ESP Header Compression Profile
draft-ietf-ipsecme-diet-esp-03
| Document | Type | Active Internet-Draft (ipsecme WG) | |
|---|---|---|---|
| Authors | Daniel Migault , Maryam Hatami , Sandra Cespedes , J. William Atwood , Tobias Guggemos , Carsten Bormann , David Schinazi | ||
| Last updated | 2025-01-08 (Latest revision 2024-11-24) | ||
| Replaces | draft-mglt-ipsecme-diet-esp | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | In WG Last Call | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-ipsecme-diet-esp-03
IPsecme D. Migault
Internet-Draft Ericsson
Intended status: Standards Track M. Hatami
Expires: 29 May 2025 S. Céspedes
W. Atwood
Concordia University
T. Guggemos
LMU
C. Bormann
Universitaet Bremen TZI
D. Schinazi
Google LLC
25 November 2024
ESP Header Compression Profile
draft-ietf-ipsecme-diet-esp-03
Abstract
The document specifies Diet-ESP, an ESP Header Compression Profile
(EHCP) that compresses IPsec/ESP communications using Static Context
Header Compression (SCHC).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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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 29 May 2025.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. SCHC Integration into the IPsec Stack . . . . . . . . . . . . 6
4.1. SCHC Parameters for Diet-ESP . . . . . . . . . . . . . . 8
4.2. Set of Rules (SoR) for Diet-ESP . . . . . . . . . . . . . 10
4.3. Attributes for Rules Generation . . . . . . . . . . . . . 10
4.3.1. Compression/Decompression Actions in Diet-ESP . . . . 15
5. SCHC Compression for IPsec in Tunnel mode . . . . . . . . . . 16
5.1. Inner IP Compression (IIPC) . . . . . . . . . . . . . . . 16
5.1.1. Inner IP Payload Compression . . . . . . . . . . . . 16
5.1.2. Inner IPv6 Header Compression . . . . . . . . . . . . 16
5.1.3. Inner IPv4 Header Compression . . . . . . . . . . . . 18
5.2. ESP Data Byte alignment . . . . . . . . . . . . . . . . . 19
5.3. Clear Text ESP Compression (CTEC) . . . . . . . . . . . . 19
5.4. Encrypted ESP Compression (EEC) . . . . . . . . . . . . . 19
6. SCHC Compression for IPsec in Transport mode . . . . . . . . 20
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
8. Security Considerations . . . . . . . . . . . . . . . . . . . 21
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1. Normative References . . . . . . . . . . . . . . . . . . 21
10.2. Informative References . . . . . . . . . . . . . . . . . 23
Appendix A. Appendix . . . . . . . . . . . . . . . . . . . . . . 23
A.1. JSON Representation of SCHC Rules for Diet-ESP Header
Compression . . . . . . . . . . . . . . . . . . . . . . . 23
A.2. Example Outcome . . . . . . . . . . . . . . . . . . . . . 26
A.2.1. Input Packet . . . . . . . . . . . . . . . . . . . . 26
A.2.2. Compression Process . . . . . . . . . . . . . . . . . 26
A.2.3. Decompression Process . . . . . . . . . . . . . . . . 27
A.2.4. Final Output Packet . . . . . . . . . . . . . . . . . 28
A.2.5. GitHub Repository: Diet-ESP SCHC Implementation . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
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1. Requirements notation
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.
2. Introduction
The Encapsulating Security Payload (ESP) [RFC4303] protocol is part
of the IPsec [RFC4301] suite of protocols and can provide
confidentiality, data origin authentication, integrity, anti-replay,
and traffic flow confidentiality. The set of services ESP provides
depends on the Security Association (SA) parameters negotiated
between devices.
An ESP packet is composed of the ESP Header, the ESP Payload, the ESP
Trailer, and the Integrity Check Value (ICV). ESP has two modes of
operation: Transport and Tunnel. In Transport mode, the ESP Payload
consists of the payload of the original IP packet; the ESP Header is
inserted after the original IP packet header. In Tunnel mode,
commonly used for VPNs, the ESP Header is placed after an outer IP
header and before the inner IP packet headers of the original
datagram. This ensures both the original IP headers and payload are
protected. Consequently, the ESP Payload field contains either the
payload from the original IP packet or the fully-encapsulated IP
packet, in transport mode or tunnel mode, respectively.
The ESP Trailer, placed at the end of the encrypted payload, includes
fields such as Padding and Pad Length to ensure proper alignment, and
Next Header to indicate the protocol following the ESP header. The
ICV, calculated over the ESP Header, ESP Payload, and ESP Trailer, is
appended after the ESP Trailer to ensure packet integrity. For a
simplified overview of ESP, readers are referred to Minimal ESP
[RFC9333].
While ESP is effective in securing traffic, further optimization can
reduce packet sizes, enhancing performance in networks with limited
bandwidth. In such environments, reducing the size of transmitted
packets is essential to improve efficiency. This document defines
the ESP Header Compression Profile (EHCP), namely Diet-ESP, for
compression/decompression (C/D) of IPsec/ESP [RFC4301] / [RFC4303]
packets using the Static Context Header Compression and Fragmentation
(SCHC) framework [RFC8724]. The structure of Diet-ESP is shown in
Figure 1. Compression with SCHC is based on the use of a Set of
Rules (SoR) used in a SCHC instance for C/D operations
[I-D.ietf-schc-architecture]. One or more SoR constitute the SCHC
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Context. In the case of IPsec, the Context can be agreed via IKEv2
[RFC7296] and its specific extension
[I-D.ietf-ipsecme-ikev2-diet-esp-extension].
As a result of the application of the same SoR, header values shared
by the end-points do not need to be sent on the wire. At the
receiver, header information is re-generated from the received
compressed packet and the application of the proper SoR retrieved
from the Context.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| Security Parameters Index (SPI) | ^Int.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Cov-
| Sequence Number | |ered
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ----
| Payload Data* (variable) | | ^
~ ~ | |
| | |Conf.
