ipsecme D. Migault
Internet-Draft Ericsson
Intended status: Standards Track T. Guggemos
Expires: September 12, 2019 LMU Munich
C. Bormann
Universitaet Bremen TZI
D. Schinazi
Google LLC
March 11, 2019
ESP Header Compression and Diet-ESP
draft-mglt-ipsecme-diet-esp-07
Abstract
With the use of encrypted ESP for secure IP communication, the
compression of IP payload is only possible with complex frameworks,
such as RObust Header Compression (ROHC). Such frameworks are too
complex for numerous use cases and especially for IoT scenarios,
which makes IPsec not being used here, although it offers
architectural benefits.
ESP Header Compression (EHC) defines a flexible framework to compress
communications protected with IPsec/ESP. Compression and
decompression is defined by EHC Rules orchestrated by EHC Strategies.
The necessary state is hold within the IPsec Security Association and
can be negotiated during key agreement, e.g. with IKEv2.
The document specifies the necessary parameters of the EHC Context to
allow compression of ESP and the most common included protocols, such
as IPv4, IPv6, UDP and TCP and the corresponding EHC Rules. It also
defines the Diet-ESP EHC Strategy which compresses up to 32 bytes per
packet for traditional IPv6 VPN and up to 66 bytes for IPv6 VPN sent
over a single TCP or UDP session.
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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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 September 12, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 4
5. IPsec Compression Mode . . . . . . . . . . . . . . . . . . . 7
6. EHC Context . . . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. EHC Context Parameters for ESP . . . . . . . . . . . . . 8
6.2. EHC Context Parameters for Inner IP . . . . . . . . . . . 8
6.3. EHC Context Parameters for Transport Protocol . . . . . . 9
7. EHC Rules . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. EHC Rules for ESP . . . . . . . . . . . . . . . . . . . . 13
7.2. EHC Rules for inner IPv4 . . . . . . . . . . . . . . . . 15
7.3. EHC Rules for inner IPv6 . . . . . . . . . . . . . . . . 17
7.4. EHC Rules for UDP . . . . . . . . . . . . . . . . . . . . 18
7.5. EHC Rules for UDP-Lite . . . . . . . . . . . . . . . . . 19
7.6. EHC Rules for TCP . . . . . . . . . . . . . . . . . . . . 20
8. Diet-ESP EHC Strategy . . . . . . . . . . . . . . . . . . . . 21
8.1. Outbound Packet Processing . . . . . . . . . . . . . . . 24
8.2. Inbound Packet Processing . . . . . . . . . . . . . . . . 26
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29
10. Security Considerations . . . . . . . . . . . . . . . . . . . 29
11. Privacy Considerations . . . . . . . . . . . . . . . . . . . 30
12. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . 31
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
13.1. Normative References . . . . . . . . . . . . . . . . . . 31
13.2. Informational References . . . . . . . . . . . . . . . . 32
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Appendix A. Illustrative Examples . . . . . . . . . . . . . . . 33
A.1. Single UDP Session IoT VPN . . . . . . . . . . . . . . . 33
A.2. Single TCP session IoT VPN . . . . . . . . . . . . . . . 36
A.3. Traditional VPN . . . . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 46
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
IPsec/ESP [RFC4303] secures communications either using end-to-end
security or by building a VPN, where the traffic is carried to a
secure domain via a security gateway.
IPsec/ESP was not designed to minimize its associated networking
overhead. In fact, bandwidth optimization often adds computational
overhead that may negatively impact large infrastructures in which
bandwidth usage is not a constraint. On the other hand, in IoT
communications, sending extra bytes can significantly impact the
battery life of devices and thus the life time of the device. The
document describes a framework that optimizes the networking overhead
associated to IPsec/ESP for these devices.
Most compression mechanisms work with dynamic compression contexts.
Some mechanisms, such as ROHC, agree and dynamically change the
context over a dedicated channel. Others, such as 6LowPAN, send the
context together with the actual protocol information in a separate
compression header. Those mechanism fail when it comes to compress
encrypted payloads as appearing in ESP. This is found to be a major
reason, why IPsec and in particular ESP is not widely developed in
environments where bandwidth saving is a critical task, such as in
IoT scenarios.
ESP Header Compression (EHC) chooses another form of context
agreement, which is similar to the one defined by Static Context
Header Compression (SCHC). It works with a static compression
context agreed for a specific Security Association. The context
itself can be negotiated during the key agreement, which allows only
minimal the changes to the actual ESP implementation.
EHC itself is defined as a framework that specifically compresses ESP
protected communications. EHC is highly flexible to address any use
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case where compression is necessary. EHC takes advantage of the
negotiation between the communication endpoint to agree on the
cryptographic parameters, which in some cases already includes
parameters that remain constant during the communications (like layer
4 ports, or IP addresses) and can thus be used as part of the
compression context. Only additional, EHC specific parameters need
to be agreed for the purpose of compression. In addition EHC Rules
define how fields may be compressed and decompressed given the
provided parameters. Finally, EHC defines EHC Strategy which defines
how a set of EHC Rule is coordinated.
