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draft-ietf-roll-capabilities.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<!-- This template is for creating an Internet Draft using xml2rfc,
which is available here: http://xml.resource.org. -->
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
<!-- One method to get references from the online citation libraries.
There has to be one entity for each item to be referenced.
An alternate method (rfc include) is described in the references. -->
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<!ENTITY RFC3552 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.3552.xml">
<!ENTITY RFC6550 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6550.xml">
<!ENTITY RFC6551 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6551.xml">
<!ENTITY RFC6345 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.6345.xml">
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<!ENTITY RFC5191 SYSTEM "http://xml.resource.org/public/rfc/bibxml/reference.RFC.5191.xml">
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]>
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
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<?rfc strict="yes" ?>
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<!-- 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 -->
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<?rfc symrefs="yes"?>
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<?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" ?>
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<?rfc subcompact="no" ?>
<!-- keep one blank line between list items -->
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<rfc category="std" docName="draft-ietf-roll-capabilities-latest" ipr="trust200902">
<!-- category values: std, bcp, info, exp, and historic
ipr values: full3667, noModification3667, noDerivatives3667
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="RPL Capabilities">RPL Capabilities</title>
<author fullname="Rahul Arvind Jadhav" initials="R.A." role="editor" surname="Jadhav">
<address>
<postal>
<street>Marathahalli</street>
<city>Bangalore</city>
<region>Karnataka</region>
<code>560037</code>
<country>India</country>
</postal>
<email>[email protected]</email>
</address>
</author>
<author initials="P" surname="Thubert" fullname="Pascal Thubert">
<organization abbrev="Cisco">Cisco Systems, Inc</organization>
<address>
<postal>
<street>Building D</street>
<street>45 Allee des Ormes - BP1200 </street>
<city>MOUGINS - Sophia Antipolis</city>
<code>06254</code>
<country>France</country>
</postal>
<phone>+33 497 23 26 34</phone>
<email>[email protected]</email>
</address>
</author>
<author initials="M." surname="Richardson" fullname="Michael Richardson">
<organization>Sandelman Software Works</organization>
<address>
<email>[email protected]</email>
</address>
</author>
<author fullname="Rabi Narayan Sahoo" initials="R.N." surname="Sahoo">
<organization>Juniper</organization>
<address>
<email>[email protected]</email>
</address>
</author>
<date/>
<area>Routing</area>
<workgroup>ROLL</workgroup>
<!-- WG name at the upperleft corner of the doc,
IETF is fine for individual submissions.
If this element is not present, the default is "Network Working Group",
which is used by the RFC Editor as a nod to the history of the IETF. -->
<keyword>RPL, mesh, MOP, MOPex, extension, capability, capabilities</keyword>
<!-- Keywords will be incorporated into HTML output
files in a meta tag but they have no effect on text or nroff
output. If you submit your draft to the RFC Editor, the
keywords will be used for the search engine. -->
<abstract>
<t>
This draft enables the discovery, advertisement and query of
capabilities for RPL nodes.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
RPL <xref target="RFC6550"/> specifies a proactive distance-vector
based routing scheme. The protocol creates a DAG-like structure
which operates with a given "Mode of Operation" (MOP) determining the
minimal and mandatory set of primitives to be supported by all the
participating nodes.
</t>
<t>
This document adds a notion of capabilities, through which a node in the
network could inform its peers about its additional capabilities.
Using capabilities, a node could determine whether the target node
supports the required feature before utilizing the feature.
This document highlights the differences between capabilities and
Mode of Operation and explains the necessity for the former.
</t>
<section title="Requirements Language and Terminology">
<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>
MOP: Mode of Operation. Identifies the MOP of the RPL Instance
as administratively provisioned at and distributed by the DODAG
root.
</t>
<t>
MOPex: Extended MOP: As defined in <xref
target="I-D.ietf-roll-mopex"/>.
</t>
<t>
Capabilities: Additional features or capabilities that are
supported by the node.
</t>
<t>
Cap: Abbreviated term used for Capability.
</t>
<t>
Caps: Abbreviated term used for Capabilities.
