Registration Extensions for 6LoWPAN Neighbor DiscoveryCisco Systems, IncBuilding D (Regus) 45 Allee des OrmesMougins - Sophia AntipolisFrance+33 4 97 23 26 34pthubert@cisco.comZededaSanta Clara, CAUnited States of Americanordmark@sonic.netVerizonSan Jose, CAUnited States of Americasamitac.ietf@gmail.comFuturewei2330 Central ExpresswaySanta Clara95050United States of Americacharliep@computer.org
Internet
6lo
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.
The scope of this draft is an IPv6 Low Power Network 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) to enable additional capabilities and
enhancements such as:
determining the freshest location in case of mobility (T-bit) Simplifying the registration flow for link-local addresses Support of a Leaf node in a route-over network Proxy registration in a route-over network Registration to a IPv6 ND proxy over a Backbone Link Clarification of support for privacy and temporary addresses
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 .
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)..
Other terms in use in LLNs are found in
Terminology for Constrained-Node Networks.
A glossary of some classical 6LoWPAN acronyms such as ARO, 6LN, 6LBR and 6CIO
is given in .
Readers are expected to be familiar with all the terms and concepts
that are discussed in
"Neighbor Discovery for IP version 6"
, "IPv6 Stateless Address Autoconfiguration"
, "Problem Statement and Requirements for
IPv6 over Low-Power Wireless Personal Area Network (6LoWPAN) Routing"
, "IPv6 over Low-Power
Wireless Personal Area Networks (6LoWPANs): Overview, Assumptions,
Problem Statement, and Goals" and "Neighbor Discovery Optimization
for Low-power and Lossy Networks".
as well as the following terminology:
An IPv6 transit link that interconnects two or more Backbone Routers.
It is expected to be of high 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.
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 this 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 the
same physical router may operate all three.
The aggregation of multiple LLNs as defined in
, interconnected
by a Backbone Link via Backbone Routers, and forming a single IPv6
MultiLink Subnet.
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.
The association between an IP address and a
MAC address, a port and/or other information about the node
that owns the IP address.
The node for which the registration is performed,
and which owns the fields in the Extended ARO option.
The node that performs the registration to the 6BBR, which may proxy
for the registered node.
An address owned by the Registered Node that was or is being registered.
Applied to a type of node or a type of message, this adjective indicates
a behavior that is strictly as specified by as
opposed to updated with this specification.
Qualifies a 6LN, a 6LR or a 6LBR that supports this specification.
The purpose of the Address Registration Option (ARO) in
is to facilitate duplicate address detection (DAD)
for hosts as well as to populate
Neighbor Cache Entries (NCEs) 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
by a 6LR or a 6LBR 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 ;
or a host using an address that 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
multiple addresses. Rather, the intention is to conform to
"Host Address Availability Recommendations".
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".
In IPv6 ND , a router needs enough storage
to hold NCEs for all the addresses to which it can currently forward
packets. 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 by the vendor and the dynamic use of associated resources SHOULD
be made available to the network operator, e.g. to a management console.
A network administrator MUST deploy updated 6LR/6LBRs to
support the number and type of devices in their network, based on the
number of IPv6 addresses that those devices require and their address
renewal rate and behavior.
This specification introduces the Extended Address Registration Option
(EARO) based on the ARO as defined
; 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 Link as illustrated in . Note that
this specification avoids the extended DAR flow for Link Local
Addresses in a Route-Over topology.
In order to support various types of link layers, it is RECOMMENDED to
allow multiple registrations, including for privacy / temporary
addresses. It is also RECOMMENDED to provide new mechanisms to help clean up
stale registration state as soon as possible.
Section 5 of specifies how a 6LN bootstraps an
interface and locates available 6LRs; a Registering Node SHOULD prefer
registering to a 6LR that is found to support this specification, as
discussed in , over an RFC6775-only one.
The Extended ARO (EARO) replaces the ARO and is backward compatible
with it. More details on backward compatibility can be found in
.
The semantics of the ARO are modified as follows:
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
(see ).
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.
The Unique ID in the EARO Option is not required to be a MAC
address
(see ).
This document specifies a new flag in the EARO option, the 'R' flag,
used by a 6LN, when registering, to indicate that this 6LN
is not a router and that it will not handle its own reachability.