This document specifies EHC Context parameters for the most common
Layer 3 and 4 protocols and the associated EHC Rules. Additionally,
an EHC Strategy called Diet-ESP is defined, which compresses up to 32
bytes per packet for traditional VPN and up to 66 bytes for VPN set
over a single TCP or UDP session. Its main purpose is a maximum
level of compression with a minimum of additional agreement. This is
achieved by defining a default usage of existing IPsec SA parameters
wherever possible.
3. Terminology
This document uses the following terminology:
- EHC ESP Header Compression
- IoT Internet of Things
- IP If not stated otherwise, IP means IPv6.
- LSB Least Significant Bytes
- MSB Most Significant Bytes
- SAD IPsec Security Association Database
- SA IPsec Security Association
- SPD IPsec Security Policy Database
- TS IPsec Traffic Selector
- SPI ESP Security Parameter Index
- SN ESP Sequence Number
- PAD ESP Padding
- PL ESP Pad Length
- NH Next Header
- IV Initialization Vector
- IIV Implicit Initialization Vector
- ICV Integrity Check Value
- VPN Virtual Private Network
4. Protocol Overview
ESP Header Compression (EHC) compresses IPsec ESP packets, thus
reducing the size of the packet sent on the wire, while carrying an
equivalent level of information with an equivalent level of security.
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EHC is able to compress any protocol encapsulated in ESP and ESP
itself. Concerned fields include those of the ESP protocol, as well
as other protocols in the ESP payload such as the IP header when the
tunnel mode is used, but also upper layer protocols, such as the UDP
or the TCP header. Non ESP fields may be compressed by ESP under
certain circumstances, but EHC is not intended to provide a generic
way outside of ESP to compress these protocols. Compression of the
unprotected IP header and the unencrypted ESP header may be performed
by mechanism such as 6LoWPAN [RFC4944], SCHC
[I-D.toutain-6lpwa-ipv6-static-context-hc], ROHC [RFC5795] or
6LoWPAN-GHC [RFC7400].
EHC is based on a static compression context, EHC Rules coordinated
by an EHC Strategy:
EHC Context: Stores the information of a specific header field which
can be compressed by EHC. This can be specific header values
such as IP addresses or L4 ports do not have to be send on the
wire at all, or compression information for fields which can be
partially compressed, such as sequence numbers.
EHC Rules: Defines how the information of the EHC Context is used to
compress a specific field. It defines compression functions,
such as "elided", "least significant byte" and others, being
applied on the header field.
EHC Strategy: Is applied to efficiently coordinate EHC Context and
EHC Strategy. The EHC Strategy "Diet-ESP" defined in this
document utilizes the information in the IPsec SA to pre-define
the EHC Context without explicitly exchanging the EHC Context.
As depicted in Figure 1, the EHC Strategy - Diet-ESP in our case -
and the EHC Context are agreed upon between the two peers, e.g.
during key exchange. The EHC Rules are to be implemented on the
peers and do not require further agreement.
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EHC Strategy, EHC Strategy,
EHC Context <==================> EHC Context
| |
EHC Rules | EHC Rules |
| | | |
v v v v
+====================+ +====================+
| ESP | | ESP |
+====================+ +====================+
| < pre-esp > | | < pre-esp > |
+--------------------+ +--------------------+
| < clear text esp > | | < clear text esp > |
+--------------------+ +--------------------+
| < encryption > | | < encryption > |
+--------------------+ +--------------------+
| < post-esp > | | < post-esp > |
+--------------------+ +--------------------+
Figure 1: ESP Header Compression Overview
In Figure 1, the ESP stack is represented by various sub layers
describing the packet processing inside the ESP:
pre-esp: represents treatment performed to a non ESP packet, i.e.
before ESP encapsulation or decapsulation is being performed.
Any compression of protocols not specific to but encrypted by
ESP, such as L4 and higher protocols, is performed here.
clear text esp: designates the ESP encapsulation / decapsulation
processing performed on an non encrypted ESP packet. This layer
includes compression for fields which are included during the ESP
encapsulation. A typical example is the later encrypted Tunnel
IP header and the fields of the ESP trailer.
encryption: designates the encryption/decryption phase This layer
could include compression of encryption information (e.g.
Initialization Vector, etc.), but this is currently out of scope
of this document.
post-esp the processing performed on an ESP encrypted packet. This
layer includes compression of the ESP header.
EHC Rules may be processed at any of these layers and thus impact
differently the standard ESP. More specifically, EHC Rules performed
at the "pre-esp" or "post-esp" layer do not require the current ESP
stack to be updated and can simply be appended to the current ESP
stack. On the other hand, EHC Rules at the "clear text esp" may
require modification of the current ESP stack.
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The set of EHC rules described in this document as well as the EHC
Strategies may be extended in the future. Nothing prevents such EHC
Rules and Strategies to be updated.
5. IPsec Compression Mode
Signalling the compression of a certain ESP packet is crucial for
correct decompression at the sender. Situation where decompression
may fail unforeseen are various, such as IP fragmentation, UDP
options [I-D.ietf-tsvwg-udp-options] just to name a few.
