Routing for RPL Leaves
draft-thubert-roll-unaware-leaves-03
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft whose latest revision state is "Replaced".
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|
|---|---|---|---|
| Author | Pascal Thubert | ||
| Last updated | 2018-02-23 | ||
| Replaced by | draft-ietf-roll-unaware-leaves, draft-ietf-roll-unaware-leaves, RFC 9010 | ||
| RFC stream | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
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draft-thubert-roll-unaware-leaves-03
ROLL P. Thubert, Ed.
Internet-Draft Cisco
Updates: 6550, 6775 (if approved) February 23, 2018
Intended status: Standards Track
Expires: August 27, 2018
Routing for RPL Leaves
draft-thubert-roll-unaware-leaves-03
Abstract
This specification updates RFC 6550 and RFC 6775 unicast routing
service in a RPL domain to 6LoWPAN ND nodes that do not participate
to the routing protocol.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 August 27, 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Updating RFC 6550 . . . . . . . . . . . . . . . . . . . . . . 4
4. Updating RFC 6775 Update . . . . . . . . . . . . . . . . . . 5
5. Protocol Operations . . . . . . . . . . . . . . . . . . . . . 5
5.1. General Flow . . . . . . . . . . . . . . . . . . . . . . 5
5.2. 6LN Operation . . . . . . . . . . . . . . . . . . . . . . 7
5.3. 6LR Operation . . . . . . . . . . . . . . . . . . . . . . 7
5.4. RPL Root Operation . . . . . . . . . . . . . . . . . . . 8
5.5. 6LBR Operation . . . . . . . . . . . . . . . . . . . . . 9
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Subset of a 6LoWPAN Glossary . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving energy, which is the most constrained resource of
all. Other design constraints, such as a limited memory capacity,
duty cycling of the LLN devices and low-power lossy transmissions,
derive from that primary concern.
The IETF produced the "Routing Protocol for Low Power and Lossy
Networks" [RFC6550] (RPL) to provide routing services within such
constraints. RPL is a Distance-Vector protocol, which, compared to
link-state protocols, limits the amount of topological knowledge that
needs to be installed and maintained in each node. In order to
operate in constrained networks, RPL allows a Routing Stretch (see
[RFC6687]), whereby routing is only performed along a DODAG as
opposed to straight along a shortest path between 2 peers, whatever
that would mean in a given LLN. This trades the quality of peer-to-
peer (P2P) paths for a vastly reduced amount of control traffic and
routing state that would be required to operate a any-to-any shortest
path protocol. Finally, broken routes may be fixed lazily and on-
demand, based on dataplane inconsistency discovery, which avoids
wasting energy in the proactive repair of unused paths.
In order to cope with lossy transmissions, RPL forms Direction-
Oriented Directed Acyclic Graphs (DODAGs) using DODAG Information
Solicitation (DIS) and DODAG Information Object (DIO) messages. For
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most of the nodes, though not all, a DODAG provides multiple
forwarding solutions towards the Root of the topology via so-called
parents. RPL is designed to adapt to fuzzy connectivity, whereby the
physical topology cannot be expected to reach a stable state, with a
lazy control that creates routes proactively but only fixes them when
they are used by actual traffic. It results that RPL provides
reachability for most of the LLN nodes, most of the time, but does
not really converge in the classical sense. RPL provides unicast and
multicast routing services back to RPL-Aware nodes. A RPL-Aware Node
will inject routes to self using Destination Advertisement Object
(DAO) messages sent to either their parents in Storing Mode or to the
Root indicating their parent in Non-Storing mode. This process
effectively forms a DODAG back to the device that is a subset of the
DODAG to the Root with all links reversed.
The IPv6 [RFC8200] Neighbor Discovery (IPv6 ND) Protocol (NDP) suite
[RFC4861] [RFC4862] defined for fast media such a Ethernet, relies
heavily on multicast operations for address discovery and duplicate
address detection (DAD).
"Neighbor Discovery Optimizations for 6LoWPAN networks" [RFC6775]
(6LoWPAN ND) adapts IPv6 ND for operations over energy-constrained
LLNs. In particular, 6LoWPAN ND introduces a unicast host address
registration mechanism that contributes to reduce the use of
multicast messages that are present in the classical IPv6 ND
protocol. 6LoWPAN ND defines a new Address Registration Option (ARO)
that is carried in the unicast Neighbor Solicitation (NS) and
Neighbor Advertisement (NA) messages between the 6LoWPAN Node (6LN)
and the 6LoWPAN Router (6LR). 6LoWPAN ND also defines the Duplicate
Address Request (DAR) and Duplicate Address Confirmation (DAC)
messages between the 6LR and the 6LoWPAN Border Router (6LBR). In an
LLN, the 6LBR is the central repository of all the registered
addresses in its domain.
