6lo P. Thubert, Ed.
Internet-Draft cisco
Updates: 6775 (if approved) E. Nordmark
Intended status: Standards Track
Expires: April 16, 2018 S. Chakrabarti
C. Perkins
Futurewei
October 13, 2017
An Update to 6LoWPAN ND
draft-ietf-6lo-rfc6775-update-10
Abstract
This specification updates RFC 6775 - 6LoWPAN Neighbor Discovery, to
clarify the role of the protocol as a registration technique,
simplify the registration operation in 6LoWPAN routers, as well as to
provide enhancements to the registration capabilities and mobility
detection for different network topologies including the backbone
routers performing proxy Neighbor Discovery in a low power network.
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 April 16, 2018.
Copyright Notice
Copyright (c) 2017 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
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publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability of Address Registration Options . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Updating RFC 6775 . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Extended Address Registration Option (EARO) . . . . . . . 7
4.2. Transaction ID . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Comparing TID values . . . . . . . . . . . . . . . . 7
4.3. Owner Unique ID . . . . . . . . . . . . . . . . . . . . . 9
4.4. Extended Duplicate Address Messages . . . . . . . . . . . 10
4.5. Registering the Target Address . . . . . . . . . . . . . 10
4.6. Link-Local Addresses and Registration . . . . . . . . . . 11
4.7. Maintaining the Registration States . . . . . . . . . . . 12
5. Detecting Enhanced ARO Capability Support . . . . . . . . . . 14
6. Extended ND Options And Messages . . . . . . . . . . . . . . 14
6.1. Enhanced Address Registration Option (EARO) . . . . . . . 14
6.2. Extended Duplicate Address Message Formats . . . . . . . 17
6.3. New 6LoWPAN Capability Bits in the Capability Indication
Option . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. Backward Compatibility . . . . . . . . . . . . . . . . . . . 18
7.1. Discovering the capabilities of an ND peer . . . . . . . 18
7.1.1. Using the "E" Flag in the 6CIO . . . . . . . . . . . 19
7.1.2. Using the "T" Flag in the EARO . . . . . . . . . . . 19
7.2. Legacy 6LoWPAN Node . . . . . . . . . . . . . . . . . . . 20
7.3. Legacy 6LoWPAN Router . . . . . . . . . . . . . . . . . . 20
7.4. Legacy 6LoWPAN Border Router . . . . . . . . . . . . . . 21
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 22
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
10.1. ARO Flags . . . . . . . . . . . . . . . . . . . . . . . 23
10.2. ICMP Codes . . . . . . . . . . . . . . . . . . . . . . . 23
10.3. New ARO Status values . . . . . . . . . . . . . . . . . 24
10.4. New 6LoWPAN capability Bits . . . . . . . . . . . . . . 25
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 25
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 25
12.1. Normative References . . . . . . . . . . . . . . . . . . 25
12.2. Informative References . . . . . . . . . . . . . . . . . 26
12.3. External Informative References . . . . . . . . . . . . 29
Appendix A. Applicability and Requirements Served . . . . . . . 30
Appendix B. Requirements . . . . . . . . . . . . . . . . . . . . 30
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B.1. Requirements Related to Mobility . . . . . . . . . . . . 31
B.2. Requirements Related to Routing Protocols . . . . . . . . 31
B.3. Requirements Related to the Variety of Low-Power Link
types . . . . . . . . . . . . . . . . . . . . . . . . . . 32
B.4. Requirements Related to Proxy Operations . . . . . . . . 33
B.5. Requirements Related to Security . . . . . . . . . . . . 33
B.6. Requirements Related to Scalability . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35
1. Introduction
The scope of this draft is an IPv6 Low Power Networks including star
and mesh topologies. This specification modifies and extends the
behavior and protocol elements of "Neighbor Discovery Optimization
for IPv6 over Low-Power Wireless Personal Area Networks" (6LoWPAN ND)
[RFC6775] to enable additional capabilities and enhancements such as:
o Support for indicating mobility vs retry (T-bit)
o Reduce requirement of registration for link-local addresses
o Enhancement to Address Registration Option (ARO)
o Permitting registration of a target address
o Clarification of support of privacy and temporary addresses
The applicability of 6LoWPAN ND registration is discussed in
Section 2, and new extensions and updates to [RFC6775] are presented
in Section 4. Considerations on Backward Compatibility, Security and
Privacy are also elaborated upon in Section 7, Section 8 and in
Section 9, respectively.
2. Applicability of Address Registration Options
The purpose of the Address Registration Option (ARO) in the legacy
6LoWPAN ND specification is to facilitate duplicate address detection
(DAD) for hosts as well as populate Neighbor Cache Entries (NCE)
[RFC4861] in the routers. This reduces the reliance on multicast
operations, which are often as intrusive as broadcast, in IPv6 ND
operations.
With this specification, a failed or useless registration can be
detected for reasons other than address duplication. Examples
include: the router having run out of space; a registration bearing a
stale sequence number perhaps denoting a movement of the host after
the registration was placed; a host misbehaving and attempting to
register an invalid address such as the unspecified address
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[RFC4291]; or a host using an address which is not topologically
correct on that link.
In such cases the host will receive an error to help diagnose the
issue and may retry, possibly with a different address, and possibly
registering to a different router, depending on the returned error.
The ability to return errors to address registrations is not intended
to be used to restrict the ability of hosts to form and use
addresses, as recommended in "Host Address Availability
Recommendations" [RFC7934].
In particular, the freedom to form and register addresses is needed
for enhanced privacy; each host may register a number of addresses
using mechanisms such as "Privacy Extensions for Stateless Address
Autoconfiguration (SLAAC) in IPv6" [RFC4941].
In IPv6 ND [RFC4861], a router must have enough storage to hold
neighbor cache entries for all the addresses to which it may forward.
A router using the Address Registration mechanism also needs enough
storage to hold NCEs for all the addresses that may be registered to
it, regardless of whether or not they are actively communicating.
The number of registrations supported by a 6LoWPAN Router (6LR) or
6LoWPAN Border Router (6LBR) must be clearly documented.
A network administrator should deploy updated 6LR/6LBRs to support
the number and type of devices in his network, based on the number of
IPv6 addresses that those devices require and their address renewal
rate and behaviour.
3. Terminology
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 [RFC2119].
Readers are expected to be familiar with all the terms and concepts
that are discussed in
o "Neighbor Discovery for IP version 6" [RFC4861],
o "IPv6 Stateless Address Autoconfiguration" [RFC4862],
o "IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals" [RFC4919],
o "Neighbor Discovery Optimization for Low-power and Lossy Networks"
[RFC6775] and
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o "Multi-link Subnet Support in IPv6"
[I-D.ietf-ipv6-multilink-subnets],
as well as the following terminology:
Backbone Link: An IPv6 transit link that interconnects two or more
Backbone Routers. It is expected to be a higher speed device
speed compared to the LLN in order to carry the traffic that is
required to federate multiple segments of the potentially large
LLN into a single IPv6 subnet.
Backbone Router: A logical network function in an IPv6 router that
federates a LLN over a Backbone Link. In order to do so, the
Backbone Router (6BBR) proxies the 6LoWPAN ND operations
detailed in the document onto the matching operations that run
over the backbone, typically IPv6 ND. Note that 6BBR is a
logical function, just like 6LR and 6LBR, and that a same
physical router may operate all three.
Extended LLN: The aggregation of multiple LLNs as defined in
[RFC4919], interconnected by a Backbone Link via Backbone
Routers, and forming a single IPv6 MultiLink Subnet.