With EHC, the agreement of the level or occurrence of compression is
left the negotiation protocol (e.g. IKEv2), contradicting the
signalization of the level of compression for a certain packet send
over the wire. In order to achieve per-packet signalization of the
compression level, this document proposes new IPsec modes "Compressed
Transport" and "Compressed Tunnel", which are meant to be agreed
during the negotiation of the EHC Contex and EHC Strategy. This
leads to multiple SAs, and thus, multiple SPIs for different levels
of compression agreed with the EHC Context. The receiver can detect
the level of compression of an incoming packet by looking up the used
EHC Context and EHC strategy in the corresponding SA.
If the sender detects the de-compression can not be guaranteed with a
given EHC Context and EHC Strategy, it MUST NOT apply compression.
If an SA with IPsec Mode "Tunnel"/"Transport" is available, the
sender SHOULD send the packet uncompressed, rather than discard the
packet. When there is no uncompressed SA available, the packet MUST
be dropped.
6. EHC Context
The EHC Context provides the necessary information so the two peers
can proceed to the appropriated compression and decompression defined
by the EHC Strategy.
The EHC Context is defined on a per-SA basis. A context can be
defined for any protocol encapsulated with ESP and for ESP itself.
For each header field, a context attribute is provided to the EHC
Context in order to allow compression and decompression. Most power
of EHC lies in the fact, that the attributes for some protocols are
already available in the IPsec SA (e.g. IP addresses in the Traffic
Selector). Such attributes are designated by "Yes" in the "In SA"
column. All others need to be negotiated separately in order to
allow EHC to work properly.
As this document is limited to the Diet-ESP strategy, the EHC Context
in this section used by the Diet-ESP Strategy to activate specific
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EHC Rules as well as to execute the EHC Rules by providing the
necessary parameters..
6.1. EHC Context Parameters for ESP
+-------------------+-------+--------------------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+--------------------------+
| ipsec_mode | Yes | "Tunnel", "Transport" |
| outer_version | Yes | "IPv4", "IPv6" |
| esp_spi | Yes | ESP SPI |
| esp_spi_lsb | No | 0, 1, 2, 3, 4 |
| esp_sn | Yes | ESP Sequence Number |
| esp_sn_lsb | No | 0, 1, 2, 3, 4 |
| esp_sn_gen | No | "Time", "Incremental" |
| esp_align | No | 8, 16, 24, 32 |
| esp_encr | Yes | ESP Encryption Algorithm |
+-------------------+-------+--------------------------+
6.2. EHC Context Parameters for Inner IP
Parameters associated to the Inner IP addresses are only specified
when the SA has been configured with the tunnel mode. As a result
when ipsec_mode is set to "Transport" the parameters below MUST NOT
be considered and are considered as "Undefined"
+-------------------+-------+-----------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+-----------------+
| ip_version | Yes | "IPv4", "IPv6" |
+-------------------+-------+-----------------+
6.2.1. EHC Context Parameters for inner IPv6
+-------------------+-------+------------------------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+------------------------------+
| ip6_tcfl_comp | No | "Outer", "Value", "UnComp" |
| ip6_tc | No | IPv6 Traffic Class |
| ip6_fl | No | IPv6 Flow Label |
| ip6_hl_comp | No | "Outer", "Value", "UnComp" |
| ip6_hl | No | Hop Limit Value |
| ip6_src | Yes | IPv6 Source Address |
| ip6_dst | Yes | IPv6 Destination Address |
+-------------------+-------+------------------------------+
ip6_tcfl_comp indicates how Traffic Class and Flow Label fields of
the inner IP Header are expected to be compressed. "Outer" indicates
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Traffic Class and Flow Label are read from the outer IP header,
"Value" indicates these values are provided by the Diet-ESP Context,
while "Uncompress" indicates that no compression occurs and these
values are read in the inner IP inner header.
ip6_hl_comp indicates how Hop Limit field of the inner IP Header is
expected to be compressed. (see ip6_tcfl_comp).
ip6_dst designates the Destination IPv6 Address of the inner IP
header. The IP address is provided by the TS, and can be defined as
a range of IP addresses. Compression is only considered when ip6_dst
indicates a single IP Address. When the TS defines more than a
single IP address ip6_dst is considered as "Unspecified" and its
value MUST NOT be considered for compression.
6.2.2. EHC Context Parameters for inner IPv4
+-------------------+-------+------------------------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+------------------------------+
| ip4_options | No | "Options", "No_Options" |
| ip4_id | No | IPv4 Identification |
| ip4_id_lsb | No | 0,1,2 |
| ip4_ttl_comp | No | "Outer", "Value", "UnComp" |
| ip4_ttl | No | IPv4 Time To Live |
| ip4_src | Yes | IPv4 Source Address |
| ip4_dst | Yes | IPv4 Destination Address |
| ip4_frag_enable | No | "True", "False" |
+-------------------+-------+------------------------------+
ip4_options specifies if the IPv4 header contains any options. If
set to "No_Options", the first 8 bit of the IPv4 header (being the IP
version and IP header length) are compressed. If set to "Options"
this bits are sent uncompressed.
ip4_ttl indicates how the Time To Live field of the inner IP Header
is expected to be compressed. (see ip6_hl_comp).