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |Cov-
| | Padding (0-255 bytes) | |ered*
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | |
| | Pad Length | Next Header | v v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ------
| Integrity Check Value-ICV (variable) |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Top-Level Format of an ESP Packet
This document defines the ESP Header Compression profile (EHCP)
Architecture with the application of SCHC at various layers of the
IPsec stack---also called SCHC strata---as defined below:
1. Inner IP Compression (IIPC): The SoR used in this SCHC stratum
apply directly to the headers of the inner IP packet. For
example, in the case of a UDP packet with ports determined by the
SA, fields such as UDP ports and checksums are typically
compressed. If no compression of the inner packet is possible,
the resulting SCHC packet contains the uncompressed IP packet, as
per [RFC8724], Section 7.2.
2. Clear Text ESP Compression (CTEC): This SCHC stratum contains SoR
that compress the fields of the ESP Payload, right before being
encrypted, as the encapsulated traffic in tunnel mode.
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3. Encrypted ESP Compression (EEC): This SCHC stratum contains SoR
that compress the ESP fields that remain visible after
encryption, that is, the ESP Header.
Note that the descriptions of the three SCHC strata provided in this
document meet the general purpose of ESP. It is possible that in
some deployments, the SCHC instances from different SCHC layers can
be merged. Typically, a specific implementation may merge the
compression of IIPC and CTEC layers.
Each SoR indicates the ESP header fields to be matched by the rules.
The SCHC instances define how the SCHC Context is initialized from
the SA and generate the corresponding SCHC rules (i.e., RuleID, SCHC
MAX_PACKET_SIZE, new SCHC Compression/Decompression Actions (CDA),
and fragmentation). The appendix provides illustrative examples of
applications of EHCP implemented with the OpenSCHC [OpenSCHC].
3. Terminology
ESP Header Compression Profile (EHCP): A method to reduce the size
of ESP headers using predefined compression rules and contexts to
improve efficiency.
ESP Trailer: A set of fields added at the end of the ESP payload,
including Padding, Pad Length, and Next Header, used to ensure
alignment and indicate the next protocol.
SCHC Stratum: Refers to the specific layer in the ESP packet
structure where the Set of Rules of a SCHC instance are applied
for compression and decompression.
Inner IP C/D (IIPC): Expressed via the SCHC framework, IIPC
compresses/decompresses the inner IP packet headers.
Clear Text ESP C/D (CTEC): Expressed via the SCHC framework, CTEC
compresses/decompresses all fields that will later be encrypted by
ESP, which include the ESP Data and ESP Trailer.
Encrypted ESP C/D (EEC): Expressed via the SCHC framework, EEC
compresses/decompresses ESP fields that will not be encrypted by
ESP.
Security Parameters Index (SPI): As defined in [RFC4301],
Section 4.1.
Sequence Number (SN): As defined in [RFC4303], Section 2.2.
Static Context Header Compression (SCHC): A framework for header
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compression designed for LPWANs, as defined in [RFC8724].
Static Context Header Compression Rules (SCHC Rules): As defined in
[RFC8724], Section 5.
RuleID: A unique identifier for each SCHC rule, as defined in
[RFC8724], Section 5.1.
SCHC Context: The set of rules shared between communicating
entities, as defined in [RFC8724], Section 5.3.
SCHC Parameters: A set of predefined values used for SCHC
compression and decompression, ensuring byte alignment and proper
packet formatting based on the SCHC profile.
SCHC MAX_PACKET_SIZE: The maximum size of a SCHC-compressed packet
that can be transmitted without fragmentation.
Traffic Selector (TS): A set of parameters (e.g., IP address range,
port range, and protocol) used to define which traffic should be
protected by a specific Security Association (SA).
It is assumed that the reader is familiar with other SCHC terminology
defined in [RFC8376], [RFC8724], and [I-D.ietf-schc-architecture].
4. SCHC Integration into the IPsec Stack
The main principle of the ESP Header Compression Profile (EHCP) is to
avoid sending information that has already been shared by the peers.
Different profiles and technologies, such as those defined by
[RFC4301] and [RFC4303], ensure that ESP can be tailored to various
network requirements and security policies. However, ESP is not
optimized for bandwidth efficiency because it has been designed as a
general-purpose protocol. EHCP aims to address this by leveraging a
profile, expressed via the SCHC architecture, to optimize the ESP
header sizes for better efficiency in constrained environments.
Figure 2 illustrates the integration of SCHC into the IPsec stack,
detailing the different layers and components involved in the
compression and decompression processes. The diagram is divided into
two entities, each representing an endpoint of a communication link.
Rules for compression are derived from parameters associated with the
Security Association (SA) and agreed upon via IKEv2 [RFC7296], as
well as specific compression parameters designated as Attributes for
Rules Generation (AfRG) (see Section 4.3). These AfRGs are also
agreed upon via IKEv2 in [I-D.ietf-ipsecme-ikev2-diet-esp-extension].
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Upon establishing the SA, Diet-ESP uses the AfRGs listed in Table 1
for derivation of the SoR applicable to each SCHC stratum. The
collection of rules are then used for the SCHC Context
initialization. The reference column in Table 1 indicates the source
where the parameter value is defined. The C/D column specifies in
which of the SCHC strata the parameter is being used.
EHCP defines three SCHC strata for compression: Inner IP Compression
(IIPC), Clear Text ESP Compression (CTEC), and Encrypted ESP
Compression (EEC). The compression operations for each stratum are
described in Section 5.1, Section 5.3, and Section 5.4.
EHCP essentially limits the scope of the compression to the inner IP
headers and specific fields such as ports and checksums of transports
like UDP, UDP-Lite, TCP, SCTP. Further and more specific compression
profiles may be defined in the future to cover compression of headers
of different upper layer protocols.
At the receiver endpoint, the decompression of the inbound packet
follows a reverse process. First, the Encrypted ESP C/D (EEC)
decompresses the encrypted ESP header fields. After the ESP packet
is decrypted, the Clear Text ESP C/D (CTEC) decompresses the Clear
Text fields of the ESP packet.
Note that implementations MAY differ from the architectural
description but it is assumed that the outputs will be the same.