</t>
<t>
DAO: DODAG Advertisement Object. A RPL (pronounced ripple)
message used to advertise the target information in order to
establish routing adjacencies.
</t>
<t>
DIO: DODAG Information Object. A RPL message initiated by the
root and is used to advertise the network configuration
information.
</t>
<t>
Current parent: Parent 6LR node before switching to the new
path.
</t>
<t>
NPDAO: No-Path DAO. A DAO message that contains a Transit
Information Option with lifetime equal to 0.
</t>
<t>
Upstream path/direction: Path or direction from the node to the
Root in a DAG.
</t>
<t>
Downstream path/direction: Path or direction to the node from
the Root in a DAG.
</t>
<t>
This document uses terminology described in <xref
target="RFC6550"/>. For the sake of readability all the
known relevant terms are repeated in this section.
</t>
</section>
<section anchor="cap-what" title="What are Capabilities?">
<t>
Currently, RPL specification does not have a mechanism whereby a
node can signal the set of features that are available on its
end. Such a mechanism could help the root to advertise its
capabilities and in response also determine some advanced
information about the capabilities of the joining nodes. This
document defines Capabilities and corresponding messaging
handshakes that could be supported by the nodes. Capabilities
are embedded as an RPL Control Message Option as defined in
Section 6.7 of <xref target="RFC6550"/>.
</t>
</section>
</section>
<section anchor="requirements" title="Requirements for this document">
<t>
Following are the requirements considered for this documents:
<list style="format REQ%d:">
<t>
Optional capabilities handshake. Capabilities are features,
possibly optional, which could be indicated between the
nodes and the root within an RPL Instance.
</t>
<t>
Capabilities handshake could be optionally added with
existing MOPs. Capabilities, being optional, could be put
to use with existing MOPs. Capabilities and MOP-extension
are mutually independent i.e. a DIO can have a capabilities
option, MOP-extension option, or both in the same message.
</t>
<t>
Capabilities could be explicitly queried.
</t>
</list>
</t>
<section anchor="cap-why" title="How are Capabilities different from existing RPL primitives?">
<t>
The Mode of Operation (MOP) field in RPL mandates the
operational requirement for the nodes joining as routers. MOP
and DIO Configuration Option is strictly controlled by the Root
node in RPL. Intermediate 6LRs cannot modify these fields.
Also, the MOP never changes for the lifetime of the RPL
Instance. Changes in DIO Configuration Option are possible but
are rare. Capabilities, on the other hand, might change
more dynamically.
</t>
<t>
RPL DIO message also carries routing metrics and constraints as
specified in <xref target="RFC6551"/>. Metrics and constraints
are used in addition to an objective function to determine a node's
rank calculation. A router may use capabilities carried in DIO
messages as additional metrics/constraints. However,
capabilities have a larger scope and might be carried in
messages other than DIO and can flow in either direction
(upstream and downstream).
</t>
</section>
</section>
<section anchor="cap-how" title="Capabilities">
<t>
Handling of Capabilities MUST be supported if the network uses
MOPex <xref target="I-D.ietf-roll-mopex"/>.
</t>
<t>
Note that capabilities and MOPex are mutually exclusive and it is
possible for an implementation to support either or both of the
options.
</t>
<section anchor="cap-option" title="Capability Control Message Option">
<t>
<figure align="center" anchor="cap-opt" title="Capabilities
Option"><artwork align="center"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TODO | Option Length | Capabilities TLVs
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
<t>
Multiple capabilities can be sent in the same message. The
length field allows the message parser to skip the capability
TLV parsing.
</t>
<t>
<figure align="center" anchor="cap-tlv" title="Capabilities
TLV"><artwork align="center"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CapType | Len |J|I|C| Flags | ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
<t>
Every capability is identified by its type and it may have an
optional Capability Info. Note that a given capability may or
may not be disseminated with additional information depending on
the scope of the capability indicated by the I bit.
</t>
<t>
Len: 8-bit unsigned integer, representing the length
in octets of the TLV, not including the CapType, Length and
Flags fields.