6.3. EHC Context Parameters for Transport Protocol
The following parameters are provided by the SA but the SA may
specify single value or a range of values. When the SA specifies a
range of values, these parameters MUST NOT be considered and are
considered as Unspecified.
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+-------------------+-------+------------------------------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+------------------------------------+
| l4_proto | Yes | IPv6/ESP Next Header,IPv4 Protocol |
| l4_src | Yes | UDP/UDP-Lite/TCP Source Port |
| l4_dst | Yes | UDP/UDP-Lite/TCP Destination Port |
+-------------------+-------+------------------------------------+
6.3.1. EHC Context Parameters for UDP
For UDP, there are no additional parameters necessary than the ones
in Section 6.3
6.3.2. EHC Context Parameters for UDP-Lite
+-------------------+-------+----------------------------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+----------------------------------+
| udplite_coverage | No | 8-6535, "Length", "uncompressed" |
+-------------------+-------+----------------------------------+
udplite_coverage: For UDP-Lite, the checksum can have different
coverages, which is defined by the "Checksum Coverage" field which
replaces the "Length" field of UDP. This context field defines the
coverage in advance by either a specific value (8-16535), the actual
length of the UDP-Lite payload ("Length" or 0) or as uncompressed.
Note that udplite coverage is indicated on a packet basis and cannot
be greater than the UDP length. In this case udplite_coverage is
negotiated for all packets and the actual coverage for a given UDP
packet is derived as the minimum value between udplite_coverage and
the length of the UDP packet.
6.3.3. EHC Context Parameters for TCP
+-------------------+-------+---------------------------+
| Context Attribute | In SA | Possible Values |
+-------------------+-------+---------------------------+
| tcp_sn | No | TCP Sequence Number |
| tcp_ack | No | TCP Acknowledgment Number |
| tcp_lsb | No | 0, 1, 2, 3, 4 |
| tcp_options | No | "True", "False" |
| tcp_urgent | No | "True", "False" |
+-------------------+-------+---------------------------+
tcp_sn holds the current Sequence Number of the TCP session.
tcp_ack holds the current Acknowledgement Number of the TCP session.
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tcp_lsb holds the number of lsb of tcp_sn and tcp_ack sent on the
wire.
tcp_options says if options are enabled in the current TCP session.
If tcp_options is set to "False" the Options field in TCP can be
elided.
tcp_urgent says if the urgent pointer is enabled in the current TCP
session. If tcp_urgent is set to "False" the Urgent Pointer field in
TCP can be elided.
7. EHC Rules
This section describes the EHC Rules involved in Diet-ESP. The EHC
Rules defined by Diet-ESP may be used in the future by EHC Strategies
other than Diet-ESP, so they are described in an independent way.
A EHC Rule defines the compression and decompression of one or more
fields and EHC Rules are represented this way:
+---------------+-------+---------+----------------+
| EHC Rule | Field | Action | Parameters |
+---------------+-------+---------+----------------+
| | f1 | a1 | p1_1, ... p1_n |
| +-------+---------+----------------+
| EHC_RULE_NAME ~ ... ~
| +-------+---------+----------------+
| | fm | am | pm_1, ... pm_n |
+---------------+-------+---------+----------------+
Figure 2: EHC Rules
The EHC Rule is designated by a name (EHC_RULE_NAME) and the
concerned Fields (f1, ..., fm). Each field compression and
decompression is represented by an Action (a1, ..., am). The
Parameters indicate the necessary parameters for the action to
perform both the compression and the decompression.
The table below provides a high level description of the Actions used
by Diet-ESP. As these Action may take different arguments and may
operate differently for each field a compete description is provided
in the next sections as part of the EHC Rule description.
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+-----------------+-----------------+----------------------+
| Function | Compression | Decompression |
+-----------------+-----------------+----------------------+
| send-value | No | No |
| elided | Not send | Get from EHC Context |
| lsb(_lsb_size) | Sent LSB | Get from EHC Context |
| lower | Not send | Get from lower layer |
| checksum | Not send | Compute checksum. |
| padding(_align) | Compute padding | Get padding |
+-----------------+-----------------+----------------------+
a. send-value designates an action that does not perform any
compression or decompression of a field.
b. elided designates an action where both peers have a local value
of the field. The compression of the field consists in removing
the field, and the decompression consists in retrieving the field
value from a known local value. The local value may be stored in
a EHC Context or defined by the EHC Rule (like a zero value for
example).
c. lsb designates an action where both peers have a local value of
the field, but the compression consists in sending only the LSB
bytes instead of the whole field. The decompression consists in
retrieving the field from the LSB sent as well as some other
additional local values.
d. lower designates an action where the compression consists in not
sending the field. The decompression consists in retrieving the
field from the lower layers of the packet. A typical example is
when both IP and UDP carry the length of the payload, then the
length of the UDP payload can be inferred from the one of the IP
layer.
e. checksum designates an action where the compression consists in
not sending a checksum field. The decompression consists in re-
computing the checksum. ESP provides an integrity-check based on
signature of the ESP payload (ICV). This makes removing checksum
possible, without harming the checksum mechanism.
f. padding designates an action that computes the padding of the ESP
packet. The function is specific to the ESP.
