6LoWPAN Routing HeaderCisco SystemsBuilding D - Regus45 Allee des OrmesBP1200MOUGINS - Sophia Antipolis06254FRANCE+33 4 97 23 26 34pthubert@cisco.comUniversitaet Bremen TZIPostfach 330440BremenD-28359Germany+49-421-218-63921cabo@tzi.orgInstitut MINES TELECOM; TELECOM Bretagne2 rue de la ChataigneraieCS 17607Cesson-Sevigne Cedex35576FranceLaurent.Toutain@telecom-bretagne.euARM Ltd.110 Fulbourn RoadCambridgeCB1 9NJUKrobert.cragie@gridmerge.com
Internet
rollThis specification introduces a new 6LoWPAN dispatch type for use in
6LoWPAN Route-Over topologies, that initially covers the needs of RPL (RFC6550)
data packets compression. Using this dispatch type,
this specification defines a method to compress RPL Option (RFC6553) information and Routing Header
type 3 (RFC6554), an efficient IP-in-IP technique and is extensible for more applications.The design of Low Power and Lossy Networks (LLNs) is generally
focused on saving
energy, a very constrained resource in most cases. The other
constraints, such as the memory capacity and the duty cycling of the LLN
devices, derive from that primary concern. Energy is often available
from primary batteries that are expected to last for years, or is scavenged from the
environment in very limited quantities. Any protocol that is intended for
use in LLNs must be designed with the primary concern of saving energy as
a strict requirement.Controlling the amount of data transmission is one possible venue to save
energy. In a number of LLN standards, the frame size is limited to much
smaller values than the IPv6 maximum transmission unit (MTU) of 1280 bytes.
In particular, an LLN that relies on the classical Physical Layer (PHY)
of IEEE 802.15.4 is limited to 127 bytes
per frame. The need to compress IPv6 packets over IEEE 802.15.4 led to
the 6LoWPAN Header Compression work (6LoWPAN-HC).Innovative Route-over techniques have been and are still being developed for
routing inside a LLN. In a general fashion, such techniques require additional
information in the packet to provide loop prevention and to indicate
information such as flow identification,
source routing information, etc.For reasons such as security and the capability to send ICMP errors back to the
source, an original packet must not be tampered with, and any information that
must be inserted in or removed from an IPv6 packet must be placed in an extra
IP-in-IP encapsulation.
This is the case when the additional routing information is inserted by a router
on the path of a packet, for instance a mesh root, as opposed to the source node.
This is also the case when some routing information must be removed from a
packet that flows outside the LLN.
When to use RFC 6553, 6554 and IPv6-in-IPv6
details different cases where RFC 6553, RFC 6554 and IPv6-in-IPv6 encapsulation
is required to set the bases to help defining the compression of RPL routing
information in LLN environments.When using the outer IP header of an IP-in-IP encapsulation may be
compressed down to 2 octets in stateless compression and down to 3 octets
in stateful compression when context information must be added.The Stateless Compression of an IPv6 addresses can only happen if the IPv6 address
can de deduced from the MAC addresses, meaning that the IP end point is also the
MAC-layer endpoint. This is generally not the case in a RPL network which is
generally a multi-hop route-over (i.e., operated at Layer-3) network.
A better compression,
which does not involve variable compressions depending on the hop in the mesh,
can be achieved based on the fact that the outer encapsulation is usually between
the source (or destination) of the inner packet and the root.
Also, the inner IP header can only be compressed by if all the fields
preceding it are also compressed. This specification makes the inner IP header
the first header to be compressed by , and keeps the inner packet
encoded the same way whether it is encapsulated or not, thus preserving existing
implementations.As an example, the Routing Protocol for Low Power and Lossy Networks
(RPL) is designed to optimize the routing operations in constrained LLNs.
As part of this optimization, RPL requires the addition of RPL Packet Information
(RPI) in every packet, as defined in Section 11.2 of .The RPL Option for Carrying RPL Information in Data-Plane Datagrams
specification indicates how the RPI can be placed in a RPL Option (RPL-OPT) that
is placed in an IPv6 Hop-by-Hop header.This representation demands a total of 8 bytes, while in most cases the actual
RPI payload requires only 19 bits. Since the Hop-by-Hop header must not
flow outside of the RPL domain, it must be inserted in packets
entering the domain and be removed from packets that leave the domain.
In both cases, this operation implies an IP-in-IP encapsulation.Additionally, in the case of the Non-Storing Mode of Operation (MOP), RPL
requires a Source Routing Header (SRH) in all packets that are routed down a RPL
graph. for that purpose, the [IPv6 Routing Header for Source Routes with RPL]
(#RFC6554) specification defines the type 3 Routing Header for IPv6 (RH3).With Non-Storing RPL, even if the source is a node in the same LLN, the packet must first
reach up the graph to the root so that the root can insert the SRH to go down
the graph. In any fashion, whether the packet was originated in a node
in the LLN or outside the LLN, and regardless of whether the packet stays within
the LLN or not, as long as the source of the packet is not the root itself,
the source-routing operation also implies an IP-in-IP encapsulation at the root
in order to insert the SRH.6TiSCH specifies the
operation of IPv6 over the TimeSlotted Channel Hopping
(TSCH) mode of
operation of IEEE 802.15.4. The architecture requires the use of both RPL and
the 6lo adaptation layer over IEEE 802.15.4.
Because it inherits the constraints on frame size
from the MAC layer, 6TiSCH cannot afford to allocate 8 bytes per packet
on the RPI.