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+--------------------------------+
| ESP Header Compression Context |
| - Security Association |
| - Additional Parameters |
+--------------------------------+
|
Endpoint | Endpoint
|
+-----------------+ | +-----------------+
| Inner IP packet | | | Inner IP packet |
+-----------------+ | +-----------------+
| SCHC(IIP + UDP | | | SCHC(IIP + UDP |
| or ...) |+--------IIPC layer-----------+| or ...) |
+-----------------+ C {IIP} +-----------------+
| ESP | | | ESP |
| (Encapsulation) | | | (unwrapping) |
+-----------------+ | +-----------------+
| SCHC | v | SCHC |
| (ESP Payload) |+--------- CTEC layer --------+| (ESP Payload) |
+-----------------+ EH, C {C {IIP}, ET} +-----------------+
| ESP | | | ESP |
| (Encryption) | | | (decryption) |
+-----------------+ v +-----------------+
| SCHC(ESP Header)|+--------- EEC layer ---------+| SCHC(ESP Header)|
+-----------------+ IP, C {EH, C {C {IIP}, ET}} +-----------------+
| IPv6 + ESP | | IPv6 + ESP |
+-----------------+ +-----------------+
| L2 | | L2 |
+-----------------+ +-----------------+
Figure 2: SCHC Integration into the IPsec Stack. Packets are
described for IPsec in tunnel mode. C designates the Compressed
header for the fields inside. IIP refers to the Inner IP packet,
EH refers to the ESP Header, and ET refers to the ESP Trailer.
The labels “SCHC (IIPC: Compress Inner IP),” “SCHC (CTEC:
Compress Trailer),” and “SCHC (EEC: Compress ESP Header)” are
added to indicate that different SCHC instances are applied at
the IIPC, CTEC, and EEC layers, respectively.
4.1. SCHC Parameters for Diet-ESP
A SCHC compressed packet is always in the form:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+---------...----------+~~~~~~~~~+---------------+
| RuleID | Compression Residue | Payload | SCHC padding |
+-+-+-+-+-+-+-+---------...----------+~~~~~~~~~+---------------+
|-------- Compressed Header ---------| |-- as needed --|
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Figure 3: Diet-ESP Compressed Header Format
The SCHC Profile for Diet-ESP is defined as follows:
RuleID: The RuleID is a unique identifier for each SCHC rule. It is
included in packets to ensure the receiver applies the correct
decompression rule, maintaining consistency in packet processing.
Note that the Rule ID does not need to be explicitly agreed upon
and can be defined independently by each party. The RuleID in
Diet-ESP is expressed as 1 byte.
Maximum Packet Size: MAX_PACKET_SIZE is determined by the specific
IPsec ESP configuration and the underlying transport, but it is
typically aligned with the network’s MTU. The size constraints
are optimized based on the available link capacity and negotiated
parameters between endpoints.
SCHC Padding: Padding in SCHC is used to align data to a specific
boundary (typically byte-aligned or 8-bit aligned) to meet the
requirements of the underlying link layer protocol or encryption
algorithm. Padding bits are often zero or follow a pattern but do
not contain significant data. In Diet-ESP, the SCHC padding is
added in the CTEC strata to align the packet for encryption.
The resulting IP/ESP packet size is variable. In some networks, the
packet will require fragmentation before transmission over the wire.
Fragmentation is out of the scope of this document since it is
dependent on the layer 2 technology.
Figure 4 illustrates how the final compressed packet looks when using
SCHC compression for ESP headers in the Diet-ESP profile.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SCHC EEC Header (EEC stratum) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| SCHC CTEC Header (CTEC stratum) | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| SCHC IIP Header (IIPC stratum) | |
+---------------------------------------------------------------+ En-
| Inner IP Payload Data* (variable) | cry-
~ ~ pted
| | |
+---------------------------------------------------------------+ |
| SCHC CTEC Padding | v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ----
| |
| ICV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Diet-ESP Compressed Packet Format with SCHC
4.2. Set of Rules (SoR) for Diet-ESP
SCHC SoR are predefined sets of instructions that specify how to
compress and decompress the header fields of an ESP packet. The
identification of a particular SoR will follow the specification in
[I-D.ietf-schc-architecture].
Similarly to the SA, Rules are directional and the Direction
Indicator (DI) is set to Up for outbound SA and Down for inbound SA.
Each Rule also contains a Field Position parameter that is set to 1,
unless specified otherwise.
4.3. Attributes for Rules Generation
The list of attributes for the Rules Generation (AfRG) is shown in
Table 1. These attributes are used to express the various
compressions that operate at the IIPC, CTEC, and EEC layers.
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The compression of the Inner IP Packet is based on the attributes
that are derived from the negotiated Traffic Selectors TSi/TSr, as
described in [RFC7296], Section 3.13. The Traffic Selectors may
result in a quite complex expression, and this specification
restricts that complexity. In particular, Diet-ESP restricts the
Traffic Selector to a single type of IP address (i.e., IPv4 or IPv6),
a single protocol (such as UDP, TCP, or not relevant), a single port
range, and multiple DSCP numbers. Such simplification corresponds to
the expression of an individual Traffic Selector Payload [RFC7296],
Section 3.13.1.
The ability to derive the EHCP Context for the IIPC from the agreed
Traffic Selectors is indicated by the variable iipc_profile.