For all actions, the function can be performed only when the
appropriated parameters and fields are provided. When a field or a
parameters does not have an appropriated value its value is
designated as "Unspecified". Specifically some fields such as inner
IP addresses, ports or transport protocols are agreed during the SA
negotiation and are specified by the SA. Their value in the SA may
take various values that are not appropriated to enable a
compression. For example, when these fields are defined as a range
of values, or by selectors such as OPAQUE or ANY these fields cannot
be retrieved from a local value. Instead, when they are defined as a
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"Single" value (i.e a single IP address, or a single port number or a
single transport protocol number) compression and decompression can
be performed. These SA related fields are considered as
"Unspecified" when not limited to a "Single" value.
When a field or a parameter is "Unspecified", the EHC Rule MUST NOT
be activated. This is the purpose of the EHC Strategy to avoid
ending in such case. In any case, when one of these condition is not
met, the EHC Rule MUST NOT perform any compression or decompression
action and the packet MUST be discarded. When possible, an error
SHOULD be raised and logged.
7.1. EHC Rules for ESP
This section describes the EHC Rules for ESP which are summed up in
the table below.
+---------+-------------------+---------+---------------------------+
| EHC | Field | Action | Parameters |
| Rule | | | |
+---------+-------------------+---------+---------------------------+
| ESP_SPI | SPI | lsb | esp_spi_lsb, esp_spi |
| ESP_SN | Sequence Number | lsb | esp_sn_lsb, esp_sn_gen, |
| | | | esp_sn |
| ESP_NH | Next Header | elided | l4_proto, ipsec_mode |
| ESP_PAD | Pad Length, | padding | esp_align, esp_encr |
| | Padding | | |
+---------+-------------------+---------+---------------------------+
ESP_SPI designates the EHC Rule compressing / decompressing the SPI.
ESP_SPI is performed in the "post-esp" phase. The SPI is compressed
using "lsb". The sending peer only places the LSB bytes of the SPI
and the receiving peer retrieve the SPI from the LSB bytes carried in
the packets as well as from the SPI value stored in the SA. The SPI
MUST be retrieved as its full value is included in the signature
check. The two peers MUST agree on the number of LSB bytes to be
sent: "esp_spi_lsb". Upon agreeing on "esp_spi_lsb", the receiving
peer MUST NOT agree on a value not carrying sufficient information to
retrieve the full SPI.
ESP_SN designates the EHC Rule compressing / decompressing the ESP
Sequence Number. ESP_SN is performed in the "post-esp" phase.
ESP_SN is only activated if the SN ("esp_sn"), the LSB significant
bytes ("esp_sn_lsb") and the method used to generate the SN
("esp_sn_gen") are defined. The Sequence Number is compressed using
"lsb". Similarly to the SPI, the Sequence Number MUST be retrieved
in order to complete the signature check of the ESP packet. Unlike
the SPI, the Sequence Number is not agreed by the peers, but is
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changing for every packet. As a result, in order to retrieve the
Sequence Number from the LSB "esp_sn_lsb", the peers MUST agree on
generating Sequence Number in a similar way. This is negotiated with
"esp_sn_gen" and the receiver MUST ensure that "esp_sn_lsb" is big
enough to absorb minor packet losses or time differences between the
peers.
ESP_NH designates the EHC Rule compressing / decompressing the ESP
Next Header. ESP_NH is performed in the "clear text esp" phase.
ESP_NH is only activated if the Next Header is specified. The Next
Header can be specified as IP (IPv4 or IPv6) when the IPsec tunnel
mode is used ("ipsec_mode" set to "Tunnel") or when the transport
mode ("ipsec_mode" set to "Transport") is used when the Traffic
Selector defines a "Single" Protocol ID ("l4_proto"). The Next
Header, is compressed using "elided". The Next Header indicates the
Header in the Payload Data. When the Tunnel mode is chosen, the type
of the header is known to be an IP header. Similarly, the TS may
also hold transport layer protocol, which specifies the Next Header
value for Transport mode. The Next Header value is only there to
provide sufficient information for decapsulating ESP. In other words
decompressing this fields would occur in the "clear text esp" phase
and striped but directly removed again by the ESP stack. For these
reasons, implementation may simply omit decompressing this field.
ESP_PAD designates the EHC Rule compressing / decompressing the Pad
Length and Padding fields. ESP_PAD is performed in the "clear text
esp" phase. Pad Length and Padding define the padding. The purpose
of padding is to respect a 32 bit alignment for ESP or block sizes of
the used cryptographic suite. As the ESP trailer is encrypted,
Padding and Pad Length MUST to be performed by ESP and not by the
encryption algorithm. Thus, ESP_PAD always needs to respect the
cipher alignment ("esp_encr"), if applicable. Compression may be
performed especially when device support alignment smaller than 32
bit. Such alignment is designated as "esp_align" and the padding
bytes are the necessary bytes so the ESP packet has a length that is
a multiple of "esp_align".
When "esp_align" is set to an 8-bit alignment padding bytes are not
necessary, and Padding as well as Pad Length are removed. For values
that are different from 8-bit alignment, padding bytes needs to be
computed according to the ESP packet length why ESP_PAD MUST be the
last action of "clear text esp". The resulting number of padding
byte is then expressed in Padding and Pad Length fields with Pad
Length set to padding bytes number - 1 and Padding is generated as
described in [RFC4303].