Registration: The process during which a 6LN registers its
address(es) with the Border Router so the 6BBR can serve as
proxy for ND operations over the Backbone.
Binding: The association between an IP address with a MAC address, a
port and/or other information about the node that owns the IP
address.
Registered Node: The node for which the registration is performed,
and which owns the fields in the EARO option.
Registering Node: The node that performs the registration to the
6BBR, which may proxy for the registered node.
Registered Address: An address owned by the Registered Node node
that was or is being registered.
IPv6 ND: The IPv6 Neighbor Discovery protocol as specified in
[RFC4861] and [RFC4862].
legacy: a 6LN, a 6LR or a 6LBR that supports [RFC6775] but not this
specification.
updated: a 6LN, a 6LR or a 6LBR that supports this specification.
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4. Updating RFC 6775
This specification introduces the Extended Address Registration
Option (EARO) based on the ARO as defined in [RFC6775]; in particular
a "T" flag is added that MUST be set in NS messages when this
specification is used, and echoed in NA messages to confirm that the
protocol is supported.
The extensions to the ARO option are used in the Duplicate Address
Request (DAR) and Duplicate Address Confirmation (DAC) messages, so
as to convey the additional information all the way to the 6LBR. In
turn the 6LBR may proxy the registration using IPv6 ND over a
backbone as illustrated in Figure 1. Note that this specification
avoids the extended DAR flow for Link Local Addresses in Route-Over
mode.
6LN 6LR 6LBR 6BBR
| | | |
| NS(EARO) | | |
|--------------->| | |
| | Extended DAR | |
| |-------------->| |
| | | |
| | | proxy NS(EARO) |
| | |--------------->|
| | | | NS(DAD)
| | | | ------>
| | | | <wait>
| | | |
| | | proxy NA(EARO) |
| | |<---------------|
| | Extended DAC | |
| |<--------------| |
| NA(EARO) | | |
|<---------------| | |
| | | |
Figure 1: (Re-)Registration Flow
In order to support various types of link layers, it is RECOMMENDED
to allow multiple registrations, including for privacy / temporary
addresses, and provides new mechanisms to help clean up stale
registration states as soon as possible.
A Registering Node SHOULD prefer registering to a 6LR that is found
to support this specification, as discussed in Section 7.1, over a
legacy one.
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4.1. Extended Address Registration Option (EARO)
The Extended ARO (EARO) deprecates the ARO and is backward compatible
with it. More details on backward compatibility can be found in
Section 7.
The semantics of the ARO are modified as follows:
o The address that is being registered with a Neighbor Solicitation
(NS) with an EARO is now the Target Address, as opposed to the
Source Address as specified in [RFC6775] (see Section 4.5). This
change enables a 6LBR to use one of its addresses as source to the
proxy-registration of an address that belongs to a LLN Node to a
6BBR. This also limits the use of an address as source address
before it is registered and the associated DAD process is
complete.
o The Unique ID in the EARO Option is not required to be a MAC
address (see Section 4.3).
o The specification introduces a Transaction ID (TID) field in the
EARO (see Section 4.2). The TID MUST be provided by a node that
supports this specification and a new "T" flag MUST be set to
indicate so.
o Finally, this specification introduces new status codes to help
diagnose the cause of a registration failure (see Table 1).
4.2. Transaction ID
The Transaction ID (TID) is a sequence number that is incremented
with each re-registration. The TID is used to detect the freshness
of the registration request and useful to detect one single
registration by multiple 6LOWPAN border routers (e.g., 6LBRs and
6BBRs) supporting the same 6LOWPAN. The TID may also be used by the
network to track the sequence of movements of a node in order to
route to the current (freshest known) location of a moving node.
When a Registered Node is registered with multiple BBRs in parallel,
the same TID SHOULD be used, to enable the 6BBRs to determine that
the registrations are the same, and distinguish that situation from a
movement.
4.2.1. Comparing TID values
The TID is a sequence counter and its operation is the exact match of
the path sequence specified in RPL, the IPv6 Routing Protocol for
Low-Power and Lossy Networks [RFC6550] specification.
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In order to keep this document self-contained and yet compatible, the
text below is an exact copy from section 7.2. "Sequence Counter
Operation" of [RFC6550].
A TID is deemed to be fresher than another when its value is greater
per the operations detailed in this section.
The TID range is subdivided in a 'lollipop' fashion ([Perlman83]),
where the values from 128 and greater are used as a linear sequence
to indicate a restart and bootstrap the counter, and the values less
than or equal to 127 used as a circular sequence number space of size
128 as in [RFC1982]. Consideration is given to the mode of operation
when transitioning from the linear region to the circular region.
Finally, when operating in the circular region, if sequence numbers
are detected to be too far apart then they are not comparable, as
detailed below.
A window of comparison, SEQUENCE_WINDOW = 16, is configured based on
a value of 2^N, where N is defined to be 4 in this specification.
For a given sequence counter,
1. The sequence counter SHOULD be initialized to an implementation
defined value which is 128 or greater prior to use. A
recommended value is 240 (256 - SEQUENCE_WINDOW).
2. When a sequence counter increment would cause the sequence
counter to increment beyond its maximum value, the sequence
counter MUST wrap back to zero. When incrementing a sequence
counter greater than or equal to 128, the maximum value is 255.
When incrementing a sequence counter less than 128, the maximum
value is 127.
3. When comparing two sequence counters, the following rules MUST be
applied:
1. When a first sequence counter A is in the interval [128..255]
and a second sequence counter B is in [0..127]:
1. If (256 + B - A) is less than or equal to
SEQUENCE_WINDOW, then B is greater than A, A is less than
B, and the two are not equal.
2. If (256 + B - A) is greater than SEQUENCE_WINDOW, then A
is greater than B, B is less than A, and the two are not
equal.
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For example, if A is 240, and B is 5, then (256 + 5 - 240) is
21. 21 is greater than SEQUENCE_WINDOW (16), thus 240 is
greater than 5. As another example, if A is 250 and B is 5,
then (256 + 5 - 250) is 11. 11 is less than SEQUENCE_WINDOW
(16), thus 250 is less than 5.
2. In the case where both sequence counters to be compared are
less than or equal to 127, and in the case where both
sequence counters to be compared are greater than or equal to
128:
1. If the absolute magnitude of difference between the two
sequence counters is less than or equal to
SEQUENCE_WINDOW, then a comparison as described in
[RFC1982] is used to determine the relationships greater
than, less than, and equal.
2. If the absolute magnitude of difference of the two
sequence counters is greater than SEQUENCE_WINDOW, then a
desynchronization has occurred and the two sequence
numbers are not comparable.
4. If two sequence numbers are determined to be not comparable, i.e.
the results of the comparison are not defined, then a node should
consider the comparison as if it has evaluated in such a way so
as to give precedence to the sequence number that has most
recently been observed to increment. Failing this, the node
should consider the comparison as if it has evaluated in such a
way so as to minimize the resulting changes to its own state.
4.3. Owner Unique ID
The Owner Unique ID (OUID) enables a duplicate address registration
to be distinguished from a double registration or a movement. An ND
message from the 6BBR over the Backbone that is proxied on behalf of
a Registered Node must carry the most recent EARO option seen for
that node. A NS/NA with an EARO and a NS/NA without a EARO thus
represent different nodes; if they relate to a same target then an
address duplication is likely.
The Owner Unique ID in [RFC6775] is a EUI-64 preconfigured address,
under the assumption that duplicate EUI-64 addresses are avoided.
