lpwan Working Group D. Barthel
Internet-Draft Orange SA
Intended status: Informational L. Toutain
Expires: May 1, 2018 Institut MINES TELECOM; IMT Atlantique
A. Kandasamy
Acklio
October 28, 2017
LPWAN Static Context Header Compression (SCHC) for ICMPv6
draft-barthel-icmpv6-schc-00
Abstract
ICMPv6 is a companion protocol to IPv6. It defines messages that
inform the source of IPv6 packets of errors during packet delivery.
It also defines the Echo Request/Reply messages that are used for
basic network troubleshooting (ping command). ICMPv6 messages are
transported on IPv6.
This document describes how to adapt ICMPv6 to Low Power Wide Area
Networks (LPWANs) by compressing ICMPv6/IPv6 headers and by
protecting the LPWAN network and the Device from undesirable ICMPv6
traffic.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 1, 2018.
Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
Barthel, et al. Expires May 1, 2018 [Page 1]
Internet-Draft LPWAN ICMPv6 compression October 2017
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Detailed behavior . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Device is the source of an ICMPv6 error message . . . . . 4
4.2. Device is the destination of an ICMPv6 error message . . 4
4.2.1. ICMPv6 error message compression. . . . . . . . . . . 5
4.3. Device does a ping . . . . . . . . . . . . . . . . . . . 6
4.4. Device is ping'ed . . . . . . . . . . . . . . . . . . . . 8
5. Traceroute . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
ICMPv6 [RFC4443] is a companion protocol to IPv6 [RFC8200].
[RFC4443] defines a generic message format. This format is used for
messages to be sent back to the source of an IPv6 packet to inform it
about errors during packet delivery.
More specifically, [RFC4443] defines 4 error messages: Destination
Unreachable, Packet Too Big, Time Exceeded and Parameter Problem.
[RFC4443] also defines the Echo Request and Echo Reply messages,
which provide support for the ping application.
Other ICMPv6 messages are defined in other RFCs, such as an extended
format of the same messages [RFC4884] and other messages used by the
Neighbor Discovery Protocol [RFC4861].
Barthel, et al. Expires May 1, 2018 [Page 2]
Internet-Draft LPWAN ICMPv6 compression October 2017
This document focuses on using Static Context Header Compression
(SCHC) to compress [RFC4443] messages that need to be transmitted
over the LPWAN network, and on having the LPWAN gateway proxying the
Device to save it the unwanted traffic.
LPWANs' salient characteristics are described in
[I-D.ietf-lpwan-overview]
2. Terminology
This draft re-uses the Terminology defined in
[I-D.ietf-lpwan-ipv6-static-context-hc].
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Use cases
In the LPWAN architecture, we can distinguish the following cases:
o the Device is the (purported) source of an ICMP error message,
mainly in response to an incorrect incoming IPv6 message, or in
response to a ping request. In this case, as much as possible,
the core SCHC C/D should act as a proxy and originate the ICMP
message, so that the Device and the LPWAN network are protected
from this unwanted traffic.
o the Device is the destination of the ICMP message, mainly in
response to a packet sent by the Device to the network that
generates an error. In this case, we want the ICMP message to
reach the Device, and this document describes in section
Section 4.2.1 what SCHC compression should be applied.
o the Device is the originator of an Echo Request message, and
therefore the destination of the Echo Reply message.
o the Device is the destination of an Echo Request message, and
therefore the purported source of an Echo Reply message.
These cases are further described in Section 4.
Barthel, et al. Expires May 1, 2018 [Page 3]
Internet-Draft LPWAN ICMPv6 compression October 2017
4. Detailed behavior
4.1. Device is the source of an ICMPv6 error message
As stated in [RFC4443], a node should generate an ICMPv6 message in
response to an IPv6 packet that is malformed or which cannot be
processed due to some incorrect field value.
The general intent of this document is to spare both the Device and
the LPWAN network this un-necessary traffic. The incorrect packets
should be caught at the core SCHC C/D and the ICMPv6 notification
should be sent back from there.
Device NGW core SCHC C/D Internet Host
| | | Destination Port=XXX |
| | |<---------------------------|
| | | |
| | |--------------------------->|
| | | ICMPv6 Port Unreachable |
| | | |
| | | |
Figure 1: Example of ICMPv6 error message sent back to the Internet
Figure 1 shows an example of an IPv6 packet trying to reach a Device.