Hence the requirement for 6LoWPAN header compression of the RPI.An extensible compression technique is required that simplifies IP-in-IP
encapsulation when it is needed, and optimally compresses existing routing
artifacts found in RPL LLNs.This specification extends the 6lo adaptation layer framework
(,) so
as to carry routing information for route-over networks based on RPL.
The specification includes the formats necessary for RPL and is extensible
for additional formats.The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”,
“SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “NOT RECOMMENDED”,
“MAY”,
and “OPTIONAL” in this document are to be interpreted as
described in .The Terminology used in this document is consistent with and incorporates that
described in `Terminology in Low power And Lossy Networks’ and
.The terms Route-over and Mesh-under are defined in .Other terms in use in LLNs are found in .The term “byte” is used in its now customary sense as a synonym for
“octet”.The 6LoWPAN Paging Dispatch specification extends
the 6lo adaptation layer framework (, )
by introducing a concept of “context” in the 6LoWPAN parser,
a context being identified by a Page number. The specification defines 16 Pages.This draft operates within Page 1, which is indicated by a
Dispatch Value of binary 11110001.This specification introduces a new 6LoWPAN Routing Header (6LoRH)
to carry IPv6 routing information. The 6LoRH may contain source routing
information such as a compressed form of SRH, as well as other sorts of
routing information such as the RPI and IP-in-IP encapsulation.The 6LoRH is expressed in a 6loWPAN packet as a Type-Length-Value (TLV) field,
which is extensible for future use.This specification uses the bit pattern 10xxxxxx
in Page 1 for the new 6LoRH Dispatch.
describes how RPL artifacts in data packets can be compressed
as 6LoRH headers.In a zone of a packet where Page 1 is active (i.e., once a Page 1 Paging Dispatch
is parsed and no subsequent Paging Dispatch has been parsed,
the parsing of the packet MUST follow this specification if the 6LoRH Bit Pattern
is found.With this specification, the 6LoRH Dispatch is only defined in Page 1, so it MUST be
placed in the packet in a zone where the Page 1 context is active.Because a 6LoRH header requires a Page 1 context, it MUST always be placed
after any Fragmentation Header and/or Mesh Header .A 6LoRH header MUST always be placed before the LOWPAN_IPHC as defined in
6LoWPAN Header Compression . It is designed in such a fashion that
placing or removing a header that is encoded with 6LoRH does not modify the part
of the packet that is encoded with LoWPAN_IPHC, whether there is an IP-in-IP
encapsulation or not. For instance, the final destination of the packet is
always the one in the LOWPAN_IPHC whether there is a Routing Header or not.IPv6 defines chains of headers that are introduced by an IPv6 header
and terminated by either another IPv6 header (IP-in-IP) or an Upper Layer Protocol
ULP) header. When an outer header is stripped from the packet, the whole chain
goes with it. When one or more header(s) are inserted by an intermediate router,
that router normally chains the headers and encapsulates the result in IP-in-IP.With this specification, the chains of headers MUST be compressed in the same
order as they appear in the uncompressed form of the packet. This means that if
there is more than one nested IP-in-IP encapsulations, the first IP-in-IP
encapsulation, with all its chain of headers, is encoded first in the compressed
form.In the compressed form of a packet that has SRH or HbH headers after the inner
IPv6 header (e.g. if there is no IP-in-IP encapsulation), these headers are
placed in the 6LoRH form before the 6LOWPAN-IPHC that represents the IPv6 header
. If this packet gets encapsulated and some other SRH or
HbH headers are added as part of the encapsulation, placing the 6LoRH headers
next to one another may present an ambiguity on which header belong to which
chain in the uncompressed form.In order to disambiguate the headers that follow the inner IPv6 header in the
uncompressed form from the headers that follow the outer IP-in-IP header, it is
REQUIRED that the compressed IP-in-IP header is placed last in the encoded chain.
This means that the 6LoRH headers that are found after the last compressed
IP-in-IP header are to be inserted after the IPv6 header that is encoded with
the 6LOWPAN-IPHC when decompressing the packet.With regards to the relative placement of the SRH and the RPI in the compressed
form, it is a design point for this specification that the SRH entries are
consumed as the packet progresses down the LLN .
In order to make this operation simpler in the compressed form, it is REQUIRED
that the in the compressed form, the addresses along the source route path are
encoded in the order of the path, and that the compressed SRH are placed before
the compressed RPI.The 6LoRH usesthe Dispatch Value Bit Pattern of 10xxxxxx in Page 1.The Dispatch Value Bit Pattern is split in two forms of 6LoRH:Elective (6LoRHE) that may skipped if not understoodCritical (6LoRHC) that may not be ignoredThe 6LoRHE uses the Dispatch Value Bit Pattern of 101xxxxx.
A 6LoRHE may be ignored and skipped in parsing.
If it is ignored, the 6LoRHE is forwarded with no change inside the LLN.
Length of the 6LoRHE expressed in bytes, excluding the first 2 bytes.
This enables a node to skip a 6LoRHE header that it does not support and/or
cannot parse, for instance if the Type is not recognized.
Type of the 6LoRHEThe 6LoRHC uses the Dispatch Value Bit Pattern of 100xxxxx.A node which does not support the 6LoRHC Type MUST silently discard the packet.Note:
The situation where a node receives a message with a Critical 6LoWPAN Routing
Header that it does not understand is a critical administrative error whereby the
wrong device is placed in a network. It makes no sense to overburden the
constrained device with code that would send an ICMP error to the source.