With this specification, the Owner Unique ID is allowed to be
extended to different types of identifier, as long as the type is
clearly indicated. For instance, the type can be a cryptographic
string and used to prove the ownership of the registration as
discussed in "Address Protected Neighbor Discovery for Low-power and
Lossy Networks" [I-D.ietf-6lo-ap-nd].
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The node SHOULD store the unique ID, or a way to generate that ID, in
persistent memory. Otherwise, if a reboot causes a loss of memory,
re-registering the same address could be impossible until the 6LBR
times out the previous registration.
4.4. Extended Duplicate Address Messages
In order to map the new EARO content in the DAR/DAC messages, a new
TID field is added to the Extended DAR (EDAR) and the Extended DAC
(EDAC) messages as a replacement to a Reserved field, and an odd
value of the ICMP Code indicates support for the TID, to transport
the "T" flag.
In order to prepare for future extensions, and though no option has
been defined for the Duplicate Address messages, implementations
SHOULD expect ND options after the main body, and SHOULD ignore them.
As for the EARO, the Extended Duplicate Address messages are backward
compatible with the legacy versions, and remarks concerning backwards
compatibility for the protocol between the 6LN and the 6LR apply
similarly between a 6LR and a 6LBR.
4.5. Registering the Target Address
The Registering Node is the node that performs the registration to
the 6BBR. As in [RFC6775], it may be the Registered Node as well, in
which case it registers one of its own addresses, and indicates its
own MAC Address as Source Link Layer Address (SLLA) in the NS(EARO).
This specification adds the capability to proxy the registration
operation on behalf of a Registered Node that is reachable over a LLN
mesh. In that case, if the Registered Node is reachable from the
6BBR over a Mesh-Under mesh, the Registering Node indicates the MAC
Address of the Registered Node as SLLA in the NS(EARO). If the
Registered Node is reachable over a Route-Over mesh from the
Registering Node, the SLLA in the NS(ARO) is that of the Registering
Node. This enables the Registering Node to attract the packets from
the 6BBR and route them over the LLN to the Registered Node.
In order to enable the latter operation, this specification changes
the behavior of the 6LN and the 6LR so that the Registered Address is
found in the Target Address field of the NS and NA messages as
opposed to the Source Address. With this convention, a TLLA option
indicates the link-layer address of the 6LN that owns the address,
whereas the SLLA Option in a NS message indicates that of the
Registering Node, which can be the owner device, or a proxy.
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The Registering Node is reachable from the 6LR, and is also the one
expecting packets for the 6LN. Therefore, it MUST place its own Link
Layer Address in the SLLA Option that MUST always be placed in a
registration NS(EARO) message. This maintains compatibility with
legacy 6LoWPAN ND [RFC6775].
4.6. Link-Local Addresses and Registration
Considering that LLN nodes are often not wired and may move, there is
no guarantee that a Link-Local address stays unique between a
potentially variable and unbounded set of neighboring nodes.
Compared to [RFC6775], this specification only requires that a Link-
Local address is unique from the perspective of the two nodes that
use it to communicate (e.g. the 6LN and the 6LR in an NS/NA
exchange). This simplifies the DAD process in Route-Over Mode for
Link-Local addresses, and there is no exchange of Duplicate Address
messages between the 6LR and a 6LBR for Link-Local addresses.
In more details:
An exchange between two nodes using Link-Local addresses implies that
they are reachable over one hop and that at least one of the 2 nodes
acts as a 6LR. A node MUST register a Link-Local address to a 6LR in
order to obtain reachability from that 6LR beyond the current
exchange, and in particular to use the Link-Local address as source
address to register other addresses, e.g. global addresses.
If there is no collision with an address previously registered to
this 6LR by another 6LN, then the Link-Local address is unique from
the standpoint of this 6LR and the registration is acceptable.
Alternatively, two different 6LRs might expose the same Link-Local
address but different link-layer addresses. In that case, a 6LN MUST
only interact with one of the 6LRs.
The DAD process between the 6LR and a 6LBR, which is based on an
exchange of Duplicate Address messages, does not need to take place
for Link-Local addresses.
It is preferable for a 6LR to avoid modifying its state associated to
the Source Address of an NS(EARO) message. For that reason, when
possible, an address that is already registered with a 6LR SHOULD be
used by a 6LN.
When registering to a 6LR that conforms this specification, a node
MUST use a Link-Local address as the source address of the
registration, whatever the type of IPv6 address that is being
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registered. That Link-Local Address MUST be either already
registered, or the address that is being registered.
When a Registering Node does not have an already-Registered Address,
it MUST register a Link-Local address, using it as both the Source
and the Target Address of an NS(EARO) message. In that case, it is
RECOMMENDED to use a Link-Local address that is (expected to be)
globally unique, e.g., derived from a globally unique hardware MAC
address. An EARO option in the response NA indicates that the 6LR
supports this specification.
Since there is no Duplicate Address exchange for Link-Local
addresses, the 6LR may answer immediately to the registration of a
Link-Local address, based solely on its existing state and the Source
Link-Layer Option that MUST be placed in the NS(EARO) message as
required in [RFC6775].
A node needs to register its IPv6 Global Unicast IPv6 Addresses
(GUAs) to a 6LR in order to establish global reachability for these
addresses via that 6LR. When registering with an updated 6LR, a
Registering Node does not use its GUA as Source Address, in contrast
to a node that complies to [RFC6775]. For non-Link-Local addresses,
the Duplicate Address exchange MUST conform to [RFC6775], but the
extended formats described in this specification for the DAR and the
DAC are used to relay the extended information in the case of an
EARO.
4.7. Maintaining the Registration States
This section discusses protocol actions that involve the Registering
Node, the 6LR and the 6LBR. It must be noted that the portion that
deals with a 6LBR only applies to those addresses that are registered
to it; as discussed in Section 4.6, this is not the case for Link-
Local addresses. The registration state includes all data that is
stored in the router relative to that registration, in particular,
but not limited to, an NCE in a 6LR. 6LBRs and 6BBRs may store
additional registration information in more complex data structures
and use protocols that are out of scope of this document to keep them
synchonized when they are distributed.
When its Neighbor Cache is full, a 6LR cannot accept a new
registration. In that situation, the EARO is returned in a NA
message with a Status of 2, and the Registering Node may attempt to
register to another 6LR.
If the registry in the 6LBR is be saturated, in which case the LBR
cannot guarantee that a new address is effectively not a duplicate.
In that case, the 6LBR replies to a EDAR message with a EDAC message
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that carries a Status code 9 indicating "6LBR Registry saturated",
and the address stays in TENTATIVE state. Note: this code is used by
6LBRs instead of Status 2 when responding to a Duplicate Address
message exchange and passed on to the Registering Node by the 6LR.
There is no point for the node to retry this registration immediately
via another 6LR, since the problem is global to the network. The
node may either abandon that address, deregister other addresses
first to make room, or keep the address in TENTATIVE state and retry
later.
A node renews an existing registration by sending a new NS(EARO)
message for the Registered Address. In order to refresh the
registration state in the 6LBR, the registration MUST be reported to
the 6LBR.
A node that ceases to use an address SHOULD attempt to deregister
that address from all the 6LRs to which it has registered the
address, which is achieved using an NS(EARO) message with a
Registration Lifetime of 0.
A node that moves away from a particular 6LR SHOULD attempt to
deregister all of its addresses registered to that 6LR and register
to a new 6LR with an incremented TID. When/if the node shows up
elsewhere, an asynchronous NA(EARO) or EDAC message with a status of
3 "Moved" SHOULD be used to clean up the state in the previous
location. For instance, the "Moved" status can be used by a 6BBR in
a NA(EARO) message to indicate that the ownership of the proxy state
on the Backbone was transferred to another 6BBR, as the consequence
of a movement of the device. The receiver of the message SHOULD
propagate the status down the chain towards the Registered node and
clean up its state.