Combining the Pad Length and Padding fields could potentially add an
overhead on fixed size padding. In fact some applications may only
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send the same type of fixed size data, in which case the Pad Length
would not be necessary to be specified. However, the only corner
case Pad Length fields would actually add an overhead is when padding
is expected to be of zero size. In this case, specifying an 8-bit
alignment solve this issue.
7.2. EHC Rules for inner IPv4
All IPv4 EHC Rules MUST be performed during the "clear text esp"
phase. The EHC Rules are only defined for compressing the inner IPv4
header and thus can only be used when the SA is using the Tunnel
mode.
+---------------+-----------------+----------+--------------------+
| EHC Rule | Field | Action | Parameters |
+---------------+-----------------+----------+--------------------+
| IP4_OPT_DIS | Version | elided | ip_version |
| | Header Length | elided | |
| IP4_LENGTH | Total Length | lower | |
| IP4_ID | Identification | lsb | ip4_id, ip4_id_lsb |
| IP4_FRAG_DIS | Flags | elided | |
| | Fragment Offset | elided | |
| IP4_TTL_OUTER | Time To Live | elided | ip4_ttl |
| IP4_TTL_VALUE | Time To Live | elided | ip4_ttl |
| IP4_PROT | Protocol | elided | l4_proto |
| IP4_CHECK | Header Checksum | checksum | |
| IP4_SRC | Source Address | elided | ip4_src |
| IP4_DST | Dest. Address | elided | ip4_dst |
+---------------+-----------------+----------+--------------------+
IP4_OPT_DIS designates that the IPv4 header does not include any
options and indicates if the first byte of the IPv4 header -
consisting of IP version and IPv4 Header Length, are compressed. The
Version "ip_version" is defined by the SA and is thus compressed
using "elided". If the header does not contain any options, it is
compressed with "elided" and decompressed to "20", the default length
of the IPv4 header. If the header does contains some options, the
length is not compressed.
IP4_LENGTH designates the EHC Rule compressing / decompressing the
Total Length Field of the inner IPv4 header. The Total Length is
compressed by the sender and not sent. The receiver decompresses it
by recomputing the Total Length from the outer IP header. The outer
IP header can be IPv4 or IPv6 and IP4_LENGTH MUST support both
versions if both versions are supported by the device. Note that the
length of the inner IP payload may also be subject to updates if
decompression of the upper layers occurs.
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IP4_ID designates the EHC Rule compressing / decompressing the
Identification Field. IP4_ID is only activated if the ID ("ip4_id"),
the LSB significant bytes ("ip4_id_lsb") are defined. Upon agreeing
on "ip4_id_lsb", the receiving peer MUST NOT agree on a value not
carrying sufficient information to retrieve the full IP
Identification. Note also that unlike the ESP SN, the IPv4
Identification is not part of the SA. As a result, when the ID is
compressed, its value MUST be stored in the EHC Context. The
reserved attribute for that is "ip4_id"
IP4_FRAG_DIS designates that the inner IPv4 header does not support
fragmentation. If activated, IP4_FRAG_DIS indicates compression of
Flags and Fragment Offset field in the IPv4 header which consists of
2 bytes. Both fields are compressed with "elided" and decompressed
with their default value according to [RFC0791], which is 0b010 for
Flags and 0 for Fragment Offset.
IP4_TTL_OUTER designates an EHC Rule compressing / decompressing the
Time To Live field of the inner IP header. If the outer IP header is
an IPv6 header, the Hop Limit is used for decompression. The Time To
Live field is compressed / decompressed using "lower", thus the field
is not sent. The receiver decompresses it by reading its value from
the outer IP header (TTL in case of IPv4 or HL in case of IPv6).
IP4_TTL_VALUE designates an EHC Rule compressing / decompressing the
Time To Live field of the inner IP header. IP4_TTL_VALUE is only
activated when the Hop Limit ("ip4_ttl") has been agreed. Time To
Live is compressed / decompressed using the "elided" method.
IP4_PROTO designates the EHC Rule compressing / decompressing the
Protocol field of the inner IPv4 header. IP4_PROTO is only activated
if the Protocol is specified, that is when the Traffic Selectors
defines a "Single" Protocol ID ("l4_proto"). When the Protocol ID
identified by the SA has a "Single" value, the Protocol is compressed
and decompressed using the "elided" method.
IP4_CHECK designates the EHC rule compressing / decompressing the
Header Checksum field of the inner IPv4 header. The IPv4 header
checksum is not sent by the sender and the receiver computes from the
decompressed inner IPv4 header. IP4_CHECK MUST compute the checksum
and not fill the checksum field with zeros. As a result, IP4_CHECK
is the last decompressing EHC Rule to be performed on the
decompressed IPv4 header.
IP4_SRC compresses the source IP address of the inner IPv4 header.
IP4_SRC_IP is only be activated when the Traffic Selectors agreed by
the SA defines a "Single" source IP address ("ip4_src"). The Source
IP address is compressed / decompressed using the "elided" method.