Rather, it is expected that the device will raise some management alert indicating
that it cannot operate in this network for that reason. As a result,
there is no provision for the exchange of error messages for this situation, so
it should be avoided by judicious use of administrative control
and/or capability indications by the device manufacturer.
Type Specific Extension. The meaning depends on the Type, which must be known in all of the nodes. The interpretation of the TSE depends on the Type field that follows. For instance, it may be used to transport control bits, the number of elements in an array, or the length of the remainder of the 6LoRHC expressed in a unit other than bytes.
Type of the 6LoRHCThe general technique used in this draft to compress an address is first to determine
a reference that as a long prefix match with this address, and then elide that matching
piece. In order to reconstruct the compress address, the receiving node will perform
the process of coalescence described in section .One possible reference is the root of the RPL DODAG that is being traversed. It
is used by 6LoRH as the reference to compress an outer IP header, in case of an
IP-in-IP encapsulation. If the root is the source of the packet, this
technique allows to fully elide the source address in the compressed form of the IP
header. If the root is not the encapsulator, then the encapsulator address may still be
compressed using the root as reference. How the address of the root is determined is
discussed in .Once the address of the source of the packet is determined, it becomes the reference
for the compression of the addresses that are located in compressed SRH headers that
are present inside the IP-in-IP encapsulation in the uncompressed form.An IPv6 compressed address is coalesced with a reference address by overriding
the N rightmost bytes of the reference address with the compressed address,
where N is the length of the compressed address, as indicated by the Type of the
SRH-6LoRH header in .The reference address MAY be a compressed address as well, in which case
it MUST be compressed in a form that is of an equal or greater length than
the address that is being coalesced.A compressed address is expanded by coalescing it with a reference address. In
the particular case of a Type 4 SRH-6LoRH, the address is expressed in full and
the coalescence is a complete override as illustrated in .Stateful Address compression requires that some state is installed in the devices
to store the compression information that is elided from the packet.
That state is stored in an abstract context table and some form of index is found
in the packet to obtain the compression information from the context table.With , the state is provided to the stack by the 6LoWPAN Neighbor
Discovery Protocol (NDP) . NDP exchanges the context through 6LoWPAN
Context Option in Router Advertisement (RA) messages. In the compressed form of
the packet, the context can be signaled in a Context Identifier Extension.With this specification, the compression information is provided to the stack by
RPL, and RPL exchanges it through the DODAGID field in the DAG Information Object
(DIO) messages, as described in more details below. In the compressed form of
the packet, the context can be signaled in by the RPLInstanceID in the RPI.With RPL , the address of the DODAG root is known from the DODAGID
field
of the DIO messages. For a Global Instance, the RPLInstanceID that is present in
the RPI is enough information to identify the DODAG that this node participates
to and its associated root. But for a Local Instance, the address of the root
MUST be explicit, either in some device configuration or signaled in the packet,
as the source or the destination address, respectively.When implicit, the address of the DODAG root MUST be determined as follows:If the whole network is a single DODAG then the root can be well-known and does
not need to be signaled in the packets. But since RPL does not expose that
property, it can only be known by a configuration applied to all nodes.Else, the router that encapsulates the packet and compresses it with this
specification MUST also place an RPI in the packet as prescribed by
to enable the identification of the DODAG. The RPI must be present even in the
case when the router also places an SRH header in the packet.It is expected that the RPL implementation maintains an abstract context table,
indexed by Global RPLInstanceID, that provides the address of the root of the
DODAG that this nodes participates to for that particular RPL Instance.The Source Routing Header 6LoRH (SRH-6LoRH) header
is a Critical 6LoWPAN Routing Header that
provides a compressed form for the SRH, as defined
in for use by RPL routers. Routers that need to
forward a packet with a SRH-6LoRH are expected to be RPL routers and are expected
to support this specification. If a non-RPL router receives a packet with
a SRH-6LoRH, this means that there was a routing error and the packet should be
dropped so the Type cannot be ignored.The 6LoRH Type indicates the compression level used in a given SRH-6LoRH header.One or more 6LoRH header(s) MAY be placed in a 6LoWPAN packet.It results that all addresses in a given SRH-6LoRH header MUST be compressed in
an identical fashion, down to using the identical number of bytes per address.
In order to get different degrees of compression, multiple consecutive SRH-6LoRH
headers MUST be used.Type 0 means that the address is compressed down to one byte, whereas Type 4
means that the address is provided in full in the SRH-6LoRH with no compression.
The complete list of Types of SRH-6LoRH and the corresponding compression level
are provided in :In the case of a SRH-6LoRH header, the TSE field is used as a Size,
which encodes the number of hops minus 1; so a Size of 0 means one
hop, and the maximum that can be encoded is 32 hops. (If more than
32 hops need to be expressed, a sequence of SRH-6LoRH elements can be
employed.) It results that the Length in bytes of a SRH-6LoRH header is:2 + Length_of_compressed_IPv6_address * (Size + 1)In the non-compressed form, when the root generates or forwards a packet in
non-Storing Mode, it needs to include a Source Routing Header
to signal a strict source-route path to a final destination down the DODAG.All the hops along the path, but the first one, are encoded in order in the SRH.