Upon receiving a NS(EARO) message with a Registration Lifetime of 0
and determining that this EARO is the freshest for a given NCE (see
Section 4.2), a 6LR cleans up its NCE. If the address was registered
to the 6LBR, then the 6LR MUST report to the 6LBR, through a
Duplicate Address exchange with the 6LBR, or an alternate protocol,
indicating the null Registration Lifetime and the latest TID that
this 6LR is aware of.
Upon receiving the Extended DAR message, the 6LBR evaluates if this
is the most recent TID it has received for that particular registry
entry. If so, then the entry is scheduled to be removed, and the
EDAR is answered with a EDAC message bearing a Status of 0
("Success"). Otherwise, a Status 3 ("Moved") is returned instead,
and the existing entry is maintained.
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When an address is scheduled to be removed, the 6LBR SHOULD keep its
entry in a DELAY state for a configurable period of time, so as to
protect a mobile node that deregistered from one 6LR and did not
register yet to a new one, or the new registration did not reach yet
the 6LBR due to propagation delays in the network. Once the DELAY
time is passed, the 6LBR removes silently its entry.
5. Detecting Enhanced ARO Capability Support
The "Generic Header Compression for IPv6 over 6LoWPANs" [RFC7400]
introduces the 6LoWPAN Capability Indication Option (6CIO) to
indicate a node's capabilities to its peers. This specification
extends the format defined in [RFC7400] to signal support for EARO,
as well as the node's capability to act as a 6LR, 6LBR and 6BBR.
The 6CIO is typically sent in a Router Solicitation (RS) message.
When used to signal capabilities per this specification, the 6CIO is
typically present in Router Advertisement (RA) messages but can also
be present in RS, Neighbor Solicitation (NS) and Neighbor
Advertisement (NA) messages.
6. Extended ND Options And Messages
This specification does not introduce new options, but it modifies
existing ones and updates the associated behaviors as specified in
the following subsections.
6.1. Enhanced Address Registration Option (EARO)
The Address Registration Option (ARO) is defined in section 4.1. of
[RFC6775].
The Enhanced Address Registration Option (EARO) updates the ARO
option within Neighbor Discovery NS and NA messages between a 6LN and
its 6LR. On the other hand, the Extended Duplicate Address messages,
EDAR and EDAC, replace the DAR and DAC messages so as to transport
the new information between 6LRs and 6LBRs across LLNs meshes such as
6TiSCH networks.
An NS message with an EARO option is a registration if and only if it
also carries an SLLAO option. The EARO option also used in NS and NA
messages between Backbone Routers over the Backbone link to sort out
the distributed registration state; in that case, it does not carry
the SLLAO option and is not confused with a registration.
When using the EARO option, the address being registered is found in
the Target Address field of the NS and NA messages.
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The EARO extends the ARO and is indicated by the "T" flag set. The
format of the EARO option is as follows:
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 | Length = 2 | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |T| TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or equivalent) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: EARO
Option Fields
Type: 33
Length: 8-bit unsigned integer. The length of the option in
units of 8 bytes. Always 2.
Status: 8-bit unsigned integer. Indicates the status of a
registration in the NA response. MUST be set to 0 in
NS messages. See Table 1 below.
+-------+-----------------------------------------------------------+
| Value | Description |
+-------+-----------------------------------------------------------+
| 0..2 | See [RFC6775]. Note: a Status of 1 "Duplicate Address" |
| | applies to the Registered Address. If the Source Address |
| | conflicts with an existing registration, "Duplicate |
| | Source Address" should be used. |
| | |
| 3 | Moved: The registration fails because it is not the |
| | freshest. This Status indicates that the registration is |
| | rejected because another more recent registration was |
| | done, as indicated by a same OUI and a more recent TID. |
| | One possible cause is a stale registration that has |
| | progressed slowly in the network and was passed by a more |
| | recent one. It could also indicate a OUI collision. |
| | |
| 4 | Removed: The binding state was removed. This may be |
| | placed in an asynchronous NS(ARO) message, or as the |
| | rejection of a proxy registration to a Backbone Router |
| | |
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| 5 | Validation Requested: The Registering Node is challenged |
| | for owning the Registered Address or for being an |
| | acceptable proxy for the registration. This Status is |
| | expected in asynchronous messages from a registrar (6LR, |
| | 6LBR, 6BBR) to indicate that the registration state is |
| | removed, for instance due to a movement of the device. |
| | |
| 6 | Duplicate Source Address: The address used as source of |
| | the NS(ARO) conflicts with an existing registration. |
| | |
| 7 | Invalid Source Address: The address used as source of the |
| | NS(ARO) is not a Link-Local address as prescribed by this |
| | document. |
| | |
| 8 | Registered Address topologically incorrect: The address |
| | being registered is not usable on this link, e.g. it is |
| | not topologically correct |
| | |
| 9 | 6LBR Registry saturated: A new registration cannot be |
| | accepted because the 6LBR Registry is saturated. Note: |
| | this code is used by 6LBRs instead of Status 2 when |
| | responding to a Duplicate Address message exchange and |
| | passed on to the Registering Node by the 6LR. |
| | |
| 10 | Validation Failed: The proof of ownership of the |
| | registered address is not correct. |
+-------+-----------------------------------------------------------+
Table 1: EARO Status
Reserved: This field is unused. It MUST be initialized to zero
by the sender and MUST be ignored by the receiver.
T: One bit flag. Set if the next octet is a used as a
TID.
TID: 1-byte integer; a transaction id that is maintained
by the node and incremented with each transaction.
The node SHOULD maintain the TID in a persistent
storage.
Registration Lifetime: 16-bit integer; expressed in minutes. 0
means that the registration has ended and the
associated state should be removed.
Owner Unique Identifier (OUI): A globally unique identifier for the
node associated. This can be the EUI-64 derived IID
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of an interface, or some provable ID obtained
cryptographically.
6.2. Extended Duplicate Address Message Formats
The Duplicate Address Request (DAR) and the Duplicate Address
Confirmation (DAC) messages are defined in section 4.4 of [RFC6775].
Those messages follow a common base format, which enables information
from the ARO to be transported over multiple hops.
The Duplicate Address Messages are extended to adapt to the Extended
ARO format, as follows:
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 | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status | TID | Registration Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Owner Unique ID (EUI-64 or equivalent) +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Registered Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Duplicate Address Messages Format
Modified Message Fields
Code: The ICMP Code as defined in [RFC4443]. The ICMP Code
MUST be set to 1 with this specification. An odd
value of the ICMP Code indicates that the TID field
is present and obeys this specification.
TID: 1-byte integer; same definition and processing as the
TID in the EARO option as defined in Section 6.1.
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Owner Unique Identifier (OUI): 8 bytes; same definition and
processing as the OUI in the EARO option as defined
in Section 6.1.
6.3. New 6LoWPAN Capability Bits in the Capability Indication Option
This specification defines new capability bits for use in the 6CIO,
which was introduced by [RFC7400] for use in IPv6 ND RA messages.
Routers that support this specification SHOULD set the "E" flag and
6LN SHOULD favor 6LR routers that support this specification over
those that do not. Routers that are capable of acting as 6LR, 6LBR
and 6BBR SHOULD set the "L", "B" and "P" flags, respectively. In
particular, the function 6LR is often collocated with that of 6LBR.