If the 'R' flag is set, the registering node expects
that the 6LR ensures reachability for the registered address by means of
routing or proxying ND. A host SHOULD set the 'R' flag.
When not set, the 'R' flag indicates that the Registering Node is a
router, which for instance participates to a route-over routing
protocol such as RPL , and which will take
care of injecting the address over the routing protocol by itself.
A router SHOULD NOT set the 'R' flag.
The specification introduces a Transaction ID (TID) field in the
EARO (see ).
The TID MUST be provided by a node that supports this specification
and a new "T" flag MUST be set to indicate so.
Finally, this specification introduces new status
codes to help diagnose the cause of a registration failure
(see ).
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
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 6BBRs
in parallel, the same TID SHOULD be used. This enables the
6BBRs to determine that the registrations are the same, and
distinguish that situation from a movement (see section 4 of
and
below).
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 specification.
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 .
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
(), 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
. 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,
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). 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. When comparing two sequence counters, the following rules MUST
be applied: When a first sequence counter A is in the interval
[128..255] and a second sequence counter B is in [0..127]:
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. 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.
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.
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:
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
is used to determine the
relationships greater than, less than, and equal. 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.
If two sequence numbers are determined to be not comparable,
i.e. the results of the comparison are not defined, then a node
should give precedence to the sequence number that was most recently
incremented. Failing this, the node should select the sequence number
in order to minimize the resulting changes to its own state.
The Registration Unique ID (RUID) generalizes the EUI-64 field of the ARO in
. It is unique to a registration and enables to
identify the tentative to register a duplicate address, which is
characterized by a different RUID in the conflicting registrations
(more in )
With this specification, the Registration 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"
. In order to support the flows related to the proof of ownership,
this specification introduces new status codes "Validation Requested" and
"Validation Failed" in the EARO.
The Registering 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.
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 MUST expect
ND options after the main body, and MUST ignore them.
As for the EARO, the Extended Duplicate Address messages are backward
compatible with the RFC6775-only versions, and remarks concerning backwards
compatibility for the protocol between the 6LN and the 6LR apply
similarly between a 6LR and a 6LBR.
The Registering Node is the node that performs the registration to the
6BBR. As in , 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 the 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.
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
RFC6775-only 6LoWPAN ND .
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 ,
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 a Route-Over topology
for Link-Local addresses, by avoiding an exchange of Duplicate Address
messages between the 6LR and a 6LBR for those 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 at most 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.
When registering to a 6LR that conforms to 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 registered.
That Link-Local Address MUST be either an address that is already registered
to the 6LR, 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
.
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 a GUA as Source Address, in contrast to a node that
complies to . For non-Link-Local addresses,
the Duplicate Address
exchange MUST conform to , 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.
An ND message from the 6BBR over the Backbone Link 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; this is considered as an address duplication and
the first owner wins.
If the first owner is the registration (i.e. with an NS(EARO)) then the 6BBR
defends the address over the Backbone Link as prescribed by
. If the first owner is a node over the Backbone
Link (no ARO), then the 6BBR rejects the proxy-registration with a Status of
"Duplicate Address".
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 , 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 synchronized when they are distributed.
When its resource available for Neighbor Cache Entries are exhausted,
a 6LR cannot accept a new registration.
In that situation, the EARO is returned in a NA message with a Status
Code of "Neighbor Cache Full",
and the Registering Node may attempt to register to another 6LR.
If the registry in the 6LBR is saturated, then the LBR
cannot decide whether a new address is a duplicate.
In that case, the 6LBR replies to a EDAR message with an EDAC message
that carries a new Status Code indicating "6LBR Registry saturated"
.
Note: this code is used by 6LBRs instead of "Neighbor Cache Full"
when responding to a Duplicate Address message exchange and is
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, de-register 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 de-register 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
de-register 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 Code of "Moved"
SHOULD be used to clean up the state in the previous location.
For instance, as described in
,
the "Moved" status can be used by a 6BBR in an NA(EARO)
message to indicate that the ownership of the proxy state on the
Backbone Link was transferred to another 6BBR, as the consequence of a
movement of the device. If the receiver of the message has a state
corresponding to the related address, it SHOULD propagate
the status down the forwarding path to the Registered node
(e.g. reversing an existing RPL path as prescribed
in ) and whether it could or not do so,
the receiver MUST clean up the said state.