+===================+==========================+===========+=======+
| EHC Context | Possible Values | Reference | C / D |
+===================+==========================+===========+=======+
| iipc_profile | "diet-esp", "uncompress" | ThisRFC | N/A |
+-------------------+--------------------------+-----------+-------+
| dscp_cda | "uncompress", "lower", | ThisRFC | IIPC |
| | "sa" | | |
+-------------------+--------------------------+-----------+-------+
| ecn_cda | "uncompress", "lower" | ThisRFC | IIPC |
+-------------------+--------------------------+-----------+-------+
| flow_label_cda | "uncompress", "lower", | ThisRFC | IIPC |
+-------------------+--------------------------+-----------+-------+
| | "generated", "zero" | | |
+-------------------+--------------------------+-----------+-------+
| ts_ip_version | "IPv4-only IPv6-only" | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_ip_src_start | IP4 or IPv6 address | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_ip_src_end | IP4 or IPv6 address | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_ip_dst_start | IPv4 or IPv6 address | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_ip_dst_end | IPv4 or IPv6 address | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_proto | TCP, UDP, UDP-Lite, | RFC7296 | IIPC |
| | SCTP, | | |
+-------------------+--------------------------+-----------+-------+
| | ANY, ... | | |
+-------------------+--------------------------+-----------+-------+
| ts_port_src_start | Port number | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_port_src_end | Port number | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| ts_port_dst_start | Port number | RFC7296 | IIPC |
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+-------------------+--------------------------+-----------+-------+
| ts_port_dst_end | Port number | RFC7296 | IIPC |
+-------------------+--------------------------+-----------+-------+
| dscp_list | list of DSCP numbers | RFCYYYY | IIPC |
+-------------------+--------------------------+-----------+-------+
| alignment | "8 bit", "16 bit", "32 | ThisRFC | CTEC |
| | bit" | | |
+-------------------+--------------------------+-----------+-------+
| | "64 bit" | | |
+-------------------+--------------------------+-----------+-------+
| ipsec_mode | "Tunnel", "Transport" | RFC4301 | CTEC |
+-------------------+--------------------------+-----------+-------+
| tunnel_ip | IPv6 address | RFC4301 | CTEC |
+-------------------+--------------------------+-----------+-------+
| esp_encr | ESP Encryption Algorithm | RFC4301 | CTEC |
+-------------------+--------------------------+-----------+-------+
| esp_spi | ESP SPI | RFC4301 | EEC |
+-------------------+--------------------------+-----------+-------+
| esp_spi_lsb | 0-32 | ThisRFC | EEC |
+-------------------+--------------------------+-----------+-------+
| esp_sn | ESP Sequence Number | RFC4301 | EEC |
+-------------------+--------------------------+-----------+-------+
| esp_sn_lsb | 0-64 | ThisRFC | EEC |
+-------------------+--------------------------+-----------+-------+
Table 1: EHCP related parameters
Any parameter starting with "ts_" is associated with the Traffic
Selectors of the SA. The notation is introduced by this
specification but the definition of the parameters is in [RFC4301]
and [RFC7296].
This specification limits the expression of the Traffic Selector to
be of the form (IP source range, IP destination range, Port source
range, Port destination range, Protocol ID list, DSCP list). This
limits the original flexibility of the expression of TS, but provides
sufficient flexibility.
The details of each parameter are the following:
iipc_profile: designates the profile used by IIPC. When set to
"uncompress" IIPC is not performed. This specification describes
IIPC that corresponds to the "diet-esp" profile.
flow_label_cda: indicates how the Flow Label field of the inner IPv6
packet or the Identification field of the inner IPv4 packet is
compressed / decompressed - See Section 4.3.1 for more
information. In a nutshell, "uncompress" indicates that Flow
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Label (resp. Identification) are not compressed. "lower"
indicates the value is read from the outer IP header - eventually
with some adaptations when inner IP packet and outer IP packets
have different versions. "generated" indicates that the field is
generated by the receiving party. In that case, the decompressed
value may take a different value compared to its original value.
"zero" indicates the field is set to zero.
dscp_cda: indicates how the DSCP values of the inner IP packet are
generated. (See flow_label_cda). "sa" indicates, compression is
performed according to the DSCP values agreed by the SA
(dscp_list).
ecn_cda: indicates how the ECN values of the inner IP packet are
generated. (See flow_label_cda).
ts_ip_version: designates the IP version of the Traffic Selectors
and its value is set to "IPv4-only" when only IPv4 IP addresses
are considered and to "IPv6-only" when only IPv6 addresses are
considered. Practically, when IKEv2 is used, it means that the
agreed TSi or TSr results only in a mutually exclusive combination
of TS_IPV4_ADDR_RANGE or TS_IPV6_ADDR_RANGE payloads.
ts_ip_src_start: designates the starting value range of source IP
addresses of the inner packet and has the same meaning as the
Starting Address field of the Traffic Selector payload defined in
[RFC7296], Section 3.13.
ts_ip_src_end: designates the high end value range of source IP
addresses of the inner packet and has the same meaning as the
Ending Address field of the Traffic Selector payload defined in
[RFC7296], Section 3.13.
ts_port_src_start: designates the starting value of the port range
of the inner packet and has the same meaning as the Start Port
field of the Traffic Selector payload defined in [RFC7296],
Section 3.13.
ts_port_src_end: designates the starting value of the port range of
the inner packet and has the same meaning as the End Port field of
the Traffic Selector payload defined in [RFC7296], Section 3.13.
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IP addresses and ports are defined as a range and compressed using
the LSB. For a range defined by start and end values, msb( start,
end ) is defined as the function that returns the MSB that remains
unchanged while the value evolves between start and end. Similarly,
lsb( start, end ) is defined as the function that returns the LSB
that changes while the value evolves between start and end. Finally,
len( x ) is defined as the function that returns the number of bits
of the bit array x.
ts_proto: designates the list of Protocol ID field, whose meaning is
defined in [RFC7296], Section 3.13. This profile considers the
specific protocols values "TCP", "UDP", "UDP-Lite", "SCTP" and
"ANY". "ANY" designates any possible values as defined in
[RFC5996], Section 3.13.
dscp_list: designates the list of DSCP values with the same meaning
as the List of DSCP Values defined in [I-D.mglt-ipsecme-dscp-np].