Let's assume that the port number used as destination port is not
"known" (needs better definition) from the core SCHC C/D. Instead of
sending the packet over the LPWAN and having this packet rejected by
the Device, the core SCHC C/D issues an ICMPv6 error message
"Destination Unreachable" (Type 1) with Code 1 ("Port Unreachable")
on behalf of the Device.
TODO: This assumes that all ports that the Device listens to will be
matched by a SCHC rule. Is this the basic assumption of SCHC that
all packets that do not match a rule are rejected? If yes, why do
have fragmentation also for uncompressed packets?
TODO: discuss the various Type/Code that are expected to be generated
in response to various errors.
4.2. Device is the destination of an ICMPv6 error message
In this situation, we assume that a Device has been configured to
send information to a server on the Internet. If this server becomes
no longer accessible, an ICMPv6 message will be generated back
Barthel, et al. Expires May 1, 2018 [Page 4]
Internet-Draft LPWAN ICMPv6 compression October 2017
towards the Device by an intermediate router. This information can
be useful to the Device, for example for reducing the reporting rate
in case of periodic reporting of data. Therefore, we compress the
ICMPv6 message using SCHC and forward it to the Device over the
LPWAN.
Device NGW core SCHC C/D Internet Server
| | | |
| SCHC compressed IPv6 | |
|~~~~~~~~~~~|----------->|----------------------X |
| | | <--------------------- |
|<~~~~~~~~~~|------------| ICMPv6 Host unreachable |
|SCHC compressed ICMPv6 | |
| | | |
| | | |
Figure 2: Example of ICMPv6 error message sent back to the Device
Figure 2 illustrates this behavior. The ICMPv6 error message is
compressed as described in Section 4.2.1 and forwarded over the LPWAN
to the Device.
4.2.1. ICMPv6 error message compression.
The ICMPv6 error messages defined in [RFC4443] contain the fields
shown in Figure 3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| As much of invoking packet |
+ as possible without the ICMPv6 packet +
| exceeding the minimum IPv6 MTU |
Figure 3: ICMPv6 Error Message format
[RFC4443] states that Type can take the values 1 to 4, and Code can
be set to values between 0 and 6. Value is unused for the
Destination Unreachable and Time Exceeded messages. It contains the
MTU for the Packet Too Big message and a pointer to the byte causing
Barthel, et al. Expires May 1, 2018 [Page 5]
Internet-Draft LPWAN ICMPv6 compression October 2017
the error for the Parameter Error message. Therefore, Value is never
expected to be greater than 1280 in LPWAN networks.
The following generic rule can therefore be used to compress all
ICMPv6 error messages as defined today. More specific rules can also
be defined to achieve better compression of some error messages.
The Type field can be associated to a matching list [1, 2, 3, 4] and
is therefore compressed down to 2 bits. Code can be reduced to 3
bits using the LSB CDA. Value can be sent on 11 bits using the LSB
CDA, but if the Device is known to send smaller packets, then the
size of this field can be further reduced.
By [RFC4443], the rest of the ICMPv6 message must contain as much as
possible of the IPv6 offending (invoking) packet that triggered this
ICMPv6 error message. This information is used to try and identify
the SCHC rule that was used to decompress the offending IPv6 packet.
If the rule can be found then the Rule Id is added at the end of the
compressed ICMPv6 message. Otherwise the compressed packet ends with
the compressed Value field.
[RFC4443] states that the "ICMPv6 error message MUST include as much
of the IPv6 offending (invoking) packet ... as possible". In order
to comply with this requirement, if there is enough information in
the incoming ICMPv6 message for the core SCHC C/D to identify the
rule that has been used to decompress the erroneous IPv6 packet, this
Rule Id must be sent in the compressed ICMPv6 message to the Device.
TODO: the erroneous IPv6 packet header (not just the Rule Id) should
be sent back. This includes the Rule Id and the compression residue.
This means the SCHC C/D uses the context backwards (in the reverse
direction). How does the Device know it must also use the context
backwards?
TODO: how does one know that the "payload" of a compressed-header
packet is in fact another compressed header?
4.3. Device does a ping
If a ping request is generated by a Device, then SCHC compression
applies.
The format of an ICMPv6 Echo Request message is described in
Figure 4, with Type=128 and Code=0.