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IP4_DST works in a similar way as IP4_SRC_IP but for the destination
IP address ("ip4_dst")
7.3. EHC Rules for inner IPv6
All IPv6 EHC Rules MUST be performed during the "clear text esp"
phase. The EHC Rules are only defined for compressing the inner IPv6
header and thus can only be used when the SA is using the Tunnel
mode.
+--------------+----------------+--------+------------+
| EHC Rule | Field | Action | Parameters |
+--------------+----------------+--------+------------+
| IP6_OUTER | Version | elided | ip_version |
| | Traffic Class | lower | |
| | Flow Label | lower | |
| IP6_VALUE | Version | elided | ip_version |
| | Traffic Class | elided | ip6_tc |
| | Flow Label | elided | ip6_fl |
| IP6_LENGTH | Payload Length | lower | |
| IP6_NH | Next Header | elided | l4_proto |
| IP6_HL_OUTER | Hop Limit | lower | |
| IP6_HL_VALUE | Hop Limit | elided | ip6_hl |
| IP6_SRC | Source Address | elided | ip6_src |
| IP6_DST | Dest. Address | elided | ip6_dst |
+--------------+----------------+--------+------------+
IP6_OUTER designates an EHC Rule for compressing / decompressing the
first 32 bits of the inner IPv6 header formed by the Version, Traffic
Class and Flow Label. IP6_OUTER only proceeds to compression when
both the outer and inner IP header are IPv6 header. When the outer
IP header is an IPv4, the compression is bypassed. Bypassing enables
to proceed to compression of IPv4 and IPv6 traffic in a VPN use case
with a single SA. The Version "ip_version" is defined by the SA and
is thus compressed using "elided". The other parameters Traffic
Class and Flow Label are compressed using "lower". More
specifically, the fields are not sent. The receiver decompresses
them by reading their value from the outer IPv6 header.
IP6_VALUE designates an EHC Rule for compressing / decompressing the
first 32 bits of the inner IPv6 header formed by the Version, Traffic
Class and Flow Label. IP6_VALUE is only activated if the Version of
the inner IP header agreed by the SA is set to "Version 6"
("ip_version" set to "Version 6") and the specific values of the
Traffic Class ("ip6_tc") and the Flow Label ("ip6_fl") are specified.
With IP6_VALUE all fields are compressed and decompressed using
"elided". Version is provided by the SA ("ip_version") while other
fields are explicitly provided (ip6_tc, ip6_fl.
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IP6_LENGTH designates the EHC Rule compressing / decompressing the
Payload Length Field of the inner IPv6 header. The Payload Length is
compressed by the sender and is not sent. The receiver decompress it
by recomputing the Payload Length from the outer IP header. The IP
header can be IPv4 or IPv6 and IP6_LENGTH MUST support both versions
if both versions are supported by the device. Note that the length
of the inner IP payload may also be subject to updates if
decompression of the upper layers occurs.
IP6_NH designates the EHC Rule compressing / decompressing the Next
Header field of the inner IPv6 header. IP6_NH is only activated if
the Next Header is specified, that is when the Traffic Selectors
defines a "Single" Protocol ID ("l4_proto"). When the Protocol ID
identified by the SA has a "Single" value, the Next Header is
compressed and decompressed using the "elided" method.
IP6_HL_OUTER designates an EHC Rule compressing / decompressing the
Hop Limit field of the inner IP header. If the outer IP header is an
IPv4 header, the Time To Live is used for decompression. The Hop
Limit field is compressed / decompressed using the "lower". More
specifically, the fields are not sent. The receiver decompresses
them by reading their value from the outer IPv6 header.
IP6_HL_VALUE designates an EHC Rule compressing / decompressing the
Hop Limit field of the inner IP header. IP6_HL_VALUE is only
activated when the Hop Limit ("ip6_hl") has been agreed. The Hop
Limit is compressed / decompressed using the "elided" method.
IP6_SRC compresses the source IP address of the inner IP header.
IP6_SRC_IP is only be activated when the Traffic Selectors agreed by
the SA defines a "Single" source IP address ("ip6_src"). The Source
IP address is compressed / decompressed using the "elided" method.
IP6_DST works in a similar way as IP6_SRC_IP but for the destination
IP address ("ip6_dst")
7.4. EHC Rules for UDP
All UDP EHC Rules MUST be performed during the "pre-esp" phase. The
EHC Rules are only defined when the Traffic Selectors agreed during
the SA negotiation results in "Single" Protocol ID ("l4_proto") which
is set to UDP (17).
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+------------+--------------+----------+------------+
| EHC Rule | Field | Action | Parameters |
+------------+--------------+----------+------------+
| UDP_SRC | Source Port | elided | l4_source |
| UDP_DST | Dest. Port | elided | l4_dest |
| UDP_LENGTH | Length | lower | |
| UDP_CHECK | UDP Checksum | checksum | |
+------------+--------------+----------+------------+
UDP_SRC designates the EHC Rule that compresses / decompresses the
UDP Source Port. UDP_SRC is only activated when the Source Port
agreed by the SA negotiation ("l4_src") is "Single". The Source Port
is then compressed / decompressed using the "elided" method.