These are not Traffic Selectors, but the compression mandates that
the packets take one of these listed DSCP values.
alignment: indicates the byte alignement supported by the OS for the
ESP extension. By default, the alignment is 32 bit for IPv6, but
some systems may also support an 8 bit alignment. Note that when
a block cipher such as AES-CCM is used, a 128 bit alignment is
overwritten by the block size.
ipsec_mode: designates the IPsec mode defined in [RFC4301]. In this
document, the possible values are "tunnel" for the Tunnel mode and
"transport" for the Transport mode.
tunnel_ip: designates the IP address of the tunnel defined in
[RFC4301]. This field is only applicable when the Tunnel mode is
used. That IP address can be an IPv4 or IPv6 address.
esp_encr: designates the encryption algorithm used. For the purpose
of compression it is RECOMMENDED to use algorithms that already
compresse their IV [RFC8750].
esp_spi: designates the Security Policy Index defined in [RFC4301].
esp_spi_lsb: designates the LSB to be considered for the compressed
SPI. A value of 32 for esp_spi_lsb will leave the SPI unchanged.
esp_sn: designates the Sequence Number (SN) field defined in
[RFC4301].
esp_sn_lsb: designates the LSB to be considered for the compressed
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SN and is defined by this specification. It works similarly to
esp_spi_lsb.
4.3.1. Compression/Decompression Actions in Diet-ESP
In addition to the Compression/Decompression Actions (CDAs) defined
in [RFC8724], Section 7.4, this specification uses the CDAs presented
in Table 2. These CDAs are either a refinement of the compute- * CDA
or the result of a combined CDA.
+========================+=============+======================+
| Action | Compression | Decompression |
+========================+=============+======================+
| lower | elided | Get from lower layer |
+------------------------+-------------+----------------------+
| generated (Flow Label) | elided | Compute flow label |
+------------------------+-------------+----------------------+
| checksum | elided | Compute checksum |
+------------------------+-------------+----------------------+
| ESP padding | elided | Compute padding |
+------------------------+-------------+----------------------+
| hop limit | elided | Get from lower layer |
+------------------------+-------------+----------------------+
| SCHC padding | send | Compute padding |
+------------------------+-------------+----------------------+
Table 2: EHCP ESP related parameter
lower: is only used in a Tunnel mode and indicates that the fields
of the inner IP packet header are generated from the corresponding
fields of the Tunnel IP header fields. This CDA can be used for
the DSCP, ECN, and IPv6 Flow Label (resp. IPv4 identification)
fields.
generated: indicates that a brand new Flow Label/Identification
field is generated following [RFC6437], [RFC6864].
checksum: indicates that a checksum is computed accordingly.
Typically, the checksum CDA has a different implementation for
IPv4, UDP, TCP,...
ESP padding: indicates that the ESP padding bytes are generated
accordingly.
hop limit: indicates that the hop limit is derived from the outer
IPv6 header.
SCHC padding: indicates that the SCHC padding bits are generated
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accordingly.
5. SCHC Compression for IPsec in Tunnel mode
5.1. Inner IP Compression (IIPC)
When iipc_profile is set to "uncompress", the packet is uncompressed.
When iipc_profile is set to "diet-esp", IIPC proceeds to the
compression of the inner IP Packet composed of an IP Header and an IP
Payload. The compression of the inner IP Payload is described in
Section 5.1.1.
The IP Header is compressed when ipsec_mode is set to "Tunnel" and
left uncompressed otherwise. ts_ip_version determines how the IPv6
Header (resp. the IPv4 header) is compressed - see Section 5.1.2
(resp. Section 5.1.3).
5.1.1. Inner IP Payload Compression
The compression only affects UDP, UDP-Lite, TCP or SCTP packets and
the type of packet is determined by the IP header.
For UDP, UDP-Lite, TCP and SCTP packets, source ports, destination
ports, and checksums are compressed. For source port (resp.
destination port) only the least significant bits are sent. FL is
set to 16 bits, TV is set to msb( ts_port_src_start, ts_port_src_end
) ( resp. ts_port_dst_start, ts_port_dst_end ), MO is set to "MSB"
and CDA to "LSB". The checksum is elided, FL is set to 16 bits, TV
is not set, MO is set to "ignore" and CDA is set to "checksum". This
may result in decompressing a zero-checksum UDP packet with a valid
checksum, but this has no impact as a valid checksum is universally
accepted.
For UDP or UDP-Lite the length field is elided. FL is set to 16, TV
is not set, MO is set to "ignore".
5.1.2. Inner IPv6 Header Compression
The version field is elided, FL is set to 3, TV is set to
ts_ipversion, MO is set to "equal" and CDA is set to "not-sent".
Traffic Class is composed of the 6 bit DSCP and 2 bit ECN. The
compression of DSCP and ECN are defined independently.
DSCP values are compressed according to the dscp_cda value:
* If dscp_cda is set to "uncompress", the DSCP values are included
in the inner IP header. FL is set to 6 bits, TV is not set, MO is
set to "ignore", CDA is set to "sent-value".
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* If dscp_cda is set to "lower", the DSCP field is elided and its
value is copied from the Tunnel IP header. FL is set to 6 bits,
TV is not set, MO is set to "ignore", CDA is set to "lower".
* If dscp_cda is set to "sa", DSCP is compressed according to the
DSCP values of the SA. If dscp_list contains a single element,
the DSCP is elided, FL is set to 6 bits, TV is set to
dscp_list[0], MO is set to "equal" and CDA is set to "not-sent".
If dscp_list contains more than one DSCP value, FL is set to 6
bits, TV is set to dscp_list, MO is set to "match-mapping" and the
CDA is set to "mapping-sent". For ECN, FL is set to 2 bits, TV is
not set, MO is set to ignore and CDA is set to "value-sent".
ECN values are compressed according to the ecn_cda value:
* If ecn_cda is set to "uncompress", the ECN field is included in
the inner IP header. FL is set to 2 bits, TV is not set, MO is
set to "ignore", CDA is set to "sent-value".
* If ecn_cda is set to "lower", the ECN value is elided and the ECN
value is copied in the outer IP header. FL is set to 2 bits, TV
is not set, MO is set to "ignore", CDA is set to "lower".
Flow label is compressed according to the flow_label_cda value:
* If flow_label_cda is set to "uncompress", the Flow label is
included in the IPv6 Header. FL is set to 20 bits, TV is not set,
MO is set to "ignore", and CDA is set to "sent-value".