When a routing protocol such as RPL is used to maintain reachability
within a Non-Broadcast Multi-Access (NBMA) subnet, some nodes may act
as routers and participate to the routing operations whereas others
may be plain hosts. In RPL terms, a plain host that does not
participate to the routing protocol is called a Leaf. It must be
noted that a 6LN could participate to RPL and inject DAO routes to
self, but refrain from advertising DIO and get children. In that
case, the 6LN is still a host but not a Leaf.
An Update to 6LoWPAN ND [I-D.ietf-6lo-rfc6775-update] defines an
Extended ARO (EARO) with a 'R' flag to be used by a 6LN when
registering, to indicate that this 6LN is not a router and that it
will not handle its own reachability. The EARO also includes a
sequence counter called Transaction ID (TID), which maps to the Path
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Sequence Field found in Transit Options in RPL DAO messages. It is a
prerequisite for this specification. The DAR and DAC messages are
also extended as EDAR and EDAC messages respectively.
With this specification, a 6LN that operates as a Leaf uses the 'R'
flag to declare itself as such and the 6LR that accepts the
registration will inject routing information on behalf of the 6LN in
the RPL domain. The packet forwarding operation by the 6LR serving a
Leaf 6LN is described in "When to use RFC 6553, 6554 and IPv6-in-
IPv6" [I-D.ietf-roll-useofrplinfo]. This document adds the
capability by a 6LR to advertise the IPv6 address(es) of the 6LN in
the RPL protocol. Examples of routing-agnostic 6LN may include
lightly-powered sensors such as window smash sensor (alarm system),
or the kinetically powered light switch.
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
The Terminology used in this document is consistent with and
incorporates that described in Terms Used in Routing for Low-Power
and Lossy Networks (LLNs). [RFC7102].
Other terms in use in LLNs are found in Terminology for Constrained-
Node Networks [RFC7228].
A glossary of classical 6LoWPAN acronyms is given in Appendix A.
The term "byte" is used in its now customary sense as a synonym for
"octet".
"RPL", "RPL Packet Information" (RPI) and "RPL Instance", DIO, DAO
and DIS messages are defined in the "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks" [RFC6550] specification.
3. Updating RFC 6550
This document specifies a new behavior whereby a 6LR injects DAO
messages for unicast addresses registered through the updated 6LoWPAN
ND [I-D.ietf-6lo-rfc6775-update] on behalf of 6LN nodes that are not
RPL-aware.
Upon the renewal of a 6lowPAN ND registration, this specification
changes the behavior of the 6LR as follows. If the 'R' flag is set,
the 6LR injects a DAO targeting the Registered Address, and refrains
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from sending a DAR message. the DAR/DAC exchange that refreshes the
state in the 6LBR happens instead between the RPL Root and the 6LBR.
In that flow, the RPL Root acts as a proxy on behalf of the 6LR upon
the reception of the DAO propagation initiated at the 6LR.
4. Updating RFC 6775 Update
This document makes use of the 'R' flag in the EARO option, used by a
6LN, when registering, to indicate that this 6LN is a Leaf, not aware
of the RPL operation in the network, and thus does not participate to
it. The behavior defined in this specification whereby the 6LR that
processes the registration advertises the Registered Address in DAO
messages and bypasses the DAR/DAC process for the renewal of a
registration, is only triggered by an NS(EARO) that has the 'R' flag
set. A RPL Leaf SHOULD set the 'R' flag.
If the 'R' flag is not set, then the Registering Node is expected to
be a RPL router that handles the reachability of the Registered
Address by itself. This document also specifies a keep-alive EDAR
message that the RPL Root may use to maintain an existing state in
the 6LBR upon receiving DAO messages. The EDAR message may only act
as a refresher and can only update the Lifetime and the TID of the
state in the 6LBR. A RPL router SHOULD NOT set the 'R' flag.