The last entry in the SRH is the final destination and the destination in the
IPv6 header is the first hop along the source-route path. The intermediate hops
perform a swap and the Segment-Left field indicates the active entry in the
Routing Header .The current destination of the packet, which is the
termination of the current segment, is indicated at all times by the destination
address of the IPv6 header.The handling of the SRH-6LoRH is different: there is no swap, and a forwarding
router that corresponds to the first entry in the first SRH-6LoRH upon reception
of a packet effectively consumes that entry when forwarding. This means that the
size of a compressed source-routed packet decreases as the packet progresses
along its path and that the routing information is lost along the way. This also
means that an SRH encoded with 6LoRH is not recoverable and cannot be protected.When compressed with this specification, all the remaining hops MUST be encoded
in order in one or more consecutive SRH-6LoRH headers. Whether or not there
is a SRH-6LoRH header present, the address of the final destination is indicated
in the LoWPAN_IPHC at all times along the path. Examples of this are provided in
.The current destination (termination of the current segment) for a compressed
source-routed packet is indicated in the first entry of the first SRH-6LoRH.
In strict source-routing, that entry MUST match an address of the router that
receives the packet.The last entry in the last SRH-6LoRH is the last router on the way to the final
destination in the LLN. This router can be the final destination if it is found
desirable to carry a whole IP-in-IP encapsulation all the way. Else, it is the
RPL parent of the final destination, or a router acting at 6LR for
the destination host, and advertising the host as an external route to RPL.If the SRH-6LoRH header is contained in an IP-in-IP encapsulation, the last router
removes the whole chain of headers. Otherwise, it removes the SRH-6LoRH header
only.6LoWPAN ND is designed to support more than one IPv6 address
per node and per Interface Identifier (IID), an IID being typically derived
from a MAC address to optimize the LOWPAN-IPHC compression.Link local addresses are compressed with stateless address compression (S/DAC=0).
The other addresses are derived from different prefixes and they can be compressed
with stateful address compression based on a context (S/DAC=1).But stateless compression is only defined for the specific link-local prefix as
opposed to the prefix in an encapsulating header. And with stateful compression,
the compression reference is found in a context, as opposed to an encapsulating
header.It results that in the case of an IP-in-IP encapsulation, it is possible to
compress an inner source (respectively destination) IP address in a LOWPAN_IPHC
based on the encapsulating IP header only if stateful (context-based) compression
is used. The compression will operate only if the IID in the source (respectively
the destination) IP address in the outer and inner headers match, which usually
means that they refer to the same node . This is encoded as S/DAC = 1 and S/AM=11.
It must be noted that the outer destination address that is used to compress the
inner destination address is the last entry in the last SRH-6LoRH header.In order to save energy and to optimize the chances of transmission success on
lossy media, it is a design point for this specification that the entries in the
SRH that have been used are removed from the packet. This creates a discrepancy
from the art of IPv6 where Routing Header are mutable but recoverable.With this specification, the packet can be expanded at any hop into a valid IPv6
packet, including a SRH, and compressed back. But the packet as decompressed
along the way will not carry all the consumed addresses that packet would have
if it had been forwarded in the uncompressed form.It is noted that:The value of keeping the whole RH in an IPv6 header is for the receiver to
reverse it to use the symmetrical path on the way back.It is generally not a good idea to reverse a routing header. The RH may have
been used to stay away from the shortest path for some reason that is only
valid on the way in (segment routing).There is no use of reversing a RH in the present RPL specifications.P2P RPL reverses a path that was learned reactively, as a part of the protocol
operation, which is probably a cleaner way than a reversed echo on the data
path.Reversing a header is discouraged by for RH0 unless it is
authenticated, which requires an Authentication Header (AH). There is no
definition of an AH operation for SRH, and there is no indication that the
need exists in LLNs.It is noted that AH does not protect the RH on the way. AH is a validation at
the receiver with the sole value of enabling the receiver to reversing it.A RPL domain is usually protected by L2 security and that secures both RPL
itself and the RH in the packets, at every hop. This is a better security than
that provided by AH.In summary, the benefit of saving energy and lowering the chances of loss by
sending smaller frames over the LLN are seen as overwhelming compared to the
value of possibly reversing the header.In order to optimize the compression of IP addresses present in the SRH headers,
this specification requires that the 6LoWPAN layer identifies an address that is
used as reference for the compression.With this specification, the Compression Reference for the first address found
in an SRH header is the source of the IPv6 packet, and then the reference for
each subsequent entry is the address of its predecessor once it is uncompressed.With RPL , an SRH header may only be present in Non-Storing mode, and
it may only be placed in the packet by the root of the DODAG, which must be the
source of the resulting IPv6 packet . In this case, the address used
as Compression Reference is that the address of the root, and it can be implicit
when the address of the root is.The Compression Reference MUST be determined as follows:The reference address may be obtained by configuration. The configuration may
indicate either the address in full, or the identifier of a 6LoWPAN Context that
carries the address , for instance one of the 16 Context Identifiers
used in LOWPAN-IPHC .Else, and if there is no IP-in-IP encapsulation, the source address in the IPv6
header that is compressed with LOWPAN-IPHC is the reference for the compression.Else, and if the IP-in-IP compression specified in this document is used and the