Upon receiving an NS(EARO) message with a Registration Lifetime of 0 and
determining that this EARO is the freshest for a given NCE
(see ), 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, 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 an EDAC message bearing a Status of "Success".
Otherwise, a Status Code of "Moved" is returned instead, and the existing
entry is maintained.
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 de-registered 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 silently removes its entry.
The "Generic Header Compression for IPv6
over 6LoWPANs" introduces the 6LoWPAN Capability
Indication Option (6CIO) to indicate a node's capabilities to its peers.
defines new flags for the 6CIO to signal
support for EARO, as well as the node's capability to act as a 6LR,
6LBR and 6BBR. specifies how the "E"
flag can be used to provide backward compatibility.
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.
This specification does not introduce new options, but it modifies
existing ones and updates the associated behaviors as specified in
the following subsections.
The Address Registration Option (ARO) is defined in section 4.1 of
.
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 LLN 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.
The EARO extends the ARO and is indicated by the "T" flag set.
The format of the EARO option is as follows:
Option Fields
33 8-bit unsigned integer. The length of the
option in units of 8 bytes. Always 2. 8-bit unsigned integer. Indicates the status of
a registration in the NA response. MUST be set to 0 in NS
messages. See below.ValueDescription 0..2 See .
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 failed 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 RUID 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 RUID
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 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 is passed on to the
Registering Node by the 6LR. 10 Validation Failed: The proof of ownership of the registered
address is not correct.
This field is unused. It MUST be initialized to zero by
the sender and MUST be ignored by the receiver.
If the 'R' flag is set, the registering node expects that the 6LR
ensures reachability for the registered address, e.g. by injecting
the address in a route-over routing protocol or proxying ND over a
Backbone Link.
One bit flag. Set if the next octet is used as a 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.
16-bit integer; expressed in minutes. 0 means that the
registration has ended and the associated state should
be removed.
A globally unique identifier for the node associated. This can
be the EUI-64 derived IID of an interface, or some provable ID
obtained cryptographically.
The Duplicate Address Request (DAR) and the Duplicate Address
Confirmation (DAC) messages are defined in section 4.4 of
. 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:
Modified Message Fields
The ICMP Code as defined in . 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.
1-byte integer; same definition and processing as the TID in
the EARO option as defined in .
8 bytes; same definition and processing as the RUID in the EARO
option as defined in .
This specification defines new capability bits for use in the 6CIO,
which was
introduced by for use in IPv6 ND RA messages.
Routers that support this specification MUST 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.
Option Fields
36 Node is a 6LR, it can take registrations. Node is a 6LBR. Node is a 6BBR, proxying for nodes on this link. This specification is supported and applied.
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 receives a 6CIO in a Router
Advertisement message, then the setting of the "E" Flag indicates
whether or not this specification is supported.
One alternate way for a 6LN to discover the router's capabilities is to
start by registering 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 an EUI-64. For such an 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 (ODAD) for IPv6".
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 of
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
, and are ignored by an RFC6775-only
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 flow. To enable backward compatibility, a 6LN that
registers to a 6LR that is not known to support this specification
MUST behave in a manner that is compatible with
. 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
. Once the 6LR is known to support this
specification, the 6LN MUST obey this specification.
an RFC6775-only 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
, and it MUST manage the
binding cache accordingly. The updated 6LR MUST then use the
RFC6775-only Duplicate Address messages as specified in
to
indicate to the 6LBR that the TID is not present in the messages.
The main difference from
is that the Duplicate Address
exchange for DAD is avoided for Link-Local addresses. In any case,
the 6LR SHOULD use an EARO in the reply, and can use any of the
Status codes defined in this specification.
The first registration by an updated 6LN MUST be for a Link-Local
address, using that Link-Local address as source. an RFC6775-only 6LR
will treat that registration as if the 6LN was an RFC6775-only node.
An updated 6LN will always use an EARO option in the registration
NS message, whereas an RFC6775-only 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 an RFC6775-only 6LR, an updated 6LN SHOULD attempt to find an
alternate 6LR that is updated for a reasonable time that depends on the
type of device and the expected deployment.
An updated 6LN SHOULD use an EARO in the request
regardless of the type of 6LR, RFC6775-only or updated, which implies
that the "T" flag is set.