5. Protocol Operations
5.1. General Flow
This specification enables to save the exchange of Extended Duplicate
Address messages, EDAR and EDAC, from a 6LN all the way to the 6LBR
across a RPL mesh, for the sole purpose of refreshing an existing
state in the 6LBR. Instead, the EDAR/EDAC exchange is proxied by the
RPL Root upon a DAO message that refreshes the RPL routing state. To
achieve this, the lifetimes and sequence counters in 6LoWPAN ND and
RPL are aligned. In other words, the Path Sequence and the Path
Lifetime in the DAO message are derived from the Transaction ID and
the registration lifetime in the NS(EARO) message from the 6LN.
From the perspective of the 6LN, the registration flow happens
transparently; it is not delayed by the proxy RPL operation, so the
device does not need to wait more whether RPL proxy operation happens
or not. The flows below are RPL Non-Storing Mode examples. In
Storing Mode, the DAO ACK may not be present, and the DAO messages
cascade from child to parent all the way to the DODAG Root.
On the first registration, illustrated in Figure 1, from the
perspective of the 6LR, the Extended Duplicate Address message takes
place as prescribed by [I-D.ietf-6lo-rfc6775-update]. When
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successful, the flow creates a Neighbor Cache Entry (NCE) in the 6LR,
and the 6LR injects the registered address in RPL using DAO/DAO-ACK
exchanges all the way to the RPL DODAG Root. The protocol does not
carry a specific information that the Extended Duplicate Address
messages were already exchanged, so the Root proxies them anyway.
6LN 6LR Root 6LBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR |
| |------------------------------->|
| | |
| | Extended DAC |
| |<-------------------------------|
| NA(EARO) | |
|<---------------| | |
| | DAO | |
| |-------------->| |
| | DAO ACK | |
| |<--------------| |
| | | keep-alive DAR |
| | |--------------->|
| | | keep-alive DAC |
| | |<---------------|
| | | |
Figure 1: First Registration Flow
A re-registration is performed by the 6LN to maintain the NCE in the
6LR alive before lifetime expires. Upon a re-registration, as
illustrated in Figure 1, the 6LR redistributes the NS(EARO) in RPL.
This causes the RPL DODAG Root to refresh the state in the 6LBR with
a keep-alive EDAR message.
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6LN 6LR Root 6LBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| NA(EARO) | | |
|<---------------| | |
| | DAO | |
| |-------------->| |
| | DAO ACK | |
| |<--------------| |
| | | proxy DAR |
| | |--------------->|
| | | proxy DAC |
| | |<---------------|
| | | |
Figure 2: Next Registration Flow
Note that any of the functions 6LR, Root and 6LBR might be collapsed
in a single node, in which case the flow above happens internally,
and possibly through internal API calls as opposed to messaging.
5.2. 6LN Operation
This specification does not alter the operation of a 6LowpAN ND-
compliant 6LN, which is expected to operate as follows:
o The 6LN obtains an IPv6 global address, for instance using
autoconfiguration [RFC4862] based on a Prefix Information Option
(PIO) [RFC4861] found in a Router Advertisement message or by some
other means such as DHCPv6 [RFC3315].
o Once it has formed an address, the 6LN (re)registers its address
periodically, within the Lifetime of the previous registration, as
prescribed by [I-D.ietf-6lo-rfc6775-update].
o Upon each consecutive registration, the 6LN increases the TID
field.
o The 6LN MAY register to more than one 6LR at the same time. In
that case, a same value of TID is used for each registration.
o The 6LN MAY use any of the 6LRs to which it register to forward
its packets.
5.3. 6LR Operation
Also as prescribed by [I-D.ietf-6lo-rfc6775-update], the 6LR
generates a DAR message upon reception of a valid NS(EARO) message
for the registration of a new IPv6 Address by a 6LN. If the
Duplicate Address exchange succeeds, then the 6LR installs a Neighbor
Cache Entry (NCE). If the 'R' flag was set in the EARO of the NS
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message, and this 6LR can manage the reachability of Registered
Address, then the 6LR sets the 'R' flag in the ARO of the response NA
message.
From then on, the 6LN periodically sends a new NS(EARO) to refresh
the NCE state before the lifetime indicated in the EARO expires, with
TID that is incremented each time till it wraps in a lollipop
fashion. As long as the 'R' flag is set and this router can still
manage the reachability of Registered Address, the 6LR keeps setting
the 'R' flag in the ARO of the response NA message, but the exchange
of Duplicate Address messages is skipped.