Encapsulator Address is provided, then the Encapsulator Address is the reference.Upon reception, the router checks whether the address in the first entry of the
first SRH-6LoRH one of its own addresses. In that case, router MUST consume that
entry before forwarding, which is an action of popping from a stack, where the
stack is effectively the sequence of entries in consecutive SRH-6LoRH headers.Popping an entry of an SRH-6LoRH header is a recursive action performed as
follows:If the Size of the SRH-6LoRH header is 1 or more, indicating that there
are at least 2 entries in the header, the router removes the first entry and
decrements the Size (by 1).Else (meaning that this is the last entry in the SRH-6LoRH header), and
if there is no next SRH-6LoRH header after this then the SRH-6LoRH is removed.Else, if there is a next SRH-6LoRH of a Type with a larger or equal value,
meaning a same or lesser compression yielding same or larger compressed forms,
then the SRH-6LoRH is removed.Else, the first entry of the next SRH-6LoRH is popped from the next SRH-6LoRH
and coalesced with the first entry of this SRH-6LoRH.At the end of the process, if there is no more SRH-6LoRH in the packet, then
the processing node is the last router along the source route path.When receiving a packet with a SRH-6LoRH, a router determines the IPv6 address
of the current segment endpoint.If strict source routing is enforced and thus router is not the segment endpoint
for the packet then this router MUST drop the packet.If this router is the current segment endpoint, then the router pops its address
as described in and continues processing the packet.If there is still a SRH-6LoRH, then the router determines the new segment
endpoint and routes the packet towards that endpoint.Otherwise the router uses the destination in the inner IP header to forward or
accept the packet.The segment endpoint of a packet MUST be determined as follows:The router first determines the Compression Reference as discussed in
.The router then coalesces the Compression Reference with the first entry of the
first SRH-6LoRH header as discussed in . If the type of the
SRH-6LoRH header is type 4 then the coalescence is a full override.Since the Compression Reference is an uncompressed address, the coalesced IPv6
address is also expressed in the full 128bits.An example of this operation is provided in ., Section 11.2, specifies the RPL Packet Information (RPI) as
a set of fields that are placed by RPL routers in IP packets to identify the
RPL Instance, detect anomalies and trigger corrective actions.In particular, the SenderRank, which is the scalar
metric computed by a specialized Objective Function such as ,
indicates the Rank of the sender and is modified at each hop.
The SenderRank field is used to validate that the packet progresses
in the expected direction, either upwards or downwards, along the DODAG.RPL defines the RPL Option for Carrying RPL Information in Data-Plane Datagrams
to transport the RPI, which is carried in an
IPv6 Hop-by-Hop Options Header,
typically consuming eight bytes per packet.With , the RPL option is encoded as six octets, which must
be placed in a Hop-by-Hop header that consumes two additional octets
for a total of eight octets. To limit the header’s range to just the
RPL domain, the Hop-by-Hop header must be added to (or removed from)
packets that cross the border of the RPL domain.The 8-byte overhead is detrimental to LLN operation, in particular
with regards to bandwidth and battery constraints. These
bytes may cause a containing frame to grow above maximum frame size,
leading to Layer 2 or 6LoWPAN fragmentation, which in turn
leads to even more energy expenditure and issues discussed in
LLN Fragment Forwarding and Recovery.An additional overhead comes from the need, in certain cases,
to add an IP-in-IP encapsulation to carry the Hop-by-Hop header.
This is needed when the router that inserts the Hop-by-Hop header is not the
source of the packet, so that an error can be returned to the router. This
is also the case when a packet originated by a RPL node must be stripped from
the Hop-by-Hop header to be routed outside the RPL domain.For that reason, this specification defines an IP-in-IP-6LoRH header
in , but it must be noted that removal of a 6LoRH header
does not require manipulation of the packet in the LOWPAN_IPHC, and
thus, if the source address in the LOWPAN_IPHC is the node that
inserted the IP-in-IP-6LoRH header then this situation alone does not
mandate an IP-in-IP-6LoRH header.Note: A typical packet in RPL non-storing mode going down the RPL
graph requires an IP-in-IP encapsulation of the SRH, whereas the RPI
is usually (and quite illegally) omitted, unless
it is important to indicate the RPLInstanceID. To match this structure, an
optimized IP-in-IP 6LoRH header is defined in .As a result, a RPL packet may bear only an RPI-6LoRH header and no
IP-in-IP-6LoRH header. In that case, the source and destination of the
packet are specified by the LOWPAN_IPHC.As with , the fields in the RPI include an ‘O’, an ‘R’, and
an ‘F’ bit, an 8-bit RPLInstanceID (with some internal structure), and
a 16-bit SenderRank.The remainder of this section defines the RPI-6LoRH header, which is
a Critical 6LoWPAN Routing Header that is designed to transport the
RPI in 6LoWPAN LLNs.RPL Instances are discussed in , Section 5.
A number of simple use cases do not require more than one RPL Instance, and in
such cases, the RPL Instance is expected to be the Global Instance 0.
A global RPLInstanceID is encoded in a RPLInstanceID field as follows:For the particular case of the Global Instance 0, the
RPLInstanceID field is all zeros.
This specification allows to elide a RPLInstanceID field that is all
zeros, and defines a I flag that, when set, signals that the field is elided.The SenderRank is the result of the DAGRank operation on the rank of the
sender; here the DAGRank operation is defined in , Section 3.5.1, as:DAGRank(rank) = floor(rank/MinHopRankIncrease)If MinHopRankIncrease is set to a multiple of 256,
the least significant 8 bits of the SenderRank will be all zeroes; by
eliding those, the SenderRank can be compressed into a single byte.
This idea is used in by defining
DEFAULT_MIN_HOP_RANK_INCREASE as 256 and in that defaults
MinHopRankIncrease to DEFAULT_MIN_HOP_RANK_INCREASE.This specification allows to encode the SenderRank as either one or
two bytes, and defines a K flag that, when set, signals that a
single byte is used.The RPI-6LoRH header provides a compressed form for the RPL RPI.