Those flags are not mutually exclusive and if a router is capable of
performing multiple functions, it SHOULD set all the related flags.
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 | Length = 1 | Reserved |L|B|P|E|G|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: New capability Bits L, B, P, E in the 6CIO
Option Fields
Type: 36
L: Node is a 6LR, it can take registrations.
B: Node is a 6LBR.
P: Node is a 6BBR, proxying for nodes on this link.
E: This specification is supported and applied.
7. Backward Compatibility
7.1. Discovering the capabilities of an ND peer
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7.1.1. Using the "E" Flag in the 6CIO
If the 6CIO is used in an ND message and the sending node supports
this specification, then the "E" Flag MUST be set.
A router that supports this specification SHOULD indicate that with a
6CIO.
If the Registering Node (RN) receives a 6CIO in a Router
Advertisement message, then the setting of the "E" Flag indicates
whether or not this specification is supported.
7.1.2. Using the "T" Flag in the EARO
One alternate way for a 6LN to discover the router's capabilities to
first register a Link Local address, placing the same address in the
Source and Target Address fields of the NS message, and setting the
"T" Flag. The node may for instance register an address that is
based on EUI-64. For such address, DAD is not required and using the
SLLAO option in the NS is actually more consistent with existing ND
specifications such as the "Optimistic Duplicate Address Detection
(DAD) for IPv6" [RFC4429].
Once its first registration is complete, the node knows from the
setting of the "T" Flag in the response whether the router supports
this specification. If support is verified, the node may register
other addresses that it owns, or proxy-register addresses on behalf
some another node, indicating those addresses being registered in the
Target Address field of the NS messages, while using one of its own
previously registered addresses as source.
A node that supports this specification MUST always use an EARO as a
replacement to an ARO in its registration to a router. This is
harmless since the "T" flag and TID field are reserved in [RFC6775],
and are ignored by a legacy router. A router that supports this
specification answers an ARO with an ARO and answers an EARO with an
EARO.
This specification changes the behavior of the peers in a
registration flows. To enable backward compatibility, a 6LB that
registers to a 6LR that is not known to support this specification
MUST behave in a manner that is compatible with [RFC6775]. A 6LN can
achieve that by sending a NS(EARO) message with a Link-Local Address
used as both Source and Target Address, as described in Section 4.6.
Once the 6LR is known to support this specification, the 6LN MUST
obey this specification.
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7.2. Legacy 6LoWPAN Node
A legacy 6LN will use the Registered Address as source and will not
use an EARO option. An updated 6LR MUST accept that registration if
it is valid per [RFC6775], and it MUST manage the binding cache
accordingly. The updated 6LR MUST then use the legacy Duplicate
Address messages as specified in [RFC6775] to indicate to the 6LBR
that the TID is not present in the messages.
The main difference with [RFC6775] is that Duplicate Address exchange
for DAD is avoided for Link-Local addresses. In any case, the 6LR
SHOULD use an EARO in the reply, and may use any of the Status codes
defined in this specification.
7.3. Legacy 6LoWPAN Router
The first registration by an updated 6LN MUST be for a Link-Local
address, using that Link-Local address as source. A legacy 6LR will
not make a difference and treat that registration as if the 6LN was a
legacy node.
An updated 6LN will always use an EARO option in the registration NS
message, whereas a legacy 6LR will always reply with an ARO option in
the NA message. From that first registration, the updated 6LN can
determine whether or not the 6LR supports this specification.
After detecting a legacy 6LR, an updated 6LN may attempt to find an
alternate 6LR that is updated.
An updated 6LN SHOULD use an EARO in the request regardless of the
type of 6LR, legacy or updated, which implies that the "T" flag is
set.
If an updated 6LN moves from an updated 6LR to a legacy 6LR, the
legacy 6LR will send a legacy DAR message, which can not be compared
with an updated one for freshness.
Allowing legacy DAR messages to replace a state established by the
updated protocol in the 6LBR would be an attack vector and that
cannot be the default behavior.
But if legacy and updated 6LRs coexist temporarily in a network, then
it makes sense for an administrator to install a policy that allows
so, and the capability to install such a policy should be
configurable in a 6LBR though it is out of scope for this document.
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7.4. Legacy 6LoWPAN Border Router
With this specification, the Duplicate Address messages are extended
to transport the EARO information. Similarly to the NS/NA exchange,
updated 6LBR devices always use the Extended Duplicate Address
messages and all the associated behavior so they can amlways be
differentiated from legacy ones.
Note that a legacy 6LBR will accept and process an EDAR message as if
it was a legacy DAR, so legacy support of DAD is preserved.
8. Security Considerations
This specification extends [RFC6775], and the security section of
that draft also applies to this as well. In particular, it is
expected that the link layer is sufficiently protected to prevent a
rogue access, either by means of physical or IP security on the
Backbone Link and link layer cryptography on the LLN.
This specification also expects that the LLN MAC provides secure
unicast to/from the Backbone Router and secure Broadcast from the
Backbone Router in a way that prevents tempering with or replaying
the RA messages.
This specification recommends to using privacy techniques (see
Section 9, and protection against address theft such as provided by
"Address Protected Neighbor Discovery for Low-power and Lossy
Networks" [I-D.ietf-6lo-ap-nd], which guarantees the ownership of the
Registered Address using a cryptographic OUID.
The registration mechanism may be used by a rogue node to attack the
6LR or the 6LBR with a Denial-of-Service attack against the registry.
It may also happen that the registry of a 6LR or a 6LBR is saturated
and cannot take any more registration, which effectively denies the
requesting a node the capability to use a new address. In order to
alleviate those concerns, Section 4.7 provides a number of
recommendations that ensure that a stale registration is removed as
soon as possible from the 6LR and 6LBR. In particular, this
specification recommends that:
o A node that ceases to use an address SHOULD attempt to deregister
that address from all the 6LRs to which it is registered. See
Section 4.2 for the mechanism to avoid replay attacks and avoiding
the use of stale registration information.
o The Registration lifetimes SHOULD be individually configurable for
each address or group of addresses. The nodes SHOULD be
configured with a Registration Lifetime that reflects their
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expectation of how long they will use the address with the 6LR to
which it is registered. In particular, use cases that involve
mobility or rapid address changes SHOULD use lifetimes that are
larger yet of a same order as the duration of the expectation of
presence.
o The router (6LR or 6LBR) SHOULD be configurable so as to limit the
number of addresses that can be registered by a single node, as
identified at least by MAC address and preferably by security
credentials. When that maximum is reached, the router should use
a Least-Recently-Used (LRU) algorithm to clean up the addresses,
keeping at least one Link-Local address. The router SHOULD
attempt to keep one or more stable addresses if stability can be
determined, e.g. from the way the IID is formed or because they
are used over a much longer time span than other (privacy,
shorter-lived) addresses. Address lifetimes SHOULD be
individually configurable.
o In order to avoid denial of registration for the lack of
resources, administrators should take great care to deploy
adequate numbers of 6LRs to cover the needs of the nodes in their
range, so as to avoid a situation of starving nodes. It is
expected that the 6LBR that serves a LLN is a more capable node
then the average 6LR, but in a network condition where it may
become saturated, a particular deployment should distribute the
6LBR functionality, for instance by leveraging a high speed
Backbone and Backbone Routers to aggregate multiple LLNs into a
larger subnet.
The LLN nodes depend on the 6LBR and the 6BBR 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.
9. Privacy Considerations
As indicated in section Section 2, this protocol does not aim at
limiting the number of IPv6 addresses that a device can form. A host
should be able to form and register any address that is topologically
correct in the subnet(s) advertised by the 6LR/6LBR.