* If flow_label_cda is set to "lower", the Flow Label is elided and
read from the outer IP Header (See Section 4.3.1). FL is set to
20 bits, TV is not set, MO is set to "ignore", and CDA is set to
"lower". If the outer IP header is an IPv4 header, only the 16
LSB of the Flow Label are inserted into the IPv4 Header. At the
decompression, the 4 MSB of the Flow Label are set to 0.
* If flow_label_cda is set to "generated", the Flow Label is elided
and the Flow Label is then re-generated at the decompression (See
Section 4.3.1). The resulting Flow Label differs from the initial
value. FL is set to 20, TV is not set, MO is set to "ignore" and
CDA is set to "generated".
* If flow_label_cda is set to "zero", the Flow Label is elided and
set to 0 at decompression. A 0 value indicates no flow label is
present. Fl is set to 20 bits, TV is set to 0, MO is set to
"equal" and CDA is set to "not-sent".
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Payload Length is elided and determined from the Tunnel IP Header
Payload Length as well as the decompressed Payload. FL is set to 16
bits, TV is not set, MO is set to "ignore", CDA is set to "lower".
Next Header is compressed according to ts_proto:
* If ts_proto is the single value 0, Next Header is not compressed.
FL is set to 8 bits, TV is not set, MO is set to "ignore", CDA is
set to "sent-value".
* If ts_proto is a single non zero value, Next Header is compressed.
FL is set to 8 bits, TV is set to ts_proto, MO is set to "equal"
and CDA is set to "not-sent".
The IPv6 Hop Limit is read from the Tunnel IP Header Hop Limit. FL
is set to 8 bits, TV is not set, MO is set to "ignore" and CDA is set
to "lower."
The source and destination IPv6 addresses are compressed using MSB.
In both cases, FL is set to 128, TV is respectively set to
msb(ts_ip_src_start, ts_ip_src_ed) or msb(ts_ip_dst_start,
ts_ip_dst_end), the MO is set to "MSB," and the CDA is set to "LSB."
5.1.3. Inner IPv4 Header Compression
The fields Version, DSCP, ECN, Source Address and Destination Address
are compressed as described for IPv6 in Section 5.1.2. The field
Total Length (16 bits) is compressed similarly to the IPv6 field
Payload Length. The field Identification (16 bits) is compressed
similarly to the IPv6 field Flow Label. If the IP Header is an IPv6
Header, the Identification is placed as the LSB of the IPv6 Header
and the 4 remaining MSB are set to 0. The field Time to Live is
compressed similarly to the IPv6 Hop Limit field. The Protocol field
is compressed similarly to the last IPv6 Next Header field.
IHL is uncompressed, FL is set to 4 bits, TV is not set, MO is set to
ignore and CDA is set to "value-sent".
The IPv4 Header checksum is elided. FL is set to 16, TV is omitted,
MO is set to "ignore," and CDA is set to "checksum."
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5.2. ESP Data Byte alignment
SCHC operates on bits, while protocols like ESP expect payloads to be
aligned to byte boundaries (8-bit alignment). To ensure this, we
apply a padding by appending the SCHC_padding bits and the
SCHC_padding_len. SCHC_padding_len is encoded over 3 bits to encode
the values 0-7. SCHC_padding is randomly generated. Let's call the
complementing bits, the bits that are needed to have a byte boundary.
If the complementing bits are less than or equal to 2 bits, the
padding will result in adding an extra byte.
5.3. Clear Text ESP Compression (CTEC)
The Clear Text ESP Compression is applied to compress the unencrypted
ESP fields, including the ESP Payload Data and the Next Header field,
which indicates the type of the inner packet.
SCHC Compression efficiently compresses the Next Header field,
reducing overhead and aligning the packet to byte boundaries using
SCHC Padding. After this, the SCHC Pad Length field is added. If
required by the encryption algorithm, additional ESP Padding and Pad
Length fields are introduced to ensure the packet fits the specified
encryption block size.
In tunnel mode, the Next Header field is elided as the inner IP
packet (either IPv4 or IPv6) is determined by the Traffic Selector,
which is expressed by a single Traffic Selector Payload in the SA.
The ESP Padding and Pad Length fields are reduced by the SCHC
compression rule. This process minimizes the size of the Clear Text
ESP packet by eliminating unnecessary padding, while maintaining
proper alignment for transmission. The ESP Padding and Pad Length
may differ from the decompressed versions due to alignment
requirements, which depend on the maximum of the encryption block
alignment or the IPv6 Header alignment (32 bits). Since the padding
is stripped by the IPsec process, these differences do not impact
packet processing. This is expressed as FL is defined by the type
that is to (Pad Length + 1 ) * 8 bits, TV is unset, MO is set to
"ignore" and CDA is set to padding.
5.4. Encrypted ESP Compression (EEC)
SPI is compressed to its LSB. FL is set to 32 bits, TV is not set,
MO is set to "MSB( 4 - esp_spi_lsb)" and CDA is set to "LSB".
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If the esp_encr considers implicit IV [RFC8750], Sequence Numbers are
not compressed. Otherwise, SN are compressed to their LSB similarly
to the SPI. FL is set to 32 bits, TV is not set, MO is set to "MSB(
4 - esp_spi_lsb)" and CDA is set to "LSB".
Note that the use of implicit IV always results in a better
compression as a 64 bit IV to be sent while compression of the SN
alone results at best in a reduction of 32 bits.
The IPv6 Next Header field or the IPv4 Protocol field that contains
the "ESP" value is changed to "SCHC".
6. SCHC Compression for IPsec in Transport mode
The transport mode mostly differs from the Tunnel mode in that the IP
header of the packet is not encrypted. As a result, the IP Payload
is compressed as described in Section 5.1.1. The IP header is not
compressed. The byte alignment of the Compressed Payload is
performed as described in Section 5.2. The Clear Text ESP
Compression is performed as described in Section 5.3 except for the
Next Header Field, which is compressed as described in Section 5.1.2.