Routers that need to forward a packet with a RPI-6LoRH header are
expected to be RPL routers that support this specification. If a
non-RPL router receives a packet with a RPI-6LoRH header, there was
a routing error and the packet should be dropped. Thus the Type field
MUST NOT be ignored.Since the I flag is not set, the TSE field does not need to be a
length expressed in bytes. In that case the field is fully reused
for control bits that encode the O, R and F flags from the RPI, as
well as the I and K flags that indicate the compression format.The Type for the RPI-6LoRH is 5.The RPI-6LoRH header is immediately followed by the RPLInstanceID field,
unless that field is fully elided, and then the SenderRank, which is
either compressed into one byte or fully in-lined as two
bytes. The I and K flags in the RPI-6LoRH header indicate whether the
RPLInstanceID is elided and/or the SenderRank is compressed.
Depending on these bits, the Length of the RPI-6LoRH may vary as
described hereafter.
The O, R, and F bits are defined in , section 11.2.
If it is set, the RPLInstanceID is elided and the
RPLInstanceID is the Global RPLInstanceID 0. If it is not set,
the octet immediately following the type field contains the
RPLInstanceID as specified in , section 5.1.
If it is set, the SenderRank is compressed into one octet,
with the least significant octet elided. If it is not set,
the SenderRank, is fully inlined as two octets.In , the RPLInstanceID is the Global RPLInstanceID 0,
and the MinHopRankIncrease is a multiple of 256 so the least significant
byte is all zeros and can be elided:In , the RPLInstanceID is the Global RPLInstanceID 0, but
both bytes of the SenderRank are significant so it can not be compressed:In , the RPLInstanceID is not the Global RPLInstanceID
0, and the MinHopRankIncrease is a multiple of 256:In , the RPLInstanceID is not the Global RPLInstanceID
0, and both bytes of the SenderRank are significant:The IP-in-IP 6LoRH (IP-in-IP-6LoRH) header is an Elective 6LoWPAN Routing Header
that provides a compressed form for the encapsulating
IPv6 Header in the case of an IP-in-IP encapsulation.An IP-in-IP encapsulation is used to insert a field such as a Routing Header or
an RPI at a router that is not the source of the packet. In order to send an
error back regarding the inserted field, the address of the router that performs
the insertion must be provided.The encapsulation can also enable the last router prior to Destination to
remove a field such as the RPI, but this can be done in the compressed form
by removing the RPI-6LoRH, so an IP-in-IP-6LoRH encapsulation is not required for
that sole purpose.This field is not critical for routing so the Type can be ignored, and the
TSE field contains the Length in bytes.The Length of an IP-in-IP-6LoRH header is expressed in bytes and MUST be at
least 1,
to indicate a Hop Limit (HL), that is decremented at each hop. When the HL
reaches 0, the packet is dropped per .If the Length of an IP-in-IP-6LoRH header is exactly 1, then the Encapsulator Address
is elided, which means that the Encapsulator is a well-known router, for
instance the root in a RPL graph.The most efficient compression of an IP-in-IP encapsulation that can be
achieved with this specification is obtained when an endpoint of the packet is
the root of the RPL DODAG associated to the RPL Instance that is used to
forward the packet, and the root address is known implicitly as opposed to
signaled explicitly in the data packets.If the Length of an IP-in-IP-6LoRH header is greater than 1, then an Encapsulator
Address is placed in a compressed form after the Hop Limit field.
The value of the Length indicates which compression is performed on the
Encapsulator Address. For instance, a Size of 3 indicates that the Encapsulator
Address is compressed to 2 bytes. The reference for the compression is the
address of the root of the DODAG. The way the address of the root is determined
is discussed in .With RPL, the destination address in the IP-in-IP header is implicitly the
root in the RPL graph for packets going upwards, and, in storing mode,
it is the destination address in the IPHC for packets going downwards.
In non-storing mode, there is no implicit value for packets going downwards.If the implicit value is correct, the destination IP address of the IP-in-IP
encapsulation can be elided. Else, the destination IP address of the IP-in-IP
header is transported in a SRH-6LoRH header as the first entry of the first of
these headers.If the final destination of the packet is a leaf that does not support
this specification, then the chain of 6LoRH headers must be stripped by the RPL/6LR router
to which the leaf is attached. In that example, the destination IP address of the
IP-in-IP header cannot be elided.In the special case where a 6LoRH header is used to route 6LoWPAN fragments,
the destination address is not accessible in the IPHC on all fragments and can be
elided only for the first fragment and for packets going upwards.The security considerations of , , and apply.Using a compressed format as opposed to the full in-line format is
logically equivalent and is believed to not create an opening for a new threat when
compared to , and .This specification reserves Dispatch Value Bit Patterns within
the 6LoWPAN Dispatch Page 1 as follows:101xxxxx: for Elective 6LoWPAN Routing Headers100xxxxx: for Critical 6LoWPAN Routing Headers.This document creates an IANA registry for the 6LoWPAN Routing Header Type,
and assigns the following values:0..4: SRH-6LoRH [RFCthis]5: RPI-6LoRH [RFCthis]6: IP-in-IP-6LoRH [RFCthis]The authors wish to thank Tom Phinney, Thomas Watteyne, Tengfei Chang, Martin Turon,
James Woodyatt, Samita Chakrabarti, Jonathan Hui, Gabriel Montenegro and Ralph Droms
for constructive reviews to the design in the 6lo Working Group.