</t>
<t>
J = Join only as leaf if capability not understood.
</t>
<t>
I = Ignore the message if this capability is not understood.
</t>
<t>
C = Flag indicating that the capability MUST be copied in the
downstream message.
</t>
</section>
<section anchor="cap-handshake" title="Capabilities Handshake">
<t>
The root node can advertise the set of capabilities it
supports in the DIO message. A node can take advantage of the
knowledge that the root supports a particular capability.
Similarly, a node can advertise its capabilities in the DAO
message using the capability control message option defined in
this document. Capabilities advertised by non-root nodes is
strictly a subset of the capabilities advertised by the root.
</t>
<t>
In storing MOP, the DAO message from the 6LR can contain
multiple target options because of the DAO-Aggregation. The
targets of the capabilities option are indicated by one or more
Target options that precede the Capabilities Option. This
handling is similar to the Transit Information Option as
supported in Section 6.7.8. of <xref target = "RFC6550" />.
</t>
</section>
</section>
<section anchor="caps-query-rsp" title="Querying Capabilities">
<t>
Nodes may be interested in knowing the capabilities of another node
before taking an action. For example, consider
<xref target="I-D.ietf-roll-dao-projection"/>, in which the Root may want to
know the capabilities of the nodes along a network segment before
it initiates a projected DAO to install the routes along that
segment.
</t>
<t>
Caps can be carried in existing RPL Control messages as Control
Options, however, Caps can also be queried explicitly. This section
provides a way for a node to query the capability set of another node.
The capability query and subsequent response messages are directly
addressed between the two peers.
</t>
<!--
<t>
Requirements for capability query procedure:
<list hangIndent="4" style="hanging">
<t hangText="Query subset:">
Possible to query a subset or whole capability set.
</t>
<t hangText="Multi-Message response:">
If the capability set does not fit in a single message then
it should be possible to send it across multiple messages.
</t>
<t hangText="Stateless operation:">
Stateless capability query and response.
</t>
<t hangText="Async Caps update:">
Update the capability asynchronously.
</t>
<t hangText="Handle Node reboots:">
Capability set of a node may change on reboot (for e.g.,
because of firmware update). It should be possible for the
end nodes to determine this change.
</t>
</list>
</t>
-->
<section anchor="caps-query" title="Capability Query (CAPQ)">
<t> <figure align="center" anchor="capq_obj"
title="CAPQ base object"> <artwork align="center"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Flags | reserved | CAPQSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
<t>
<list hangIndent="4" style="hanging">
<!--
<t hangText="NCSS:">
One byte, Node Configuration State Sequence. The
Last-NCSS represents the last known NCSS reported by the
destination node. This value is set to zero if the
last-NCSS is not known.
</t>
-->
<t hangText="CAPQSequence:">
One byte, Sequence number sent by the CAPQ sender and
reflected back by the responder in the CAPS message.
</t>
<t hangText="Flags:">
One byte, set to zero by sender, ignored by receiver.
</t>
<t hangText="reserved:">
One byte, set to zero by sender, ignored by receiver.
</t>
</list>
</t>
<t>
The CAPQ base object may be followed by one or more options. The
Capability Type List Control Option (see <xref target="cap-tlist"/>)
is used to carry a set of capability types to query about.
</t>
<t>
If the sender does not send a Capability Type List Control
Option, this indicates that the node intends to query the
Capability Type List supported by the target node.
</t>
<!--
<t>
NCSS is a sequence counter following the sequence operation
as mentioned in Section 7.2 of RFC6550 and is used by the node to
synchronize the capability set. The querying node will use this
to check if it has the latest capability set from the node. NCSS
may change only if any element of the capability set changes.
Note that NCSS is applicable for the whole capability set and
not individual capability. The idea is that the capability set
will change infrequently hence a common NCSS is sufficient for
all Caps. If the querying node is not aware of the last known
NCSS of the target node then it sets the NCSS to 0.
</t>
-->
<section anchor="capq-opts" title="Capability Type List Control Option">
<t>
<figure align="center" anchor="cap-tlist"
title="Capability Type List Control Option">
<artwork align="center"> <![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TODO | Option Length | CapType1 | CapType2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CapType3 | .....
