-aware-leaf to root">
<ttcol> Header</ttcol>
<ttcol> 6LN</ttcol>
<ttcol> 6LR_i</ttcol>
<ttcol> 6LBR</ttcol>
<c> Inserted headers</c>
<c> RPI</c>
<c> -- </c>
<c> -- </c>
<c> Removed headers</c>
<c> -- </c>
<c> -- </c>
<c> RPI </c>
<c> Re-added headers</c>
<c> -- </c>
<c> -- </c>
<c> -- </c>
<c> Modified headers</c>
<c> -- </c>
<c> RPI </c>
<c> -- </c>
<c> Untouched headers</c>
<c> -- </c>
<c> --</c>
<c> --</c>
</texttable>
</section>
<!-- section 6.2. !-->
<section title="SM: Example of Flow from root to RPL-aware-leaf">
<t>
In this case the flow comprises:
</t>
<t>
root (6LBR) --> 6LR_i --> RPL-aware-leaf (6LN)
</t>
<t>
For example, a communication flow could be: Node A root(6LBR) --> Node B --> Node D --> Node F
</t>
<t>
In this case the 6LBR inserts RPI header and
sends the packet down, the 6LR is going to
increment the rank in RPI (it examines the
instanceID to identify the right forwarding
table),
the packet
is processed in the 6LN and the RPI removed.
</t>
<t>
No IP-in-IP header is required.
</t>
<texttable title="Storing: Summary of the use of headers from root to RPL-aware-leaf">
<ttcol> Header</ttcol>
<ttcol> 6LBR</ttcol>
<ttcol> 6LR_i</ttcol>
<ttcol> 6LN</ttcol>
<c> Inserted headers</c>
<c> RPI </c>
<c> -- </c>
<c> -- </c>
<c> Removed headers</c>
<c> -- </c>
<c> -- </c>
<c> RPI </c>
<c> Re-added headers</c>
<c> -- </c>
<c> -- </c>
<c> -- </c>
<c> Modified headers</c>
<c> -- </c>
<c> RPI </c>
<c> -- </c>
<c> Untouched headers</c>
<c> -- </c>
<c> -- </c>
<c> -- </c>
</texttable>
</section>
<!-- section 6.3. !-->
<section title="SM: Example of Flow from root to not-RPL-aware-leaf">
<t>
In this case the flow comprises:
</t>
<t>
root (6LBR) --> 6LR_i --> not-RPL-aware-leaf (IPv6)
</t>
<t>
For example, a communication flow could be: Node A root(6LBR) --> Node B --> Node E --> Node G
</t>
<t>
As the RPI extension can be ignored by the
not-RPL-aware leaf, this situation is identical to
the previous scenario.
</t>
<texttable title="Storing: Summary of the use of headers from root to not-RPL-aware-leaf">
<ttcol> Header</ttcol>
<ttcol> 6LBR</ttcol>
<ttcol> 6LR_i</ttcol>
<ttcol> IPv6</ttcol>
<c> Inserted headers</c>
<c> RPI </c>
<c> -- </c>
<c> -- </c>
<c> Removed headers</c>
<c> -- </c>
<c> -- </c>
<c> -- </c>
<c> Re-added headers</c>
<c> -- </c>
<c> -- </c>
<c> -- </c>
<c> Modified headers</c>
<c> -- </c>
<c> RPI </c>
<c> -- </c>
<c> Untouched headers</c>
<c> -- </c>
<c> -- </c>
<c> RPI (Ignored) </c>
</texttable>
</section>
<section anchor="sm-nRal2root" title="SM: Example of Flow from not-RPL-aware-leaf to root">
<t>
In this case the flow comprises:
</t>
<t>
not-RPL-aware-leaf (IPv6) --> 6LR_1 --> 6LR_i --> root (6LBR)
</t>
<t>
For example, a communication flow could be: Node G --> Node E --> Node B --> Node A root(6LBR)
</t>
<t>
When the packet arrives from IPv6 node (Node G) to
6LR_1 (Node E), the 6LR_1 will insert a RPI header, encapsuladed
in a IPv6-in-IPv6 header. The IPv6-in-IPv6
header can be addressed to the next hop (Node B), or to
the root (Node A). The root removes the header and processes
the packet.
</t>
<texttable title="Storing: Summary of the use of headers from not-RPL-aware-leaf to root">
<ttcol> Header</ttcol>
<ttcol> IPv6</ttcol>
<ttcol> 6LR_1</ttcol>
<ttcol> 6LR_i</ttcol>