This specification does not mandate any particular way for forming
IPv6 addresses, but it discourages using EUI-64 for forming the
Interface ID in the Link-Local address because this method prevents
the usage of "SEcure Neighbor Discovery (SEND)" [RFC3971] and
"Cryptographically Generated Addresses (CGA)" [RFC3972], and that of
address privacy techniques.
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"Privacy Considerations for IPv6 Adaptation-Layer Mechanisms"
[RFC8065] explains why privacy is important and how to form such
addresses. All implementations and deployment must consider the
option of privacy addresses in their own environment. Also future
specifications involving 6LOWPAN Neighbor Discovery should consult
"Recommendation on Stable IPv6 Interface Identifiers" [RFC8064] for
default interface identifaction.
10. IANA Considerations
IANA is requested to make a number of changes under the "Internet
Control Message Protocol version 6 (ICMPv6) Parameters" registry, as
follows.
10.1. ARO Flags
IANA is requested to create a new subregistry for "ARO Flags". This
specification defines 8 positions, bit 0 to bit 7, and assigns bit 7
for the "T" flag in Section 6.1. The policy is "IETF Review" or
"IESG Approval" [RFC8126]. The initial content of the registry is as
shown in Table 2.
New subregistry for ARO Flags under the "Internet Control Message
Protocol version 6 (ICMPv6) [RFC4443] Parameters"
+-------------+--------------+-----------+
| ARO Status | Description | Document |
+-------------+--------------+-----------+
| 0..6 | Unassigned | |
| 7 | "T" Flag | This RFC |
+-------------+--------------+-----------+
Table 2: new ARO Flags
10.2. ICMP Codes
IANA is requested to create a new entry in the ICMPv6 "Code" Fields
subregistry of the Internet Control Message Protocol version 6
(ICMPv6) Parameters for the ICMP codes related to the ICMP type 157
and 158 Duplicate Address Request (shown in Table 3) and Confirmation
(shown in Table 4), respectively, as follows:
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New entries for ICMP types 157 DAR message
+-------+----------------------+------------+
| Code | Name | Reference |
+-------+----------------------+------------+
| 0 | Original DAR message | RFC 6775 |
| 1 | Extended DAR message | This RFC |
+-------+----------------------+------------+
Table 3: new ICMPv6 Code Fields
New entries for ICMP types 158 DAC message
+-------+----------------------+------------+
| Code | Name | Reference |
+-------+----------------------+------------+
| 0 | Original DAC message | RFC 6775 |
| 1 | Extended DAC message | This RFC |
+-------+----------------------+------------+
Table 4: new ICMPv6 Code Fields
10.3. New ARO Status values
IANA is requested to make additions to the Address Registration
Option Status Values Registry as follows:
Address Registration Option Status Values Registry
+-------------+-----------------------------------------+-----------+
| ARO Status | Description | Document |
+-------------+-----------------------------------------+-----------+
| 3 | Moved | This RFC |
| 4 | Removed | This RFC |
| 5 | Validation Requested | This RFC |
| 6 | Duplicate Source Address | This RFC |
| 7 | Invalid Source Address | This RFC |
| 8 | Registered Address topologically | This RFC |
| | incorrect | |
| 9 | 6LBR registry saturated | This RFC |
| 10 | Validation Failed | This RFC |
+-------------+-----------------------------------------+-----------+
Table 5: New ARO Status values
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10.4. New 6LoWPAN capability Bits
IANA is requested to make additions to the Subregistry for "6LoWPAN
capability Bits" as follows:
Subregistry for "6LoWPAN capability Bits" under the "Internet Control
Message Protocol version 6 (ICMPv6) Parameters"
+-----------------+----------------------+-----------+
| Capability Bit | Description | Document |
+-----------------+----------------------+-----------+
| 11 | 6LR capable (L bit) | This RFC |
| 12 | 6LBR capable (B bit) | This RFC |
| 13 | 6BBR capable (P bit) | This RFC |
| 14 | EARO support (E bit) | This RFC |
+-----------------+----------------------+-----------+
Table 6: New 6LoWPAN capability Bits
11. Acknowledgments
Kudos to Eric Levy-Abegnoli who designed the First Hop Security
infrastructure upon which the first backbone router was implemented.
Many thanks to Sedat Gormus, Rahul Jadhav and Lorenzo Colitti for
their various contributions and reviews. Also many thanks to Thomas
Watteyne for his early implementation of a 6LN that was instrumental
to the early tests of the 6LR, 6LBR and Backbone Router.
12. References
12.1. Normative References
[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>.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
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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>.
[RFC6282] Hui, J., Ed. and P. Thubert, "Compression Format for IPv6
Datagrams over IEEE 802.15.4-Based Networks", RFC 6282,
DOI 10.17487/RFC6282, September 2011,
<https://www.rfc-editor.org/info/rfc6282>.
[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>.
[RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
2014, <https://www.rfc-editor.org/info/rfc7400>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
12.2. Informative References
[I-D.chakrabarti-nordmark-6man-efficient-nd]
Chakrabarti, S., Nordmark, E., Thubert, P., and M.
Wasserman, "IPv6 Neighbor Discovery Optimizations for
Wired and Wireless Networks", draft-chakrabarti-nordmark-
6man-efficient-nd-07 (work in progress), February 2015.
[I-D.delcarpio-6lo-wlanah]
Vega, L., Robles, I., and R. Morabito, "IPv6 over
802.11ah", draft-delcarpio-6lo-wlanah-01 (work in
progress), October 2015.
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[I-D.ietf-6lo-ap-nd]
Sarikaya, B., Thubert, P., and M. Sethi, "Address
Protected Neighbor Discovery for Low-power and Lossy
Networks", draft-ietf-6lo-ap-nd-03 (work in progress),
September 2017.
[I-D.ietf-6lo-backbone-router]
Thubert, P., "IPv6 Backbone Router", draft-ietf-6lo-
backbone-router-04 (work in progress), July 2017.
[I-D.ietf-6lo-nfc]
Choi, Y., Hong, Y., Youn, J., Kim, D., and J. Choi,
"Transmission of IPv6 Packets over Near Field
Communication", draft-ietf-6lo-nfc-07 (work in progress),
June 2017.
[I-D.ietf-6tisch-architecture]
Thubert, P., "An Architecture for IPv6 over the TSCH mode
of IEEE 802.15.4", draft-ietf-6tisch-architecture-12 (work
in progress), August 2017.
[I-D.ietf-bier-architecture]
Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
S. Aldrin, "Multicast using Bit Index Explicit
Replication", draft-ietf-bier-architecture-08 (work in
progress), September 2017.
[I-D.ietf-ipv6-multilink-subnets]
Thaler, D. and C. Huitema, "Multi-link Subnet Support in
IPv6", draft-ietf-ipv6-multilink-subnets-00 (work in
progress), July 2002.
[I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks]
Popa, D. and J. Hui, "6LoPLC: Transmission of IPv6 Packets
over IEEE 1901.2 Narrowband Powerline Communication
Networks", draft-popa-6lo-6loplc-ipv6-over-
ieee19012-networks-00 (work in progress), March 2014.
[RFC1982] Elz, R. and R. Bush, "Serial Number Arithmetic", RFC 1982,
DOI 10.17487/RFC1982, August 1996,
<https://www.rfc-editor.org/info/rfc1982>.
[RFC3610] Whiting, D., Housley, R., and N. Ferguson, "Counter with
CBC-MAC (CCM)", RFC 3610, DOI 10.17487/RFC3610, September
2003, <https://www.rfc-editor.org/info/rfc3610>.