If an updated 6LN moves from an updated 6LR to an RFC6775-only 6LR, the
RFC6775-only 6LR will send an RFC6775-only DAR message, which can not be
compared with an updated one for freshness.
Allowing RFC6775-only 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 RFC6775-only 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.
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 always be differentiated
from RFC6775-only ones.
Note that an RFC6775-only 6LBR will accept and process an EDAR message as if
it were an RFC6775-only DAR, so the support of DAD is preserved.
This specification extends , and
the security section of that standard 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 or Multicast from the
Backbone Router in a way that prevents tampering with or replaying
the RA messages.
This specification recommends using privacy techniques (see
), and protection against address theft such
as provided by "Address Protected
Neighbor Discovery for Low-power and Lossy Networks", which
guarantees the ownership of the Registered Address using a
cryptographic RUID.
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 registrations, which effectively denies
the requesting node the capability to use a new address.
In order to alleviate those concerns, 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:
A node that ceases to use an address SHOULD attempt to de-register
that address from all the 6LRs to which it is registered. See
for the mechanism to avoid replay attacks
and avoiding the use of stale registration information.
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 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.
The router (6LR or 6LBR) SHOULD be configurable so as to limit the
number of addresses that can be registered by a single node, but as a
protective measure only. A node may be identified by MAC address,
but a stringer identification (e.g., by security credentials) is
RECOMMENDED.
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., because they are used over a much longer time
span than other (privacy, shorter-lived) addresses. Address lifetimes
SHOULD be individually configurable.
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 Link 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. This trust model could be
at a minimum based on a Layer-2 access control, or could provide role
validation as well (see Req5.1 in ).
As indicated in , this protocol does not
aim at limiting the number of IPv6 addresses that a device can form and
if placed, a limit should be a protective measure only, that is high enough
not to interfere with the normal behavior of devices in the network.
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)" and
"Cryptographically Generated Addresses (CGA)"
, and that of address privacy techniques.
"Privacy Considerations for IPv6 Adaptation-Layer Mechanisms"
explains why privacy is important and how to form privacy-aware addresses.
All implementations and deployment must consider the option of privacy
addresses in their own environment.
The IPv6 address of the 6LN in the IPv6 header can be compressed
statelessly when the Interface Identifier in the IPv6 address can be derived
from the Lower Layer address. When it is not critical to benefit from that
compression, e.g. the address can be compressed statefully, or it is rarely
used and/or it is used only over one hop, then privacy concerns
should be considered. In particular, new implementations should follow
the IETF
"Recommendation on Stable IPv6 Interface Identifiers" recommends the use of
"A Method for Generating Semantically Opaque
Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)"
for generating Interface Identifiers to be used in SLAAC.
Note to RFC Editor: please replace "This RFC" throughout this document by the RFC number for this specification once it is attributed.
IANA is requested to make a number of changes under the
"Internet Control Message Protocol version 6 (ICMPv6) Parameters"
registry, as follows.
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 . The policy is
"IETF Review" or "IESG Approval" .
The initial
content of the registry is as shown in .
New subregistry for ARO Flags under the
"Internet Control Message Protocol version 6 (ICMPv6)
Parameters" ARO Status Description Document 0..6 Unassigned 7 "T" FlagThis RFC
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 ) and Confirmation
(shown in ), respectively, as follows:
New entries for ICMP types 157 DAR message Code Name Reference 0Original DAR messageRFC 67751Extended DAR messageThis RFCNew entries for ICMP types 158 DAC message Code Name Reference 0Original DAC messageRFC 67751Extended DAC messageThis RFC 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 3MovedThis RFC4RemovedThis RFC5Validation RequestedThis RFC6Duplicate Source AddressThis RFC7Invalid Source AddressThis RFC8Registered Address topologically incorrectThis RFC96LBR registry saturatedThis RFC10Validation FailedThis RFC
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 116LR capable (L bit)This RFC126LBR capable (B bit)This RFC136BBR capable (P bit)This RFC14EARO support (E bit)This RFC
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, Tim Chown, Juergen Schoenwaelder,
Chris Lonvick
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.
IEEE Standard for Low-Rate Wireless NetworksIEEE Fault-Tolerant Broadcast of Routing
InformationDigital Equipment Corp.
This specification extends 6LoWPAN ND to provide a sequence number to the
registration and
serves the requirements expressed in by enabling the
mobility of devices from one LLN to the next based on the complementary
work in the
"IPv6 Backbone Router"
specification.