Barthel, et al. Expires May 1, 2018 [Page 6]
Internet-Draft LPWAN ICMPv6 compression October 2017
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Code | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data ...
+-+-+-+-+-
Figure 4: ICMPv6 Echo Request message format
If we assume that one rule will be devoted to compressing Echo
Request messages, then Type and Code are known in the rule to be 128
and 0 and can therefore be elided with the not-sent CDA.
Checksum can be reconstructed with the compute-checksum CDA and
therefore is not transmitted.
[RFC4443] states that Identifier and Sequence Number are meant to
"aid in matching Echo Replies to this Echo Request" and that they
"may be zero". Data is "zero or more bytes of arbitrary data".
We recommend that Identifier be zero, Sequence Number be a counter on
3 bits, and Data be zero bytes (absent). Therefore, Identifier is
elided with the not-sent CDA, Sequence Number is transmitted on 3
bits with the LSB CDA and no Data is transmitted.
The transmission cost of the Echo Request message is therefore the
size of the Rule Id + 3 bits.
When the destination receives the Echo Request message, it will
respond back with a Echo Reply message. This message bears the same
format as the Echo Request message but with Type = 129 (see
Figure 4).
[RFC4443] states that the Identifier, Sequence Number and Data fields
of the Echo Reply message shall contain the same values as the
invoking Echo Request message. Therefore, a rule shall be used
similar to that used for compressing the Echo Request message.
TODO: how about a shared rule for Echo Request and Echo Reply with an
LSB(1) CDA on the Type field? Or exploiting the Up/Down direction
field in the rule?
Barthel, et al. Expires May 1, 2018 [Page 7]
Internet-Draft LPWAN ICMPv6 compression October 2017
4.4. Device is ping'ed
If the Device is ping'ed (i.e., is the destination of an Echo Request
message), the default behavior is to avoid propagating the Echo
Request message over the LPWAN.
This is the recommended behavior with the Code 0 (default value) of
the Echo Request message. In addition, this document defines two
other Code values to achieve two other behaviors.
The resulting three behaviors are shown on Figure 5 and described
below:
Device NGW core SCHC C/D Internet Host
| | | Echo Request, Code=0 |
| | |<---------------------------|
| | | |
| | |--------------------------->|
| | | Echo Reply, Code=0 |
| | | |
| | | Echo Request, Code=1 |
| |<==========>|<---------------------------|
| | | |
| | |--------------------------->|
| | | Echo Reply, Code=1 |
| | | last seen |
| | | |
| | | Echo Request, Code=2 |
|<~~~~~~~~~~|------------|<---------------------------|
| | | |
|~~~~~~~~~~~|----------->|--------------------------->|
| | | Echo Reply, Code=2 |
| | | last seen |
| | | |
Figure 5: Examples of ICMPv6 Echo Request/Reply
o Code = 0: The Echo Request message is not propagated on the LPWAN
to the Device. If the SCHC C/D finds a rule in the context with
the IPv6 address of the Device, it responds with an Echo Reply on
behalf of the Device. If no rule is found with that IPv6 address,
the SCHC C/D does not respond.
TODO: again, we are assuming that no compression rule is equivalent
to the device not providing the service.
Barthel, et al. Expires May 1, 2018 [Page 8]
Internet-Draft LPWAN ICMPv6 compression October 2017
o Code = 1: the SCHC C/D queries the NGW (or maintains a local
database) and answers with the number of seconds since the Device
last transmission.
TODO: what does it mean to answer "with the number of seconds ..."?
There is no such field in an Echo Reply message. Do we overwrite one
of the fields (Identifier, Sequencer Number, Data)? They are all
supposed to be copied from the Echo Request. Do we change their
definition with Code==1 or Code==2?
o Code = 2: the SCHC C/D compresses the ICMPv6 message and forwards
it to the Device. The Echo Reply message sent by the Device is
also compressed. Since the Echo Request message comes from the
Internet, the values of the Identifier, Sequence Number and Data
fields cannot be known in advance, and therefore must be
transmitted. However, it is likely that the Echo Request with
Code 2 will be firewalled from the Internet and restricted to
authorized users. Therefore, the Echo Request message can be
assumed to have the same content as recommended in Section 4.3,
and the same compression rules apply.
5. Traceroute
The traceroute6 program sends successive probe packets destined to a
chosen target but with the Hop Limit value successively incremented
from the initial value 1.