The overall discussion involved participants to the 6MAN, 6TiSCH and ROLL
WGs, thank you all.
Special thanks to the chairs of the ROLL WG, Michael Richardson and Ines Robles,
and Brian Haberman, Internet Area A-D, and Adrian Farrel, Routing Area A-D,
for driving this complex effort across Working Groups and Areas.Key words for use in RFCs to Indicate Requirement LevelsIn many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements.Internet Protocol, Version 6 (IPv6) SpecificationThis document specifies version 6 of the Internet Protocol (IPv6), also sometimes referred to as IP Next Generation or IPng. [STANDARDS-TRACK]Transmission of IPv6 Packets over IEEE 802.15.4 NetworksThis document describes the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on IEEE 802.15.4 networks. Additional specifications include a simple header compression scheme using shared context and provisions for packet delivery in IEEE 802.15.4 meshes. [STANDARDS-TRACK]Compression Format for IPv6 Datagrams over IEEE 802.15.4-Based NetworksThis document updates RFC 4944, "Transmission of IPv6 Packets over IEEE 802.15.4 Networks". This document specifies an IPv6 header compression format for IPv6 packet delivery in Low Power Wireless Personal Area Networks (6LoWPANs). The compression format relies on shared context to allow compression of arbitrary prefixes. How the information is maintained in that shared context is out of scope. This document specifies compression of multicast addresses and a framework for compressing next headers. UDP header compression is specified within this framework. [STANDARDS-TRACK]RPL: IPv6 Routing Protocol for Low-Power and Lossy NetworksLow-Power and Lossy Networks (LLNs) are a class of network in which both the routers and their interconnect are constrained. LLN routers typically operate with constraints on processing power, memory, and energy (battery power). Their interconnects are characterized by high loss rates, low data rates, and instability. LLNs are comprised of anything from a few dozen to thousands of routers. Supported traffic flows include point-to-point (between devices inside the LLN), point-to-multipoint (from a central control point to a subset of devices inside the LLN), and multipoint-to-point (from devices inside the LLN towards a central control point). This document specifies the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL), which provides a mechanism whereby multipoint-to-point traffic from devices inside the LLN towards a central control point as well as point-to-multipoint traffic from the central control point to the devices inside the LLN are supported. Support for point-to-point traffic is also available. [STANDARDS-TRACK]Objective Function Zero for the Routing Protocol for Low-Power and Lossy Networks (RPL)The Routing Protocol for Low-Power and Lossy Networks (RPL) specification defines a generic Distance Vector protocol that is adapted to a variety of network types by the application of specific Objective Functions (OFs). An OF states the outcome of the process used by a RPL node to select and optimize routes within a RPL Instance based on the Information Objects available; an OF is not an algorithm.This document specifies a basic Objective Function that relies only on the objects that are defined in the RPL and does not use any protocol extensions. [STANDARDS-TRACK]The Routing Protocol for Low-Power and Lossy Networks (RPL) Option for Carrying RPL Information in Data-Plane DatagramsThe Routing Protocol for Low-Power and Lossy Networks (RPL) includes routing information in data-plane datagrams to quickly identify inconsistencies in the routing topology. This document describes the RPL Option for use among RPL routers to include such routing information. [STANDARDS-TRACK]An IPv6 Routing Header for Source Routes with the Routing Protocol for Low-Power and Lossy Networks (RPL)In Low-Power and Lossy Networks (LLNs), memory constraints on routers may limit them to maintaining, at most, a few routes. In some configurations, it is necessary to use these memory-constrained routers to deliver datagrams to nodes within the LLN. The Routing Protocol for Low-Power and Lossy Networks (RPL) can be used in some deployments to store most, if not all, routes on one (e.g., the Directed Acyclic Graph (DAG) root) or a few routers and forward the IPv6 datagram using a source routing technique to avoid large routing tables on memory-constrained routers. This document specifies a new IPv6 Routing header type for delivering datagrams within a RPL routing domain. [STANDARDS-TRACK]Terms Used in Routing for Low-Power and Lossy NetworksThis document provides a glossary of terminology used in routing requirements and solutions for networks referred to as Low-Power and Lossy Networks (LLNs). An LLN is typically composed of many embedded devices with limited power, memory, and processing resources interconnected by a variety of links. There is a wide scope of application areas for LLNs, including industrial monitoring, building automation (e.g., heating, ventilation, air conditioning, lighting, access control, fire), connected home, health care, environmental monitoring, urban sensor networks, energy management, assets tracking, and refrigeration.Terminology for Constrained-Node NetworksThe Internet Protocol Suite is increasingly used on small devices with severe constraints on power, memory, and processing resources, creating constrained-node networks. This document provides a number of basic terms that have been useful in the standardization work for constrained-node networks.6LoWPAN Paging DispatchThis specification introduces a new context switch mechanism for 6LoWPAN compression, expressed in terms of Pages and signaled by a new Paging Dispatch.IEEE std. 802.15.4, Part. 15.4: Wireless Medium Access Control (MAC) and Physical Layer (PHY) Specifications for Low-Rate Wireless Personal Area NetworksIEEE standard for Information TechnologyNeighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)The IETF work in IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) defines 6LoWPANs such as IEEE 802.15.4. This and other similar link technologies have limited or no usage of multicast signaling due to energy conservation. In addition, the wireless