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draft-ietf-roll-useofrplinfo-20.txt
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ROLL Working Group M. Robles
Internet-Draft Ericsson
Updates: 6553, 6550, 8138 (if approved) M. Richardson
Intended status: Standards Track SSW
Expires: July 26, 2018 P. Thubert
Cisco
January 22, 2018
When to use RFC 6553, 6554 and IPv6-in-IPv6
draft-ietf-roll-useofrplinfo-20
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 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. Additionally, this
document updates the RFC 6553 adding a change to the RPL Option Type
and the RFC 6550 to indicate about this change.
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
working documents as Internet-Drafts. The list of current Internet-
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 26, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
Robles, et al. Expires July 26, 2018 [Page 1]
Internet-Draft Useof6553 January 2018
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology and Requirements Language . . . . . . . . . . . . 4
2.1. hop-by-hop IPv6-in-IPv6 headers . . . . . . . . . . . . . 5
3. Updates to RFC6553, RFC6550 and RFC 8138 . . . . . . . . . . 5
3.1. Updates to RFC 6553 . . . . . . . . . . . . . . . . . . . 5
3.2. Updates to RFC 8138 . . . . . . . . . . . . . . . . . . . 6
3.3. Updates to RFC 6550: Indicating the new RPI in the DODAG
Configuration Option Flag. . . . . . . . . . . . . . . . 7
4. Sample/reference topology . . . . . . . . . . . . . . . . . . 8
5. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Storing mode . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. Storing Mode: Interaction between Leaf and Root . . . . . 14
6.1.1. SM: Example of Flow from RPL-aware-leaf to root . . . 15
6.1.2. SM: Example of Flow from root to RPL-aware-leaf . . . 16
6.1.3. SM: Example of Flow from root to not-RPL-aware-leaf . 16
6.1.4. SM: Example of Flow from not-RPL-aware-leaf to root . 17
6.2. Storing Mode: Interaction between Leaf and Internet . . . 18
6.2.1. SM: Example of Flow from RPL-aware-leaf to Internet . 18
6.2.2. SM: Example of Flow from Internet to RPL-aware-leaf . 18
6.2.3. SM: Example of Flow from not-RPL-aware-leaf to
Internet . . . . . . . . . . . . . . . . . . . . . . 19
6.2.4. SM: Example of Flow from Internet to non-RPL-aware-
leaf . . . . . . . . . . . . . . . . . . . . . . . . 20
6.3. Storing Mode: Interaction between Leaf and Leaf . . . . . 21
6.3.1. SM: Example of Flow from RPL-aware-leaf to RPL-aware-
leaf . . . . . . . . . . . . . . . . . . . . . . . . 21
6.3.2. SM: Example of Flow from RPL-aware-leaf to non-RPL-
aware-leaf . . . . . . . . . . . . . . . . . . . . . 22
6.3.3. SM: Example of Flow from not-RPL-aware-leaf to RPL-
aware-leaf . . . . . . . . . . . . . . . . . . . . . 23
6.3.4. SM: Example of Flow from not-RPL-aware-leaf to not-
RPL-aware-leaf . . . . . . . . . . . . . . . . . . . 24
7. Non Storing mode . . . . . . . . . . . . . . . . . . . . . . 25
7.1. Non-Storing Mode: Interaction between Leaf and Root . . . 26
7.1.1. Non-SM: Example of Flow from RPL-aware-leaf to root . 27
7.1.2. Non-SM: Example of Flow from root to RPL-aware-leaf . 27
7.1.3. Non-SM: Example of Flow from root to not-RPL-aware-
leaf . . . . . . . . . . . . . . . . . . . . . . . . 28
7.1.4. Non-SM: Example of Flow from not-RPL-aware-leaf to
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root . . . . . . . . . . . . . . . . . . . . . . . . 29
7.2. Non-Storing Mode: Interaction between Leaf and Internet . 30
7.2.1. Non-SM: Example of Flow from RPL-aware-leaf to
Internet . . . . . . . . . . . . . . . . . . . . . . 30
7.2.2. Non-SM: Example of Flow from Internet to RPL-aware-
leaf . . . . . . . . . . . . . . . . . . . . . . . . 31
7.2.3. Non-SM: Example of Flow from not-RPL-aware-leaf to
Internet . . . . . . . . . . . . . . . . . . . . . . 32
7.2.4. Non-SM: Example of Flow from Internet to not-RPL-
aware-leaf . . . . . . . . . . . . . . . . . . . . . 33
7.3. Non-Storing Mode: Interaction between Leafs . . . . . . . 34
7.3.1. Non-SM: Example of Flow from RPL-aware-leaf to RPL-
aware-leaf . . . . . . . . . . . . . . . . . . . . . 34
7.3.2. Non-SM: Example of Flow from RPL-aware-leaf to not-
RPL-aware-leaf . . . . . . . . . . . . . . . . . . . 36
7.3.3. Non-SM: Example of Flow from not-RPL-aware-leaf to
RPL-aware-leaf . . . . . . . . . . . . . . . . . . . 37
7.3.4. Non-SM: Example of Flow from not-RPL-aware-leaf to
not-RPL-aware-leaf . . . . . . . . . . . . . . . . . 38
8. Observations about the cases . . . . . . . . . . . . . . . . 38
8.1. Storing mode . . . . . . . . . . . . . . . . . . . . . . 38
8.2. Non-Storing mode . . . . . . . . . . . . . . . . . . . . 39
9. 6LoRH Compression cases . . . . . . . . . . . . . . . . . . . 39