Upon a successful NS/NA(EARO) exchange: if the 'R' flag was set in
the EARO of the NS message, then the 6LR SHOULD inject the Registered
Address in RPL by sending a DAO message on behalf of the 6LN; else
the 6LR SHOULD refrain from injecting the registered address into
RPL.
The DAO message advertising the Registered Address MUST be
constructed as follows:
o The registered address is placed in a RPL Target Option in the DAO
message as the Target Prefix, and the Prefix Length is set to 128
o the External 'E' flag in the Transit Information Option (TIO)
associated to the Target Option is set to indicate that the 6LR
redistributes an external target into the RPL network
o the Path Lifetime in the TIO is computed from the Lifetime in the
EARO Option to adapt it to the Lifetime Units used in the RPL
operation. Note that if the lifetime is 0, then the 6LR generates
a No-Path DAO message that cleans up the routes down to the
Address of the 6LN.
o the Path Sequence in the TIO is set to the TID value found in the
EARO option.
o Additionally, in Non-Storing Mode the 6LR indicates one of its
global IPv6 unicast addresses as the Parent Address in the TIO.
If a 6LR receives a valid NS(EARO) message with the 'R' flag reset
and the 6LR was redistributing the registered address due to previous
NS(EARO) messages with the flag set, then it MUST stop injecting the
address. It is up to the Registering Node to maintain the
corresponding route from then on, either keeping it active by sending
further DAO messages, or destroying it using a No-Path DAO.
5.4. RPL Root Operation
In RPL Storing Mode of Operation (MOP), the DAO message is propagated
from child to parent all the way to the Root along the DODAG,
populating routing state as it goes. In Non-Storing Mode, The DAO
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message is sent directly to the route. Upon reception of a DAO
message that creates or updates an existing RPL state, the Root
notifies the 6LR using an internal API if they are collocated, or a
proxied DAR/DAC exchange on behalf of the registering node if they
are separated.
In the latter case, the DAR message MUST be constructed as follows:
o The registered address from in the Target Option is placed in the
Registered Address field
o the Owner Unique ID field is set to all ones to indicate that it
is not provided
o the Registration Lifetime in the DAR message is adapted from the
Path Lifetime in the TIO.
o the TID value is set to the Path Sequence in the TIO.
Upon a status in a DAC message that is not "Success", the Root MAY
destroy the formed paths using a No-Path DAO downwards as specified
in [I-D.ietf-roll-efficient-npdao].
In Non-Storing Mode, the outer IPv6 header that is used by the Root
to transport the source routing information in data packets down the
DODAG has the 6LR that serves the 6LN as final destination. This
way, when the final 6LR decapsulates the outer header, it also
removes all the RPL artifacts from the packet.
5.5. 6LBR Operation
Upon reception of a DAR message with the Owner Unique ID field is set
to all ones, the 6LBR checks whether an entry exists for the and
computes whether the TID in the DAR message is fresher than that in
the entry as prescribed in section 4.2.1. of
[I-D.ietf-6lo-rfc6775-update].
If the entry does not exist, the 6LBR does not create the entry, and
answers with a Status "Removed" in the DAC message.
If the entry exists but is not fresher, the 6LBR does not update the
entry, and answers with a Status "Success" in the DAC message.
If the entry exists and the TID in the DAR message is fresher, the
6LBR updates the TID in the entry, and if the lifetime of the entry
is extended by the Registration Lifetime in the DAR message, it also
updates the lifetime of the entry. In that case, the 6LBR replies
with a Status "Success" in the DAC message.
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6. Implementation Status
7. Security Considerations
The LLN nodes depend on the 6LBR and the RPL participants for their
operation. A trust model must be put in place to ensure that the
right devices are acting in these roles, so as to avoid threats such
as black-holing, or bombing attack whereby an impersonated 6LBR would
destroy state in the network by using the "Removed" Status code.
This trust model could be at a minimum based on a Layer-2 access
control, or could provide role validation as well. This is a generic
6LoWPAN requirement, see Req5.1 in Appendix of
[I-D.ietf-6lo-rfc6775-update].
The keep-alive EDAR message does not carry a valid Registration
Unique ID [I-D.ietf-6lo-rfc6775-update] and it cannot be used to
create a binding state in the 6LBR. The 6LBR MUST NOT create an
entry based on a keep-alive EDAR that does not match an existing
entry. All it can do is refresh the lifetime and the TID of an
existing entry.