+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
</section>
<section title="Secure CAPQ">
<t>
A Secure CAPQ message follows the format in <xref
target="RFC6550"/> Figure 7, where the base message
format is the CAPQ message shown in <xref
target="capq_obj"/>.
</t>
</section>
<section title="Base rules for CAPQ handling">
<t>
A CAPQ message may get dropped or lost in the transit. The
sender of CAPQ MAY retry the CAPQ message after some delay.
The delay SHOULD NOT be less than 1 second.
</t>
</section>
</section>
<section anchor="caps-rsp" title="Capability Set Response (CAPS)">
<t> <figure align="center" anchor="caps_obj"
title="CAPS base object"><artwork align="center"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| RPLInstanceID | Flags | Reserved | CAPQSequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option(s)...
+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
<t>
<list hangIndent="4" style="hanging">
<t hangText="Flags:">
One byte, set to zero by sender, ignored by receiver.
</t>
<t hangText="reserved:">
One byte, set to zero by sender, ignored by receiver.
</t>
<t hangText="CAPQSequence:">
One byte, Sequence number copied from CAPQSequence
received in the CAPQ message.
</t>
<!--
<t hangText="CAPQStatus:">
One byte status value indicating status of the
capability query. The status could be 0(indicating
Success) or 1 (indicating subset of queried cap set not
supported). If the status is 1 then the option
<xref target="cap-tlist"/> SHOULD be sent indicating
the cap types which are not supported.
</t>
-->
</list>
</t>
<t>
CAPS message SHOULD contain the capability set
<xref target="cap-opt"/> queried by the CAPQ sender. If
<!-- do you mean caps_obj instead? -->
the target node does not support a subset of the queried
capabilities then the Capability Type List
with the unsupported cap-types SHOULD be sent back
indicating the queried capabilities not-supported by the
target node. For example, check
<xref target="partial-cap"/>
</t>
<t>
If the CAPQ message does not contain any
Capability Type List option then the receiver MUST
respond with the cap types it supports using a Capability Type List Option (see
<xref target="cap-tlist"/>).
</t>
<t>
If the capability set cannot be transmitted in a single message
(for e.g., because of MTU limitations) then multiple CAPS
messages could be used. All the CAPS messages MUST use the same
CAPQSequence number copied from the corresponding CAPQ message.
</t>
<section title="Secure CAPS">
<t>
A Secure CAPS message follows the format in <xref
target="RFC6550"/> Figure 7, where the base message
format is the CAPS message shown in <xref
target="caps_obj"/>.
</t>
</section>
</section>
</section>
<section anchor="caps-guidelines" title="Guidelines for defining new capabilities">
<t>
This section provides guidelines/recommendations towards defining
new capabilities. Note that the capabilities might be carried as
part of the multicast messaging such as DIO and hence the set
should be used sparingly.
</t>
<section anchor="caps-handling-flags" title="Handling Capability flags">
<t>
A node MUST drop or discard the message with an unknown
capability with the 'D' flag set. The message MUST be discarded
silently.
</t>
<t>
The 'J' (join) flag can be set in context to a capability
either by a 6LR or the root. The 'J' flag indicates that if the
capability is not supported by a node then it can join the
instance only as a 6LN (or do not join as 6LR).
</t>
<t>
The 'C' (copy) flag is set by the node indicating that the
capabilities MUST be copied downstream by the node even if the
node does not understand the capability.
</t>
<section anchor="flags-rules" title="Rules to handle capabilities flag">
<t>
<list style="hanging">
<t hangText="How should a node react to capability it does not support before joining the Instance?"><vspace />
On receiving a capability it does not support, the node
MUST check the 'J' flag of the capability before
joining the Instance. If the 'J' flag is set then it
can only join as a 6LN.