7. IANA Considerations
We request the IANA to create a new registry for the IIPC Profile
| IIPC Profile value | Reference |
+--------------------+-----------+
| "uncompress" | ThisRFC |
| "diet-esp" | ThisRFC |
We request IANA to create the following registries for the "diet-esp"
IIPC Profile.
| Flow Label CDA Value | Reference |
+----------------------+-----------+
| "uncompress" | ThisRFC |
| "generated" | ThisRFC |
| "lower" | ThisRFC |
| "zero" | ThisRFC |
| DSCP CDA Value | Reference |
+----------------------+-----------+
| "uncompress" | ThisRFC |
| "lower" | ThisRFC |
| "sa" | ThisRFC |
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| ECN CDA Value | Reference |
+----------------------+-----------+
| "uncompress" | ThisRFC |
| "lower" | ThisRFC |
| Alignment | Reference |
+----------------------+-----------+
| "8 bit" | ThisRFC |
| "16 bit" | ThisRFC |
| "32 bit" | ThisRFC |
| "64 bit" | ThisRFC |
| IPsec mode Value | Reference |
+----------------------+-----------+
| "Tunnel" | ThisRFC |
| "Transport" | ThisRFC |
8. Security Considerations
There are no specific considerations associated with the profile
other than the security considerations of ESP [RFC4303] and those of
SCHC [RFC8724].
9. Acknowledgements
We would like to thank Laurent Toutain for his guidance on SCHC.
Robert Moskowitz for inspiring the name "Diet-ESP" from Diet-HIP.
The authors would like to acknowledge the support from Mitacs through
the Mitacs Accelerate program.
10. References
10.1. Normative References
[I-D.ietf-ipsecme-ikev2-diet-esp-extension]
Migault, D., Guggemos, T., Schinazi, D., Atwood, J. W.,
Liu, D., Preda, S., Hatami, M., and S. Céspedes, "Internet
Key Exchange version 2 (IKEv2) extension for Header
Compression Profile (HCP)", Work in Progress, Internet-
Draft, draft-ietf-ipsecme-ikev2-diet-esp-extension-02, 21
November 2024,
<https://datatracker.ietf.org/api/v1/doc/document/draft-
ietf-ipsecme-ikev2-diet-esp-extension/>.
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[I-D.ietf-schc-architecture]
Pelov, A., Thubert, P., and A. Minaburo, "Static Context
Header Compression (SCHC) Architecture", Work in Progress,
Internet-Draft, draft-ietf-schc-architecture-02, 11 April
2024, <https://datatracker.ietf.org/doc/html/draft-ietf-
schc-architecture-02>.
[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>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <https://www.rfc-editor.org/info/rfc4301>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, DOI 10.17487/RFC5996, September 2010,
<https://www.rfc-editor.org/info/rfc5996>.
[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437,
DOI 10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6864] Touch, J., "Updated Specification of the IPv4 ID Field",
RFC 6864, DOI 10.17487/RFC6864, February 2013,
<https://www.rfc-editor.org/info/rfc6864>.
[RFC7296] Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
Kivinen, "Internet Key Exchange Protocol Version 2
(IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
2014, <https://www.rfc-editor.org/info/rfc7296>.
[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>.
[RFC8376] Farrell, S., Ed., "Low-Power Wide Area Network (LPWAN)
Overview", RFC 8376, DOI 10.17487/RFC8376, May 2018,
<https://www.rfc-editor.org/info/rfc8376>.
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[RFC8724] Minaburo, A., Toutain, L., Gomez, C., Barthel, D., and JC.
Zuniga, "SCHC: Generic Framework for Static Context Header
Compression and Fragmentation", RFC 8724,
DOI 10.17487/RFC8724, April 2020,
<https://www.rfc-editor.org/info/rfc8724>.
[RFC8750] Migault, D., Guggemos, T., and Y. Nir, "Implicit
Initialization Vector (IV) for Counter-Based Ciphers in
Encapsulating Security Payload (ESP)", RFC 8750,
DOI 10.17487/RFC8750, March 2020,
<https://www.rfc-editor.org/info/rfc8750>.
10.2. Informative References
[I-D.mglt-ipsecme-dscp-np]
Migault, D., Halpern, J. M., Parkholm, U., and D. Liu,
"Differentiated Services Field Codepoints Internet Key
Exchange version 2 Notification", Work in Progress,
Internet-Draft, draft-mglt-ipsecme-dscp-np-01, 3 July
2024, <https://datatracker.ietf.org/doc/html/draft-mglt-
ipsecme-dscp-np-01>.
[OpenSCHC] "OpenSCHC a Python open-source implementation of SCHC
(Static Context Header Compression) RFC8724", n.d.,
<https://github.com/openschc>.
[RFC9333] Migault, D. and T. Guggemos, "Minimal IP Encapsulating
Security Payload (ESP)", RFC 9333, DOI 10.17487/RFC9333,
January 2023, <https://www.rfc-editor.org/info/rfc9333>.
Appendix A. Appendix
This appendix provides the details of the SCHC rules defined for
Diet-ESP compression, alongside an explanation and an example
outcome.
A.1. JSON Representation of SCHC Rules for Diet-ESP Header Compression
The JSON file defines a set of rules within the SCHC_Context that are
used for compressing and decompressing ESP headers. Each rule has a
RuleID, a Description, and a set of Fields. Each field specifies how
a particular part of the packet should be handled during compression
or decompression. Note that the RuleID can be set by the user in any
numeric order. The rules include all the compression_levels,
including IIPC, CTEC, and EEC as defined in the Terminology section.