It expects to receive a "Time Exceeded" (Type = 3) "Hop Limit" (Code
= 0) ICMPv6 error message back from the successive routers along the
path to the destination.
The probe packet is usually a UDP datagram, but can also be a TCP
datagram or even an ICMPv6 message. The destination port is chosen
in the unassigned range in hope that the destination, when eventually
reached, will respond with a "Destination Unreachable" (Type = 1)
"Port Unreachable" (Code = 4) ICMPv6 error message.
It is not anticipated that a Device will want to traceroute a
destination on the Internet.
By contrast, a host on the Internet may attempt to traceroute an IPv6
address that is assigned to an LPWAN device. This is described in
Figure 6.
Barthel, et al. Expires May 1, 2018 [Page 9]
Internet-Draft LPWAN ICMPv6 compression October 2017
Device NGW core SCHC C/D Internet
| | | Hop Limit=1, Dest Port=XXX |
| | |<---------------------------|
| | | |
| | |--------------------------->|
| | | ICMPv6 Hop Limit error |
| | | |
| | | |
| | | Hop Limit=2, Dest Port=XXX |
| | |<---------------------------|
| | | |
| | |--------------------------->|
| | | ICMPv6 Port Unreachable |
Figure 6: Example of traceroute to the LPWAN Device
When the probe packet first reaches the core SCHC C/D, its remaining
Hop Limit is 1. The core SCHC C/D will respond back with a "Time
Exceeded" (Type = 3) "Hop Limit" (Code = 0) ICMPv6 error message.
Later on, when the probe packet reaches the code SCHC C/D with a Hop
Limit value of 2, the core SCHC C/D will, as explained in
Section 4.1, answer back with a "Destination Unreachable" (Type = 1)
"Port Unreachable" (Code = 4) ICMPv6 error message. This is what the
traceroute6 command expects. Therefore, the traceroute6 command will
work with LPWAN IPv6 destinations, except for the time displayed for
the destination, which is actually the time to its proxy.
However, if the probe packet happens to hit a port that matches a
SCHC rule for that Device, the packet will be compressed with this
rule and sent over the LPWAN, which is unfortunate. Forwarding of
packets to the Device over the LPWAN should only be done from
authenticated/trusted sources anyway. Rate-limitation on top of
authentication will mitigate this nuisance.
6. Security considerations
TODO
7. IANA Considerations
TODO
Barthel, et al. Expires May 1, 2018 [Page 10]
Internet-Draft LPWAN ICMPv6 compression October 2017
8. References
8.1. Normative References
[I-D.ietf-lpwan-ipv6-static-context-hc]
Minaburo, A., Toutain, L., and C. Gomez, "LPWAN Static
Context Header Compression (SCHC) and fragmentation for
IPv6 and UDP", draft-ietf-lpwan-ipv6-static-context-hc-07
(work in progress), October 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, <https://www.rfc-
editor.org/info/rfc2119>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", STD 89,
RFC 4443, DOI 10.17487/RFC4443, March 2006,
<https://www.rfc-editor.org/info/rfc4443>.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
DOI 10.17487/RFC4861, September 2007, <https://www.rfc-
editor.org/info/rfc4861>.
[RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
"Extended ICMP to Support Multi-Part Messages", RFC 4884,
DOI 10.17487/RFC4884, April 2007, <https://www.rfc-
editor.org/info/rfc4884>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017, <https://www.rfc-
editor.org/info/rfc8200>.
8.2. Informative References
[I-D.ietf-lpwan-overview]
Farrell, S., "LPWAN Overview", draft-ietf-lpwan-
overview-07 (work in progress), October 2017.
Barthel, et al. Expires May 1, 2018 [Page 11]
Internet-Draft LPWAN ICMPv6 compression October 2017
Authors' Addresses
Dominique Barthel
Orange SA
28 chemin du Vieux Chene
BP 98
38243 Meylan Cedex
France
Email: dominique.barthel@orange.com
Laurent Toutain
Institut MINES TELECOM; IMT Atlantique
2 rue de la Chataigneraie
CS 17607
35576 Cesson-Sevigne Cedex
France
Email: laurent.toutain@imt-atlantique.fr
Arunprabhu Kandasamy
Acklio
2bis rue de la Chataigneraie
35510 Cesson-Sevigne Cedex
France
Email: arun@ackl.io
Barthel, et al. Expires May 1, 2018 [Page 12]