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 40
11. Security Considerations . . . . . . . . . . . . . . . . . . . 40
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 43
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 43
13.1. Normative References . . . . . . . . . . . . . . . . . . 43
13.2. Informative References . . . . . . . . . . . . . . . . . 44
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
1. Introduction
RPL (IPv6 Routing Protocol for Low-Power and Lossy Networks)
[RFC6550] is a routing protocol for constrained networks. RFC 6553
[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 [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
traffic at all which is mostly hop-by-hop traffic (one exception
being DAO messages in non-storing mode).
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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.
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.
The related document A Routing Header Dispatch for 6LoWPAN (6LoRH)
[RFC8138] defines a method to compress RPL Option information and
Routing Header type 3 [RFC6554], an efficient IP-in-IP technique, and
use cases proposed for the [Second6TischPlugtest] involving 6loRH.
2. Terminology and Requirements Language
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 RFC 2119 [RFC2119].
Terminology defined in [RFC7102] applies to this document: LBR, LLN,
RPL, RPL Domain and ROLL.
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.
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.
pledge: a new device which seeks admission to a network. (from
[I-D.ietf-anima-bootstrapping-keyinfra])
Join Registrar and Coordinator (JRC): a device which brings new nodes
(pledges) into a network. (from
[I-D.ietf-anima-bootstrapping-keyinfra])
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 [RFC4192]
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2.1. hop-by-hop IPv6-in-IPv6 headers
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.
3. Updates to RFC6553, RFC6550 and RFC 8138
3.1. Updates to RFC 6553
[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.
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
0x63 01 1 00011 RPL Option [RFC6553]
Figure 1: Option Type in RPL Option.
Recent changes in [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 [RFC8200]). Host systems should do the same, irrespective of the
configuration.
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).
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 ([RFC8200] Section 4.2) if
it doesn't recognize the option type, and the third bit continues to
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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.
This is a significant update to [RFC6553].
Hex Value Binary Value
act chg rest Description Reference
--------- --- --- ------- ----------------- ----------
0x23 00 1 00011 RPL Option [RFCXXXX]
Figure 2: Revised Option Type in RPL Option.
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.
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 [RFC8200]). It allows to the network to be incrementally
upgraded, and for the DODAG root to know which parts of the network
are upgraded.
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.
A network which is switching from straight 6lowpan compression
mechanism to those described in [RFC8138] will experience a flag day
in the data compression anyway, and if possible this change can be
deployed at the same time.
3.2. Updates to RFC 8138
RPI-6LoRH header provides a compressed form for the RPL RPI
[RFC8138]. It should be considered when the Option Type in RPL
Option is decompressed, should take the value of 0x23 instead of
0x63.
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3.3. Updates to RFC 6550: 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 (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.
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.
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.
The DODAG Configuration Option has a Flags field which is modified by
this document. Currently, the DODAG Configuration Option in
[RFC6550] is as follows. .
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.
0 1 2 3
+-----------------+---------------------------------------------------+
| Type = 0x04 | Opt Length = 14| Flags | A | PCS| DIOIntDoubl. |
+---------------------------------------------------------------------+
| DIOIntMin. | DIORedund. | MaxRankIncrease |
+-----------------+---------------------------------------------------+
| MinHopRankIncrease | OCP |
+-----------------+---------------------------------------------------+
|Reserved | Def. Lifetime | Lifetime Unit |
+-----------------+-----------------+---------------------------------+
Figure 3: DODAG Configuration Option.