8. IANA Considerations
This specification has no requirement on IANA.
9. Acknowledgments
The author wishes to thank Michael Richardson and Georgios
Papadopoulos for their early reviews of and contributions to this
document
10. References
10.1. Normative References
[I-D.ietf-6lo-rfc6775-update]
Thubert, P., Nordmark, E., Chakrabarti, S., and C.
Perkins, "An Update to 6LoWPAN ND", draft-ietf-6lo-
rfc6775-update-13 (work in progress), February 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007,
<https://www.rfc-editor.org/info/rfc4861>.
[RFC4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862,
DOI 10.17487/RFC4862, September 2007,
<https://www.rfc-editor.org/info/rfc4862>.
[RFC6550] Winter, T., Ed., Thubert, P., Ed., Brandt, A., Hui, J.,
Kelsey, R., Levis, P., Pister, K., Struik, R., Vasseur,
JP., and R. Alexander, "RPL: IPv6 Routing Protocol for
Low-Power and Lossy Networks", RFC 6550,
DOI 10.17487/RFC6550, March 2012,
<https://www.rfc-editor.org/info/rfc6550>.
[RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C.
Bormann, "Neighbor Discovery Optimization for IPv6 over
Low-Power Wireless Personal Area Networks (6LoWPANs)",
RFC 6775, DOI 10.17487/RFC6775, November 2012,
<https://www.rfc-editor.org/info/rfc6775>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
10.2. Informative References
[I-D.ietf-6lo-ap-nd]
Thubert, P., Sarikaya, B., and M. Sethi, "Address
Protected Neighbor Discovery for Low-power and Lossy
Networks", draft-ietf-6lo-ap-nd-05 (work in progress),
January 2018.
[I-D.ietf-roll-efficient-npdao]
Jadhav, R., Sahoo, R., and Z. Cao, "No-Path DAO
modifications", draft-ietf-roll-efficient-npdao-01 (work
in progress), October 2017.
[I-D.ietf-roll-useofrplinfo]
Robles, I., Richardson, M., and P. Thubert, "When to use
RFC 6553, 6554 and IPv6-in-IPv6", draft-ietf-roll-
useofrplinfo-21 (work in progress), February 2018.
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[IEEEstd802154]
IEEE standard for Information Technology, "IEEE Standard
for Local and metropolitan area networks-- Part 15.4: Low-
Rate Wireless Personal Area Networks (LR-WPANs)".
[RFC3315] Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
C., and M. Carney, "Dynamic Host Configuration Protocol
for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
2003, <https://www.rfc-editor.org/info/rfc3315>.
[RFC6687] Tripathi, J., Ed., de Oliveira, J., Ed., and JP. Vasseur,
Ed., "Performance Evaluation of the Routing Protocol for
Low-Power and Lossy Networks (RPL)", RFC 6687,
DOI 10.17487/RFC6687, October 2012,
<https://www.rfc-editor.org/info/rfc6687>.
[RFC7102] Vasseur, JP., "Terms Used in Routing for Low-Power and
Lossy Networks", RFC 7102, DOI 10.17487/RFC7102, January
2014, <https://www.rfc-editor.org/info/rfc7102>.
[RFC7228] Bormann, C., Ersue, M., and A. Keranen, "Terminology for
Constrained-Node Networks", RFC 7228,
DOI 10.17487/RFC7228, May 2014,
<https://www.rfc-editor.org/info/rfc7228>.
Appendix A. Subset of a 6LoWPAN Glossary
This document often uses the followng acronyms:
6BBR: 6LoWPAN Backbone Router (proxy for the registration)
6LBR: 6LoWPAN Border Router (authoritative on DAD)
6LN: 6LoWPAN Node
6LR: 6LoWPAN Router (relay to the registration process)
6CIO: Capability Indication Option
(E)ARO: (Extended) Address Registration Option
DAD: Duplicate Address Detection
LLN: Low Power Lossy Network (a typical IoT network)
NCE: Neighbor Cache Entry
RUID: Registration Unique ID
TID: Transaction ID (a sequence counter in the EARO)
Author's Address
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Pascal Thubert (editor)
Cisco Systems, Inc
Building D
45 Allee des Ormes - BP1200
MOUGINS - Sophia Antipolis 06254
FRANCE
Phone: +33 497 23 26 34
Email: pthubert@cisco.com
Thubert Expires August 27, 2018 [Page 13]