</t>
<t hangText="How should a node react to capability it does not support after joining the Instance?"><vspace />
If the node is operating as 6LR and subsequently it
receives a capability from its preferred parent which
it does not understand with 'J' flag set, then the node
has to switch itself to 6LN mode. During switching, the
node needs to inform its downstream peers of its
changed status by sending a DIO with infinite rank as
mentioned in RFC6550. Alternatively, a node may decide
to switch to another parent with compatible and known
capabilities.
</t>
<t hangText="When to use and when not to use Capabilities?"><vspace />
Capabilities are used to indicate a feature that is
supported by the node. Capabilities are not meant for
configuration management for e.g., setting a threshold.
</t>
</list>
</t>
</section>
</section>
</section>
<section anchor="roll-caps" title="Node Capabilities">
<section anchor="cap-ind" title="Capability Indicators">
<t>
Capability Indicators indicate the capabilities supported by
the node in the form of simple flags. Capabilities that do not
need additional information to be specified can make use of
these flags to indicate their support.
</t>
<section title="Format of Capability Indicators">
<t>
<figure align="center" anchor="cap-ind-tlv" title="Capability Indicators TLV">
<artwork align="center"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CapType=0x01 | Len |J|I|C| Flags |T|..Indicators..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
<t>
Flags: LRs MUST set it to 0. I bit will always be set to 0.
</t>
<t>
T flag (Bit 1): Indicates whether the node supports 6LoRH
<xref target="RFC8138"/>.
</t>
</section>
</section>
<section title="Routing Resource Capability">
<t>
Storing Mode of Operation requires each intermediate router
in the LLN to maintain routing state information in the
routing table. LLN routers typically operate with
constraints on processing power, memory, and energy
(battery power). Memory limits the size of the routing state
an LR and BR can maintain. When the routing table of an LR
or BR is full, it will either reject the new DAO messages
received or will use some replacement policy to remove a
routing entry and add the new one. Rejection of DAO
messages will lead to an increase in DAO message
transmission that impacts the energy and network
convergence time. Routing state replacement leads to
downward path downtime.
</t>
<t>
One possible way to solve problems due to routing table
size constraint is to use this information to add neighbors
to the DAO parent set. Routing resource capability can be
used by LR and BR to advertise their current routing table
usage details in the network. LR or LNs in LLN can use this
information in the selection of the DAO parent set. PCE can
use this information to select intermediate routers for the
projected routes. Routing Resource is an optional capability.
</t>
<t>
Routing resource capabablity sent in DIO message has link
local scope and it MUST NOT be forwarded. The 'C' bit of this
capability MUST be set to 0.
</t>
<section title="Format of Routing Resource Capability">
<t>
<figure align="center" anchor="rtres-tlv" title="Routing Resource Capability TLV">
<artwork align="center"><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CapType=0x02 | Len=3 |J|I|C| Flags | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total Capacity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork> </figure>
</t>
<t>
Type: 0x02.
</t>
<t>
Flags: I bit MUST be set to 0. C bit MUST be set to 0.
</t>
<t>
Len: 8-bit unsigned integer, representing the length
in octets of the option, not including the Option Type
and Length/flags fields.
</t>
<t>
Resvd: 8-bit unused field. It MUST be initialized to
zero by the sender and MUST be ignored by the receiver.
</t>
<t>
Total Capacity: 16 bit unsigned integer representing
the routing table size.
</t>
</section>
</section>
<!--
<section title="Neighbor Cache Capability">
<t>
A neighbor cache maintains neighboring one-hop connected
nodes information such as MAC address, link-local IP
address and other reachability state information needed for
layer two communication.Node density has direct
implications on the neighbor cache. In the constrained
network scenario the size of the neighbor cache will be
limited. Thus there are chances that a node may not be able
to store all the neighboring nodes in its cache and use
replacement algorithms to evict some of the entries to
accommodate the new one. If the replaced neighbor has
installed a DAO route on it then it can lead to packet loss
or additional address resolution message exchange. To
avoid unnecessary replacement of neighbor cache entries
neighbor cache management policy <xref
target="I-D.ietf-lwig-nbr-mgmt-policy"/> proposes a
solution that will put a restriction on the connectivity to
immediate neighbor depending upon the type of neighbor.