Bit number three of flag field in the DODAG Configuration option is
to be used as follows:
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+------------+-----------------+---------------+
| Bit number | Description | Reference |
+------------+-----------------+---------------+
| 3 | RPI 0x23 enable | This document |
+------------+-----------------+---------------+
Figure 4: DODAG Configuration Option Flag to indicate the RPI-flag-
day.
In case of rebooting, the node does not remember the flag. Thus, the
DIO is sent with flag indicating the new RPI value.
4. Sample/reference topology
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).
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 showed in Figure 5.
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.
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+--------------+
| Upper Layers |
| |
+--------------+
| RPL |
| |
+--------------+
| ICMPv6 |
| |
+--------------+
| IPv6 |
| |
+--------------+
| 6LoWPAN |
| |
+--------------+
| PHY-MAC |
| |
+--------------+
Figure 5: RPL Stack.
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+------------+
| 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 |
+-------+ +-------+ +------+ +-------+ +-------+
Figure 6: A reference RPL Topology.
Figure 2 shows the reference RPL Topology for this document. The
letters above the nodes are there so that they may be referenced in
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subsequent sections. In the figure, 6LR represents a full router
node. The 6LN is a RPL aware router, or host.
But, the 6LN leaves (Raf - "RPL aware leaf"-) marked as (F, H and I)
are RPL nodes with no children hosts.
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 [RFC6775]. In the document these leafs (G and J) are
also refered to as an IPv6 node.
The 6LBR ("A") in the figure is the root of the Global DODAG.
5. 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.
This document assumes that the LLN is using the no-drop RPI option
(0x23).
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. Section 6.1.4 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. Section 6.2.3 Flow from not-
RPL-aware-leaf to Internet)
The uses cases comprise as follow:
Interaction between Leaf and Root:
RPL-aware-leaf to root
root to RPL-aware-leaf
not-RPL-aware-leaf to root
root to not-RPL-aware-leaf
Interaction between Leaf and Internet:
RPL-aware-leaf to Internet
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Internet to RPL-aware-leaf
not-RPL-aware-leaf to Internet
Internet to not-RPL-aware-leaf
Interaction between Leafs:
RPL-aware-leaf to RPL-aware-leaf (storing and non-storing)
RPL-aware-leaf to not-RPL-aware-leaf (non-storing)
not-RPL-aware-leaf to RPL-aware-leaf (storing and non-storing)
not-RPL-aware-leaf to not-RPL-aware-leaf (non-storing)
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 [RFC2460]. Extensions may not be added or removed except
by the sender or the receiver.
However, unlike [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 [RFC8200]).
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.
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.
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.
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,
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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.
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.
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.
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.
The earlier examples are more extensive to make sure that the process
is clear, while later examples are more concise.
6. Storing mode
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.
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.
In cases where no IP-in-IP header is needed, the column is left
blank.
In all cases the RPI headers are needed, since it identifies
inconsistencies (loops) in the routing topology. In all cases the
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RH3 is not needed because we do not indicate the route in storing
mode.
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.
The leaf can be a router 6LR or a host, both indicated as 6LN (see
Figure 6).
+---------------------+--------------+----------+--------------+
| 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 |
+---------------------+--------------+----------+--------------+
Figure 7: IP-in-IP encapsulation in Storing mode.
6.1. Storing Mode: Interaction between Leaf and Root
In this section we are going to describe the communication flow in
storing mode (SM) between,
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RPL-aware-leaf to root
root to RPL-aware-leaf
not-RPL-aware-leaf to root
root to not-RPL-aware-leaf
6.1.1. SM: Example of Flow from RPL-aware-leaf to root
In storing mode, RFC 6553 (RPI) is used to send RPL Information
instanceID and rank information.
As stated in Section 16.2 of [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.
In this case the flow comprises:
RPL-aware-leaf (6LN) --> 6LR_i --> root(6LBR)
For example, a communication flow could be: Node F --> Node E -->
Node B --> Node A root(6LBR)
As it was mentioned in this document 6LRs, 6LBR are always full-
fledged RPL routers.
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.
No IP-in-IP header is required.
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.