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[RFC3810] Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
DOI 10.17487/RFC3810, June 2004,
<https://www.rfc-editor.org/info/rfc3810>.
[RFC3971] Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971,
DOI 10.17487/RFC3971, March 2005,
<https://www.rfc-editor.org/info/rfc3971>.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, DOI 10.17487/RFC3972, March 2005,
<https://www.rfc-editor.org/info/rfc3972>.
[RFC4429] Moore, N., "Optimistic Duplicate Address Detection (DAD)
for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
<https://www.rfc-editor.org/info/rfc4429>.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, DOI 10.17487/RFC4919, August 2007,
<https://www.rfc-editor.org/info/rfc4919>.
[RFC4941] Narten, T., Draves, R., and S. Krishnan, "Privacy
Extensions for Stateless Address Autoconfiguration in
IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
<https://www.rfc-editor.org/info/rfc4941>.
[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>.
[RFC7217] Gont, F., "A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address
Autoconfiguration (SLAAC)", RFC 7217,
DOI 10.17487/RFC7217, April 2014,
<https://www.rfc-editor.org/info/rfc7217>.
[RFC7428] Brandt, A. and J. Buron, "Transmission of IPv6 Packets
over ITU-T G.9959 Networks", RFC 7428,
DOI 10.17487/RFC7428, February 2015,
<https://www.rfc-editor.org/info/rfc7428>.
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[RFC7668] Nieminen, J., Savolainen, T., Isomaki, M., Patil, B.,
Shelby, Z., and C. Gomez, "IPv6 over BLUETOOTH(R) Low
Energy", RFC 7668, DOI 10.17487/RFC7668, October 2015,
<https://www.rfc-editor.org/info/rfc7668>.
[RFC7934] Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
"Host Address Availability Recommendations", BCP 204,
RFC 7934, DOI 10.17487/RFC7934, July 2016,
<https://www.rfc-editor.org/info/rfc7934>.
[RFC8064] Gont, F., Cooper, A., Thaler, D., and W. Liu,
"Recommendation on Stable IPv6 Interface Identifiers",
RFC 8064, DOI 10.17487/RFC8064, February 2017,
<https://www.rfc-editor.org/info/rfc8064>.
[RFC8065] Thaler, D., "Privacy Considerations for IPv6 Adaptation-
Layer Mechanisms", RFC 8065, DOI 10.17487/RFC8065,
February 2017, <https://www.rfc-editor.org/info/rfc8065>.
[RFC8105] Mariager, P., Petersen, J., Ed., Shelby, Z., Van de Logt,
M., and D. Barthel, "Transmission of IPv6 Packets over
Digital Enhanced Cordless Telecommunications (DECT) Ultra
Low Energy (ULE)", RFC 8105, DOI 10.17487/RFC8105, May
2017, <https://www.rfc-editor.org/info/rfc8105>.
[RFC8163] Lynn, K., Ed., Martocci, J., Neilson, C., and S.
Donaldson, "Transmission of IPv6 over Master-Slave/Token-
Passing (MS/TP) Networks", RFC 8163, DOI 10.17487/RFC8163,
May 2017, <https://www.rfc-editor.org/info/rfc8163>.
12.3. External Informative References
[IEEEstd802154]
IEEE, "IEEE Standard for Low-Rate Wireless Networks",
IEEE Standard 802.15.4, DOI 10.1109/IEEE
P802.15.4-REVd/D01, June 2017,
<http://ieeexplore.ieee.org/document/7460875/>.
[Perlman83]
Perlman, R., "Fault-Tolerant Broadcast of Routing
Information", North-Holland Computer Networks 7: 395-405,
1983, <http://www.cs.illinois.edu/~pbg/courses/cs598fa09/
readings/p83.pdf>.
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Appendix A. Applicability and Requirements Served
This specification extends 6LoWPAN ND to sequence the registration
and serves the requirements expressed Appendix B.1 by enabling the
mobility of devices from one LLN to the next based on the
complementary work in the "IPv6 Backbone Router"
[I-D.ietf-6lo-backbone-router] specification.
In the context of the the TimeSlotted Channel Hopping (TSCH) mode of
IEEE Std. 802.15.4 [IEEEstd802154], the "6TiSCH architecture"
[I-D.ietf-6tisch-architecture] introduces how a 6LoWPAN ND host could
connect to the Internet via a RPL mesh Network, but this requires
additions to the 6LOWPAN ND protocol to support mobility and
reachability in a secured and manageable environment. This
specification details the new operations that are required to
implement the 6TiSCH architecture and serves the requirements listed
in Appendix B.2.
The term LLN is used loosely in this specification to cover multiple
types of WLANs and WPANs, including Low-Power Wi-Fi, BLUETOOTH(R) Low
Energy, IEEE Std.802.11AH and IEEE Std.802.15.4 wireless meshes, so
as to address the requirements discussed in Appendix B.3.
This specification can be used by any wireless node to associate at
Layer-3 with a 6BBR and register its IPv6 addresses to obtain routing
services including proxy-ND operations over the Backbone, effectively
providing a solution to the requirements expressed in Appendix B.4.
"Efficiency aware IPv6 Neighbor Discovery Optimizations"
[I-D.chakrabarti-nordmark-6man-efficient-nd] suggests that 6LoWPAN ND
[RFC6775] can be extended to other types of links beyond IEEE Std.
802.15.4 for which it was defined. The registration technique is
beneficial when the Link-Layer technique used to carry IPv6 multicast
packets is not sufficiently efficient in terms of delivery ratio or
energy consumption in the end devices, in particular to enable
energy-constrained sleeping nodes. The value of such extension is
especially apparent in the case of mobile wireless nodes, to reduce
the multicast operations that are related to IPv6 ND ([RFC4861],
[RFC4862]) and plague the wireless medium. This serves scalability
requirements listed in Appendix B.6.
Appendix B. Requirements
This section lists requirements that were discussed at 6lo for an
update to 6LoWPAN ND. This specification meets most of them, but
those listed in Appendix B.5 which are deferred to a different
specification such as [I-D.ietf-6lo-ap-nd], and those related to
multicast.
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B.1. Requirements Related to Mobility
Due to the unstable nature of LLN links, even in a LLN of immobile
nodes a 6LN may change its point of attachment to a 6LR, say 6LR-a,
and may not be able to notify 6LR-a. Consequently, 6LR-a may still
attract traffic that it cannot deliver any more. When links to a 6LR
change state, there is thus a need to identify stale states in a 6LR
and restore reachability in a timely fashion.
Req1.1: Upon a change of point of attachment, connectivity via a new
6LR MUST be restored timely without the need to de-register from the
previous 6LR.
Req1.2: For that purpose, the protocol MUST enable to differentiate
between multiple registrations from one 6LoWPAN Node and
registrations from different 6LoWPAN Nodes claiming the same address.
Req1.3: Stale states MUST be cleaned up in 6LRs.
Req1.4: A 6LoWPAN Node SHOULD also be capable to register its Address
to multiple 6LRs, and this, concurrently.
B.2. Requirements Related to Routing Protocols
The point of attachment of a 6LN may be a 6LR in an LLN mesh. IPv6
routing in a LLN can be based on RPL, which is the routing protocol
that was defined at the IETF for this particular purpose. Other
routing protocols than RPL are also considered by Standard Defining
Organizations (SDO) on the basis of the expected network
characteristics. It is required that a 6LoWPAN Node attached via ND
to a 6LR would need to participate in the selected routing protocol
to obtain reachability via the 6LR.