But this won't solve the problem unless until the
availability of neighbor cache is not taken into
consideration while selecting the DAO parent set.
</t>
<t>
Neighbor Cache capability can be used by LR and BR to
advertise their neighbor cache size information. This
capablity information has only link scope and should not be
advertised in the entire network.
</t>
<section title="Format of Neighbor Cache Capability">
</section>
</section>
-->
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>
Thanks to Georgios Papadopoulos, Li Zhao for early review and
feedback.
</t>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>
IANA is requested to allocate new codes for the CAPQ and CAPS
messages from the RPL Control Codes registry.
</t>
<texttable title="New RPL Control Messages">
<ttcol align='center'>Code</ttcol>
<ttcol align='center'>Description</ttcol>
<ttcol align='center'>Reference</ttcol>
<c>TBD1</c>
<c>Capability Query</c>
<c>This document</c>
<c>TBD2</c>
<c>Capability Response</c>
<c>This document</c>
<c>TBD3</c>
<c>Secure Capability Query</c>
<c>This document</c>
<c>TBD4</c>
<c>Secure Capability Response</c>
<c>This document</c>
</texttable>
<t>
The MSB of the codes allocated to "Secure" messages above should be
set.
</t>
<section title="New option: Capabilities">
<t>
New entry is required for supporting new Capabilities
option and new Capability Type List Option in the "RPL Control
Message Options" space <xref target="RFC6550"/>.
</t>
<texttable title="New options">
<ttcol align='center'>Value</ttcol>
<ttcol align='center'>Meaning</ttcol>
<ttcol align='center'>Reference</ttcol>
<c>TODO</c>
<c>Capability Option</c>
<c>This document</c>
<c>TODO</c>
<c>Capability Type List Option</c>
<c>This document</c>
</texttable>
</section>
<section title="Capability Sub-Type">
<t>
IANA is requested to create a registry for the Capabilities
Type as described in <xref target="cap-tlv"/> of this
document. This registry should be located in TODO. New
Capabilities types may be allocated only by an IETF review.
</t>
<texttable title="Type">
<ttcol align='center'>Value</ttcol>
<ttcol align='center'>Meaning</ttcol>
<ttcol align='center'>Reference</ttcol>
<c>0x01</c>
<c>Capability Indicators</c>
<c>This document</c>
<c>0x02</c>
<c>Routing Resource Capability</c>
<c>This document</c>
</texttable>
</section>
<section title="New Registry for CAPQ Flags">
<t>
IANA is requested to create a registry for the Capabilities
flags as described in <xref target="caps-query"/> of this
document. This registry should be located in TODO. New
Capabilities flags may be allocated only by an IETF review.
Currently no flags are defined by this document. Each value is
tracked with the following qualities:
<list style="symbols">
<t>Flag</t>
<t>Description</t>
<t>Defining RFC</t>
</list>
</t>
</section>
<!--
<section title="New Registry for the CAPQStatus field">
<t>
IANA is requested to create a registry for the 8-bit CAPQ
Status field <xref target="caps-rsp"/>. This registry
should be located in existing category of "Routing Protocol for
Low Power and Lossy Networks (RPL)".
</t>
<t>
New Status values may be allocated only by an IETF Review. Each
value is tracked with the following qualities:
</t>
<t>
<list style="symbols">
<t>Status Code</t>
<t>Description</t>
<t>Defining RFC</t>
</list>
</t>
<t>
The following values are currently defined:
</t>
<texttable title="CAPQStatus Codes">
<ttcol align='center'>Status Code</ttcol>
<ttcol align='center'>Description</ttcol>
<ttcol align='center'>Reference</ttcol>
<c>0</c>
<c>OK</c>
<c>This document</c>
<c>1</c>
<c>Partial or Full queried capability set not supported</c>
<c>This document</c>
</texttable>
</section>
-->
<section title="New Registry for Capabilities Flags">
<t>
IANA is requested to create a registry for the Capabilities
flags as described in <xref target="cap-why"/> of this
document. This registry should be located in TODO. New
Capabilities flags may be allocated only by an IETF review.