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+-------------------+-----+-------+------+
| Header | 6LN | 6LR_i | 6LBR |
+-------------------+-----+-------+------+
| Inserted headers | RPI | -- | -- |
| Removed headers | -- | -- | RPI |
| Re-added headers | -- | -- | -- |
| Modified headers | -- | RPI | -- |
| Untouched headers | -- | -- | -- |
+-------------------+-----+-------+------+
Storing: Summary of the use of headers from RPL-aware-leaf to root
6.1.2. SM: Example of Flow from root to RPL-aware-leaf
In this case the flow comprises:
root (6LBR) --> 6LR_i --> RPL-aware-leaf (6LN)
For example, a communication flow could be: Node A root(6LBR) -->
Node B --> Node D --> Node F
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.
No IP-in-IP header is required.
+-------------------+------+-------+------+
| Header | 6LBR | 6LR_i | 6LN |
+-------------------+------+-------+------+
| Inserted headers | RPI | -- | -- |
| Removed headers | -- | -- | RPI |
| Re-added headers | -- | -- | -- |
| Modified headers | -- | RPI | -- |
| Untouched headers | -- | -- | -- |
+-------------------+------+-------+------+
Storing: Summary of the use of headers from root to RPL-aware-leaf
6.1.3. SM: Example of Flow from root to not-RPL-aware-leaf
In this case the flow comprises:
root (6LBR) --> 6LR_i --> not-RPL-aware-leaf (IPv6)
For example, a communication flow could be: Node A root(6LBR) -->
Node B --> Node E --> Node G
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As the RPI extension can be ignored by the not-RPL-aware leaf, this
situation is identical to the previous scenario.
+-------------------+------+-------+----------------+
| Header | 6LBR | 6LR_i | IPv6 |
+-------------------+------+-------+----------------+
| Inserted headers | RPI | -- | -- |
| Removed headers | -- | -- | -- |
| Re-added headers | -- | -- | -- |
| Modified headers | -- | RPI | -- |
| Untouched headers | -- | -- | RPI (Ignored) |
+-------------------+------+-------+----------------+
Storing: Summary of the use of headers from root to not-RPL-aware-
leaf
6.1.4. SM: Example of Flow from not-RPL-aware-leaf to root
In this case the flow comprises:
not-RPL-aware-leaf (IPv6) --> 6LR_1 --> 6LR_i --> root (6LBR)
For example, a communication flow could be: Node G --> Node E -->
Node B --> Node A root(6LBR)
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.
+------------+------+---------------+---------------+---------------+
| Header | IPv6 | 6LR_1 | 6LR_i | 6LBR |
+------------+------+---------------+---------------+---------------+
| Inserted | -- | IP-in-IP(RPI) | -- | -- |
| headers | | | | |
| Removed | -- | -- | -- | IP-in-IP(RPI) |
| headers | | | | |
| Re-added | -- | -- | -- | -- |
| headers | | | | |
| Modified | -- | -- | IP-in-IP(RPI) | -- |
| headers | | | | |
| Untouched | -- | -- | -- | -- |
| headers | | | | |
+------------+------+---------------+---------------+---------------+
Storing: Summary of the use of headers from not-RPL-aware-leaf to
root
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6.2. Storing Mode: Interaction between Leaf and Internet
In this section we are going to describe the communication flow in
storing mode (SM) between,
RPL-aware-leaf to Internet
Internet to RPL-aware-leaf
not-RPL-aware-leaf to Internet
Internet to not-RPL-aware-leaf
6.2.1. SM: Example of Flow from RPL-aware-leaf to Internet
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.
In this case the flow comprises:
RPL-aware-leaf (6LN) --> 6LR_i --> root (6LBR) --> Internet
For example, the communication flow could be: Node F --> Node D -->
Node B --> Node A root(6LBR) --> Internet
No IP-in-IP header is required.
Note: In this use case we use a node as leaf, but this use case can
be also applicable to any RPL-node type (e.g. 6LR)
+-------------------+------+-------+------+----------------+
| Header | 6LN | 6LR_i | 6LBR | Internet |
+-------------------+------+-------+------+----------------+
| Inserted headers | RPI | -- | -- | -- |
| Removed headers | -- | -- | -- | -- |
| Re-added headers | -- | -- | -- | -- |
| Modified headers | -- | RPI | -- | -- |
| Untouched headers | -- | -- | RPI | RPI (Ignored) |
+-------------------+------+-------+------+----------------+
Storing: Summary of the use of headers from RPL-aware-leaf to
Internet
6.2.2. SM: Example of Flow from Internet to RPL-aware-leaf