network may not strictly follow the traditional concept of IP subnets and IP links. IPv6 Neighbor Discovery was not designed for non- transitive wireless links, as its reliance on the traditional IPv6 link concept and its heavy use of multicast make it inefficient and sometimes impractical in a low-power and lossy network. This document describes simple optimizations to IPv6 Neighbor Discovery, its addressing mechanisms, and duplicate address detection for Low- power Wireless Personal Area Networks and similar networks. The document thus updates RFC 4944 to specify the use of the optimizations defined here. [STANDARDS-TRACK]Using IEEE 802.15.4e Time-Slotted Channel Hopping (TSCH) in the Internet of Things (IoT): Problem StatementThis document describes the environment, problem statement, and goals for using the Time-Slotted Channel Hopping (TSCH) Medium Access Control (MAC) protocol of IEEE 802.14.4e in the context of Low-Power and Lossy Networks (LLNs). The set of goals enumerated in this document form an initial set only.LLN Fragment Forwarding and RecoveryIn order to be routed, a fragmented packet must be reassembled at every hop of a multihop link where lower layer fragmentation occurs. Considering that the IPv6 minimum MTU is 1280 bytes and that an an 802.15.4 frame can have a payload limited to 74 bytes in the worst case, a packet might end up fragmented into as many as 18 fragments at the 6LoWPAN shim layer. If a single one of those fragments is lost in transmission, all fragments must be resent, further contributing to the congestion that might have caused the initial packet loss. This draft introduces a simple protocol to forward and recover individual fragments that might be lost over multiple hops between 6LoWPAN endpoints.An Architecture for IPv6 over the TSCH mode of IEEE 802.15.4This document describes a network architecture that provides low- latency, low-jitter and high-reliability packet delivery. It combines a high speed powered backbone and subnetworks using IEEE 802.15.4 time-slotted channel hopping (TSCH) to meet the requirements of LowPower wireless deterministic applications.When to use RFC 6553, 6554 and IPv6-in-IPv6This document states different cases where RFC 6553, RFC 6554 and IPv6-in-IPv6 encapsulation is required to set the bases to help defining the compression of RPL routing information in LLN environments.The example in illustrates the 6LoRH compression of
a classical packet in Storing Mode in all directions, as well
as in non-Storing mode for a packet going up the DODAG
following the default route to the root.
In this particular example, a fragmentation process takes place
per , and the fragment headers must be placed in
Page 0 before switching to Page 1:In Storing Mode, if the packet stays within the RPL domain, then it
is possible to save the IP-in-IP encapsulation, in which case only the
RPI is compressed with a 6LoRH, as illustrated in in the
case of a non-fragmented ICMP packet:The format in is logically equivalent to the
non-compressed format illustrated in :For a UDP packet, the transport header can be compressed with 6LoWPAN
HC as illustrated in :If the packet is received from the Internet in Storing Mode, then the root is
supposed to encapsulate the packet to insert the RPI. The resulting format
would be as represented in :The example illustrated in is a classical packet in non-Storing mode
for a packet going down the DODAG following a source routed path from the root.
Say that we have 4 forwarding hops to reach a destination. In the non-compressed
form, when the root generates the packet, the last 3 hops are encoded in a
Routing Header type 3 (SRH) and the first hop is the destination of the packet.
The intermediate hops perform a swap and the hop count indicates the current
active hop , .When compressed with this specification, the 4 hops are encoded in SRH-6LoRH
when the root generates the packet, and the final destination is left in the
LOWPAN-IPHC. There is no swap, and the forwarding node that corresponds to the
first entry effectively consumes it when forwarding, which means that the size
of the encoded packet decreases and that the hop information is lost.If the last hop in a SRH-6LoRH is not the final destination then it removes
the SRH-6LoRH before forwarding.In the particular example illustrated in , all addresses in the DODAG
are assigned from a same /112 prefix and the last 2 octets encoding an identifier
such as a IEEE 802.15.4 short address. In that case, all addresses can be
compressed to 2 octets, using the root address as reference. There will be
one SRH_6LoRH header, with, in this example, 3 compressed addresses:One may note that the RPI is provided. This is because the address of the root
that is the source of the IP-in-IP header is elided and inferred from the
RPLInstanceID in the RPI. Once found from a local context, that address is
used as Compression Reference to expand addresses in the SRH-6LoRH.With the RPL specifications available at the time of writing this draft, the root
is the only node that may incorporate a SRH in an IP packet. When the root forwards
a packet that it did not generate, it has to encapsulate the packet with IP-in-IP.But if the root generates the packet towards a node in its DODAG, then it should
avoid the extra IP-in-IP as illustrated in :Note: the RPI is not represented though RPL generally expects it.
In this particular case, since the Compression Reference for the SRH-6LoRH is the source
address in the LOWPAN-IPHC, and the routing is strict along the source route path,
the RPI does not appear to be absolutely necessary.In , all the nodes along the source route path share a same /112
prefix. This is typical of IPv6 addresses derived from an IEEE802.15.4 short
address, as long as all the nodes share a same PAN-ID. In that case, a type-1
SRH-6LoRH header can be used for encoding. The IPv6 address of the root is taken
as reference, and only the last 2 octets of the address of the intermediate hops
is encoded. The Size of 3 indicates 4 hops, resulting in a SRH-6LoRH of 10 bytes.This section illustrates the operation specified in
of forwarding a packet with a compressed SRH along an A->B->C->D source route
path. The operation of popping addresses is exemplified at each hop.