Currently no flags are defined by this document. Each value is
tracked with the following qualities:
<list style="symbols">
<t>Flag</t>
<t>Description</t>
<t>Defining RFC</t>
</list>
</t>
</section>
<section title="New Registry for Capabilities Indicators">
<t>
IANA is requested to create a registry for the Capabilities
Indicators as described in <xref target="cap-ind"/> of this
document. This registry should be located in TODO. New
Capabilities indicators may be allocated only by an IETF review.
Each value is tracked with the following qualities:
<list style="symbols">
<t>Flag</t>
<t>Description</t>
<t>Defining RFC</t>
</list>
</t>
</section>
</section>
<section anchor="Security" title="Security Considerations">
<t>
The options defined in this document are carried in the base
message objects as defined in <xref target = "RFC6550" />. The RPL
control message options are protected by the same security
mechanisms that protect the base messages.
</t>
<t>
Capabilities flag can reveal that the node has been upgraded or is
running a old feature set. This document assumes that the base
messages that carry these options are protected by RPL security
mechanisms and thus are not visible to a malicious node.
</t>
<t>
[TODO] implications of malicious attack involving setting the
capability flags.
</t>
</section>
</middle>
<back>
<references title="Normative References">
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?-->
&RFC2119;
&RFC6550;
&RFC8138;
<?rfc include='reference.I-D.ietf-roll-mopex.xml'?>
</references>
<references title="Informative References">
<!-- Here we use entities that we defined at the beginning. -->
&RFC6551;
<?rfc include='reference.I-D.ietf-roll-dao-projection.xml'?>
<!-- <?rfc include='reference.I-D.ietf-lwig-nbr-mgmt-policy.xml'?> -->
</references>
<section anchor="app-additional" title="Capability Handshake Example">
<section title="Query supported Cap Types">
<t>
<figure align="center" anchor="query-cap-types"
title="Query supported Cap Types"><artwork align="center"><![CDATA[
Root 6LR/6LN
| |
| CAPQ(seq=1, opts=nil) |
|---------------------------------->|
| |
| |
| CAPS(seq=1, opts={CapTypeList}) |
|<----------------------------------|
| |
]]></artwork> </figure>
</t>
<t>
CAPQ message with no CapTypeList Option results in the peer
responding with a CAPS message with CapTypeList Option indicating
all the capability set it supports.
</t>
</section>
<section title="Query specific Cap Set">
<t>
<figure align="center" anchor="cap-query-specific-cap"
title="Query specific Cap Set"><artwork align="center"><![CDATA[
Root 6LR/6LN
| |
| CAPQ(seq=2, |
| opts={CapTypeList=[Cap1, Cap2]})|
|---------------------------------->|
| |
| |
| CAPS(seq=2, |
| opts={Cap1=Cap1Value, |
| Cap2=Cap2Value}) |
|<----------------------------------|
| |
]]></artwork> </figure>
</t>
<t>
This flow indicates the case where the Root probes for specific
Capabilities of the peer node and the peer node responds with the
value of indicated Capability set.
</t>
</section>
<section anchor="partial-cap" title="CAPS with partial Cap Set">
<t>
<figure align="center" title="Partial Capability Set handshake">
<artwork align="center"><![CDATA[
Root 6LR/6LN
| |
| CAPQ(seq=3, |
| opts={CapTypeList=[Cap1, Cap2, |
| Cap3, Cap4]})|
|---------------------------------->|
| |
| |
| CAPS(seq=3, |
| opts={Cap2=Cap2Value, |
| Cap3=Cap3Value, |
| CapTypeList=[Cap1,Cap4]})|
|<----------------------------------|
| |
]]></artwork> </figure>
</t>
<t>
Assume that Root queries for capabilities {Cap1, Cap2, Cap3, Cap4}
from the peer node. However the peer node does not support or does
not understand capability {cap1, cap4}. In this case the peer node
will respond back with value of Cap2 and Cap3 (which it understands)
and set the CapTypeList option with {Cap1, Cap4} type.
</t>
</section>
</section>
</back>
</rfc>