In the context of the TimeSlotted Channel Hopping (TSCH) mode of
IEEE Std. 802.15.4, the
"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 .
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
.
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 a Backbone Link, effectively
providing a solution to the requirements expressed in
.
This specification is extended by
"Address Protected Neighbor Discovery for Low-power and Lossy Networks"
to providing a solution to some of the security-related requirements
expressed in .
"Efficiency aware IPv6 Neighbor Discovery Optimizations"
suggests that 6LoWPAN ND 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 (, ) and affect the
operation of the wireless medium
.
This serves the scalability requirements listed in .
This section lists requirements that were discussed at 6lo for an
update to 6LoWPAN ND. How those requirements are matched with
existing specifications at the time of this writing is shown in
.
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 in a timely fashion without the need to
de-register from the previous 6LR.
Req1.2: For that purpose, the protocol MUST enable differentiating
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 able to register its
Address concurrently to multiple 6LRs.
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 are also considered by Standard
Development 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
proposes an optimized technique to enable multicast in a LLN
with a very limited requirement for routing state in the nodes.
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
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 (MLDv2) for IPv6.
6LoWPAN ND 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 EUI-64 address. At this
point, the 6lo Working Group is extending the
6LoWPAN Header Compression (HC)
technique to other link types
ITU-T G.9959,
Master-Slave/Token-Passing,
DECT Ultra Low Energy,
Near Field Communication,
IEEE Std. 802.11ah,
as well as
IEEE1901.2 Narrowband Powerline Communication Networks
and BLUETOOTH(R) Low Energy.
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.
Req3.4: The Neighbor Discovery should specify the formation of a
site-local address that follows the security recommendations from
.
Duty-cycled devices may not be able to answer themselves to a
lookup from a node that uses IPv6 ND on a Backbone Link 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.
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 an 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.
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 prevented.
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 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 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.
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 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.
Section 3.8 of
"Architectural Principles of the Internet"
recommends to : "avoid options and parameters whenever possible.
Any options and parameters should be configured or negotiated
dynamically rather than manually".
This is especially true in LLNs where the number of devices may be large
and manual configuration is infeasible.
Capabilities for a dynamic configuration of LLN devices can also be
constrained by the network and power limitation.
A Network Administrator should be able to validate that the network
is operating within capacity, and that in particular a 6LBR does not
get overloaded with an excessive amount of registration, so he can take
actions such as adding a Backbone Link with additional 6LBRs and 6BBRs
to his network.
Related requirements are:
Req7.1: A management model SHOULD be provided providing access to the
6LBR and its capacity. It is recommended that the 6LBR be reachable over
a non-LLN link.
Req7.2: A management model SHOULD be provided providing access to the
6LR and its capacity to host additional NCE. This management model
SHOULD avoid polling individual 6LRs n a way that could disrupt the
operation of the LLN.
Req7.3: information on successful and failed registration SHOULD be
provided, including information such as the RUID of the 6LN, the
Registered Address, the Address of the 6LR and the duration of the
registration flow.
Req7.4: In case of a failed registration, information on the failure
including the identification of the node that rejected the registration
and the status in the EARO SHOULD be provided
I-drafts/RFCs addressing requirements Requirement Document Req1.1Req1.2Req1.3Req1.4This RFCReq2.1This RFCReq2.2This RFCReq2.3Req3.1Technology DependantReq3.2Technology DependantReq3.3Technology DependantReq3.4Technology DependantReq4.1This RFCReq4.2This RFCReq4.3Req5.1Req5.2Req5.3Req5.4Req5.5Req5.6Req5.7Req5.8Req5.9Req6.1This RFCReq6.2This RFCReq7.1Req7.2Req7.3Req7.4 This document often uses the following acronyms:
6LoWPAN Backbone Router (proxy for the registration) 6LoWPAN Border Router (authoritative on DAD) 6LoWPAN Node 6LoWPAN Router (relay to the registration process) Capability Indication Option (Extended) Address Registration Option Duplicate Address Detection Low Power Lossy Network (a typical IoT network) Neighbor Advertisement Neighbor Cache Entry Neighbor Discovery Neighbor Discovery Protocol Neighbor Solicitation Registration Unique ID TimeSlotted Channel Hopping Transaction ID (a sequence counter in the EARO)