Next to the 6LBR unicast address registered by ND, other addresses
including multicast addresses are needed as well. For example a
routing protocol often uses a multicast address to register changes
to established paths. ND needs to register such a multicast address
to enable routing concurrently with discovery.
Multicast is needed for groups. Groups may be formed by device type
(e.g. routers, street lamps), location (Geography, RPL sub-tree), or
both.
The Bit Index Explicit Replication (BIER) Architecture
[I-D.ietf-bier-architecture] proposes an optimized technique to
enable multicast in a LLN with a very limited requirement for routing
state in the nodes.
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Related requirements are:
Req2.1: The ND registration method SHOULD be extended so that the 6LR
is able to advertise the Address of a 6LoWPAN Node over the selected
routing protocol and obtain reachability to that Address using the
selected routing protocol.
Req2.2: Considering RPL, the Address Registration Option that is used
in the ND registration SHOULD be extended to carry enough information
to generate a DAO message as specified in [RFC6550] section 6.4, in
particular the capability to compute a Path Sequence and, as an
option, a RPLInstanceID.
Req2.3: Multicast operations SHOULD be supported and optimized, for
instance using BIER or MPL. Whether ND is appropriate for the
registration to the 6BBR is to be defined, considering the additional
burden of supporting the Multicast Listener Discovery Version 2
[RFC3810] (MLDv2) for IPv6.
B.3. Requirements Related to the Variety of Low-Power Link types
6LoWPAN ND [RFC6775] was defined with a focus on IEEE Std.802.15.4
and in particular the capability to derive a unique Identifier from a
globally unique MAC-64 address. At this point, the 6lo Working Group
is extending the 6LoWPAN Header Compression (HC) [RFC6282] technique
to other link types ITU-T G.9959 [RFC7428], Master-Slave/Token-
Passing [RFC8163], DECT Ultra Low Energy [RFC8105], Near Field
Communication [I-D.ietf-6lo-nfc], IEEE Std. 802.11ah
[I-D.delcarpio-6lo-wlanah], as well as IEEE1901.2 Narrowband
Powerline Communication Networks
[I-D.popa-6lo-6loplc-ipv6-over-ieee19012-networks] and BLUETOOTH(R)
Low Energy [RFC7668].
Related requirements are:
Req3.1: The support of the registration mechanism SHOULD be extended
to more LLN links than IEEE Std.802.15.4, matching at least the LLN
links for which an "IPv6 over foo" specification exists, as well as
Low-Power Wi-Fi.
Req3.2: As part of this extension, a mechanism to compute a unique
Identifier should be provided, with the capability to form a Link-
Local Address that SHOULD be unique at least within the LLN connected
to a 6LBR discovered by ND in each node within the LLN.
Req3.3: The Address Registration Option used in the ND registration
SHOULD be extended to carry the relevant forms of unique Identifier.
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Req3.4: The Neighbour Discovery should specify the formation of a
site-local address that follows the security recommendations from
[RFC7217].
B.4. Requirements Related to Proxy Operations
Duty-cycled devices may not be able to answer themselves to a lookup
from a node that uses IPv6 ND on a Backbone and may need a proxy.
Additionally, the duty-cycled device may need to rely on the 6LBR to
perform registration to the 6BBR.
The ND registration method SHOULD defend the addresses of duty-cycled
devices that are sleeping most of the time and not capable to defend
their own Addresses.
Related requirements are:
Req4.1: The registration mechanism SHOULD enable a third party to
proxy register an Address on behalf of a 6LoWPAN node that may be
sleeping or located deeper in an LLN mesh.
Req4.2: The registration mechanism SHOULD be applicable to a duty-
cycled device regardless of the link type, and enable a 6BBR to
operate as a proxy to defend the Registered Addresses on its behalf.
Req4.3: The registration mechanism SHOULD enable long sleep
durations, in the order of multiple days to a month.
B.5. Requirements Related to Security
In order to guarantee the operations of the 6LoWPAN ND flows, the
spoofing of the 6LR, 6LBR and 6BBRs roles should be avoided. Once a
node successfully registers an address, 6LoWPAN ND should provide
energy-efficient means for the 6LBR to protect that ownership even
when the node that registered the address is sleeping.
In particular, the 6LR and the 6LBR then should be able to verify
whether a subsequent registration for a given address comes from the
original node.
In a LLN it makes sense to base security on layer-2 security. During
bootstrap of the LLN, nodes join the network after authorization by a
Joining Assistant (JA) or a Commissioning Tool (CT). After joining
nodes communicate with each other via secured links. The keys for
the layer-2 security are distributed by the JA/CT. The JA/CT can be
part of the LLN or be outside the LLN. In both cases it is needed
that packets are routed between JA/CT and the joining node.
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Related requirements are:
Req5.1: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
the 6LR, 6LBR and 6BBR to authenticate and authorize one another for
their respective roles, as well as with the 6LoWPAN Node for the role
of 6LR.
Req5.2: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
the 6LR and the 6LBR to validate new registration of authorized
nodes. Joining of unauthorized nodes MUST be impossible.
Req5.3: 6LoWPAN ND security mechanisms SHOULD lead to small packet
sizes. In particular, the NS, NA, DAR and DAC messages for a re-
registration flow SHOULD NOT exceed 80 octets so as to fit in a
secured IEEE Std.802.15.4 [IEEEstd802154] frame.
Req5.4: Recurrent 6LoWPAN ND security operations MUST NOT be
computationally intensive on the LoWPAN Node CPU. When a Key hash
calculation is employed, a mechanism lighter than SHA-1 SHOULD be
preferred.
Req5.5: The number of Keys that the 6LoWPAN Node needs to manipulate
SHOULD be minimized.
Req5.6: The 6LoWPAN ND security mechanisms SHOULD enable the
variation of CCM [RFC3610] called CCM* for use at both Layer 2 and
Layer 3, and SHOULD enable the reuse of security code that has to be
present on the device for upper layer security such as TLS.
Req5.7: Public key and signature sizes SHOULD be minimized while
maintaining adequate confidentiality and data origin authentication
for multiple types of applications with various degrees of
criticality.
Req5.8: Routing of packets should continue when links pass from the
unsecured to the secured state.
Req5.9: 6LoWPAN ND security mechanisms SHOULD provide a mechanism for
the 6LR and the 6LBR to validate whether a new registration for a
given address corresponds to the same 6LoWPAN Node that registered it
initially, and, if not, determine the rightful owner, and deny or
clean-up the registration that is duplicate.
B.6. Requirements Related to Scalability
Use cases from Automatic Meter Reading (AMR, collection tree
operations) and Advanced Metering Infrastructure (AMI, bi-directional
communication to the meters) indicate the needs for a large number of
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LLN nodes pertaining to a single RPL DODAG (e.g. 5000) and connected
to the 6LBR over a large number of LLN hops (e.g. 15).
Related requirements are:
Req6.1: The registration mechanism SHOULD enable a single 6LBR to
register multiple thousands of devices.
Req6.2: The timing of the registration operation should allow for a
large latency such as found in LLNs with ten and more hops.
Authors' Addresses
Pascal Thubert (editor)
Cisco Systems, Inc
Sophia Antipolis
FRANCE
Email: pthubert@cisco.com
Erik Nordmark
Santa Clara, CA
USA
Email: nordmark@sonic.net
Samita Chakrabarti
San Jose, CA
USA
Email: samitac.ietf@gmail.com
Charles E. Perkins
Futurewei
2330 Central Expressway
Santa Clara 95050
Unites States
Email: charliep@computer.org
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