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[
{
"RuleIDValue": 1,
"RuleIDLength": 8,
"Compression": [
{
"FID": "ESP.SPI",
"TV": 5,
"MO": "equal",
"CDA": "not-sent"
},
{
"FID": "ESP.SEQ",
"TV": 1,
"MO": "MSB",
"MO.VAL": 16,
"CDA": "LSB"
}
]
},
{
"RuleIDValue": 2,
"RuleIDLength": 8,
"Compression": [
{
"FID": "UDP.DEV_PORT",
"TV": 123,
"MO": "MSB",
"MO.VAL": 12,
"CDA": "LSB"
},
{
"FID": "UDP.APP_PORT",
"TV": 4567,
"MO": "MSB",
"MO.VAL": 12,
"CDA": "LSB"
},
{
"FID": "UDP.LEN",
"TV": 0,
"MO": "ignore",
"CDA": "compute-length"
},
{
"FID": "UDP.CKSUM",
"TV": 0,
"MO": "ignore",
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"CDA": "compute-checksum"
}
]
},
{
"RuleIDValue": 0,
"RuleIDLength": 0,
"schc_header": [
{
"FID": "SCHC.NXT",
"TV": [17, 50, 41],
"MO": "match-mapping",
"CDA": "mapping-sent"
}
]
},
{
"RuleIDValue": 4,
"RuleIDLength": 8,
"Compression": [
{
"FID": "IPV6.DEV_PREFIX",
"TV": "ff02::5678",
"MO": "equal",
"CDA": "value-sent"
},
{
"FID": "IPV6.APP_PREFIX",
"TV": "2001:db8::1000",
"MO": "equal",
"CDA": "value-sent"
}
]
},
{
"RuleIDValue": 5,
"RuleIDLength": 8,
"Compression": [
{
"FID": "ESP.NXT",
"TV": 41,
"MO": "equal",
"CDA": "not-sent"
}
]
}
]
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A.2. Example Outcome
A.2.1. Input Packet
The following packet undergoes processing based on the SCHC Diet-ESP
profile:
* *IPv6 Header*:
- Source Address: 2001:db8::1000
- Destination Address: ff02::5678
- Other attributes include Payload Length: 18, Next Header: UDP,
and Hop Limit: 64.
* *UDP Header*:
- Source Port: 123
- Destination Port: 4567
- Length: 18
- Checksum: 0x6bc9
* *Payload*:
- 10 bytes sample Data: b'U\xe2(\x88\xbf\xf9\xd91\x08\xc5'
A.2.2. Compression Process
1. *UDP Header Compression*:
* Initial size: 8 bytes.
* Compressed using the UDP-specific rules from the Diet-ESP
profile.
* Ports are encoded as LSB fields, reducing the size to 2 bytes.
2. *IPv6 Header Compression*:
* Initial size: 40 bytes.
* Source and destination addresses are compressed using value-
sent rules based on matching prefixes.
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* Final compressed size: 17 bytes.
3. *ESP Header Compression*:
* Initial size: 12 bytes.
* SPI is not transmitted (not-sent CDA), and SEQ is compressed
using the LSB technique.
* Final compressed size: 2 bytes.
4. *ESP Clear Text Compression*:
* The ESP.NXT field (Next Header) is compressed using the match-
mapping CDA: Rule: The ESP.NXT value is matched to a single
value (41 for the IPv6 Next Header). CDA: mapping-sent is
used to send only the mapped index.
5. *Payload Handling*:
* The payload is not compressed. Further compression may be
possible with additional SCHC rules.
A.2.3. Decompression Process
The decompression reverses the steps:
1. *ESP Header Reconstruction*:
* SPI is restored using the fixed value from the rule (TV=5).
* SEQ is reconstructed from the LSB field.
2. *ESP Clear Text Reconstruction*:
* The ESP.NXT field is restored using the mapping-sent rule,
where the value 41 (Next Header for IPv6) is retrieved from
the mapping.
3. *UDP Header Reconstruction*:
* Ports are restored using the compressed LSB values.
* Length and checksum fields are calculated using compute-length
and compute-checksum CDA.
4. *IPv6 Header Reconstruction*:
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* Prefixes are restored using the value-sent fields in the rule.
5. *Payload Restoration*:
* The payload is directly restored, as it was not compressed.
A.2.4. Final Output Packet
After reconstruction, the packet is identical to the original input:
* *IPv6 Header*:
- Source Address: 2001:db8::1000
- Destination Address: ff02::5678
- Payload Length: 18
- Next Header: UDP
- Hop Limit: 64.
* *UDP Header*:
- Source Port: 123
- Destination Port: 4567
- Length: 18
- Checksum: 0x6bc9.
* *Payload*:
- Data: b'U\xe2(\x88\xbf\xf9\xd91\x08\xc5'.
This example demonstrates the efficiency and accuracy of the Diet-ESP
profile when applied to compress and decompress network packets.
* *Efficiency*: The SCHC rules reduce packet overhead:
- The UDP header is compressed from 8 bytes to 2 bytes.
- The IPv6 header is reduced from 40 bytes to 17 bytes.
- The ESP header size is decreased from 12 bytes to 2 bytes.
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- The ESP.NXT field is eliminated from transmission (1 byte
reduction).
These reductions are particularly beneficial in constrained
environments such as Low-Power Wide-Area Networks (LPWANs).
* *Accuracy*: The decompression process fully reconstructs the
original packet, ensuring no loss of information.
* *Applicability*: By leveraging these rules, the Diet-ESP profile
addresses the challenges of transmitting data efficiently in
constrained networks, optimizing bandwidth utilization while
retaining compatibility with standard protocols.
A.2.5. GitHub Repository: Diet-ESP SCHC Implementation
The source code for the implementation of the Diet-ESP profile,
including the compression and decompression logic using the SCHC
rules, is available on GitHub. Access the code at the following
link:
GitHub Repository: Diet-ESP SCHC Implementation
(https://github.com/mglt/pyesp/tree/master/examples/draft-diet-
esp.py)
This repository contains the rule definitions, examples, and source
code for implementing and testing the Diet-ESP profile. Refer to the
README file for setup instructions and usage guidelines.
Authors' Addresses
Daniel Migault
Ericsson
Email: daniel.migault@ericsson.com
Maryam Hatami
Concordia University
Email: maryam.hatami@mail.concordia.ca
Sandra Céspedes
Concordia University
Email: sandra.cespedes@concordia.ca
J. William Atwood
Concordia University
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Email: william.atwood@concordia.ca
Tobias Guggemos
LMU
Email: guggemos@nm.ifi.lmu.de
Carsten Bormann
Universitaet Bremen TZI
Email: cabo@tzi.org
David Schinazi
Google LLC
Email: dschinazi.ietf@gmail.com
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