UDP_DST works in a similar way as UDP_SRC but for the Destination
Port ("l4_dst").
UDP_LENGTH designates the EHC Rule compressing / decompressing the
Length Field of the UDP header. The length is compressed by the
sender and is not sent. The receiver decompresses it by recomputing
the Length from the IP address header. The IP address can be IPv4 or
IPv6 and UDP_LENGTH MUST support both versions if both versions are
supported by the device.
UDP_CHECK designates the EHC Rule compressing / decompressing the UDP
Checksum. The UDP Checksum is not sent by the sender and the
receiver computes from the decompressed UDP payload. UDP_CHECK MUST
compute the checksum and not fill the checksum field with zeros. As
a result, UDP_CHECK is the last decompressing EHC Rule to be
performed on the decompressed UDP Payload.
7.5. EHC Rules for UDP-Lite
All UDP-lite EHC Rules MUST be performed during the "pre-esp" phase.
The EHC Rules are only defined when the Traffic Selectors agreed
during the SA negotiation results in a "Single" Protocol ID
("l4_proto") which is set to UDPLite (136).
+-------------------+-----------------+----------+------------------+
| EHC Rule | Field | Action | Parameters |
+-------------------+-----------------+----------+------------------+
| UDP-LITE_SRC | Source Port | elided | l4_source |
| UDP-LITE_DST | Dest. Port | elided | l4_dest |
| UDP-LITE_COVERAGE | Checksum | elided | udplite_coverage |
| | Coverage | | |
| UDP-LITE_CHECK | UDP-Lite | checksum | |
| | Checksum | | |
+-------------------+-----------------+----------+------------------+
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UDP-LITE_SRC works similarly to UDP_SRC
UDP-LITE_DST works similarly to UDP_DST
UDP-LITE_COVERAGE designates the EHC Rule compressing / decompressing
the UDP-Lite Coverage field. UDP-LITE_COVERAGE is only activated
when the Coverage ("udplite_coverage") has been agreed with a valid
value. The Coverage is compressed / decompressed using the "elided"
method.
UDP-LITE_CHECK designates the EHC Rule compressing / decompressing
the UDP-Lite checksum. UDP-LITE_CHECK is only activated if the
Coverage is defined either elided or sent. UDP-LITE_CHECK computes
the checksum using "checksum" according to the uncompressed UDP
packet and the value of the Coverage.
7.6. EHC Rules for TCP
All TCP EHC Rules MUST be performed during the "pre-esp" phase. The
EHC Rules are only defined when the Traffic Selectors agreed during
the SA negotiation results in a"Single" Protocol ID ("l4_proto")
which is set to TCP (6).
+-------------+-----------------------+----------+------------------+
| EHC Rule | Field | Action | Parameters |
+-------------+-----------------------+----------+------------------+
| TCP_SRC | Source Port | elided | l4_source |
| TCP_DST | Dest. Port | elided | l4_dest |
| TCP_SN | Sequence Number | lsb | tcp_sn, tcp_lsb |
| TCP_ACK | Acknowledgment Number | lsb | tcp_ack, tcp_lsb |
| TCP_OPTIONS | Data Offset | elided | tcp_options |
| | Reserved Bits | elided | |
| TCP_CHECK | TCP Checksum | checksum | |
| TCP_URGENT | TCP Urgent Field | elided | tcp_urgent |
+-------------+-----------------------+----------+------------------+
TCP_SRC works similarly to UDP_SRC.
TCP_DST works similarly to UDP_DST.
TCP_SN designates the EHC Rule compressing / decompressing the TCP
Sequence Number. TCP_SN is only activated if the SN ("tcp_sn") and
the LSB significant bytes ("tcp_lsb") are defined. The TCP SN is
compressed using "lsb". The sending peer only places the LSB bytes
of the TCP SN ("tcp_sn") and the receiving peer retrieve the TCP SN
from the LSB bytes carried in the packets as well as from the TCP SN
value stored in EHC Context ("tcp_sn"). The two peers MUST agree on
the number of LSB bytes to be sent: "tcp_lsb". Upon agreeing on
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"tcp_lsb", the receiving peer MUST NOT agree on a value not carrying
sufficient information to retrieve the full TCP SN. Note also that
unlike the ESP SN, the TCP SN is not part of the SA. As a result,
when the SN is compressed, the value of the TCP SN MUST be stored in
the EHC Context. The reserved attribute for that is "tcp_sn"
TCP_ACK designates the EHC Rule compressing / decompressing the TCP
Acknowledgment Number and works similarly to TCP SN. Note that
"tcp_lsb" is agreed for both TCP SN and TCP Acknowledgment.
Similarly the value of the complete TCP Acknowledgment Number MUST be
stored in the "tcp_ack" attribute of the EHC Context.
TCP_OPTIONS designates the EHC Rule compressing / decompressing TCP
options related fields such as Data Offset and Reserved Bits.
TCP_OPTION can only be activated when the TCP Option ("tcp_options")
is defined. When "tcp_options" is set to "False" and indicates there
are no TCP Options, the Data Offsets and Reserved Bits are compressed
/ decompressed using the "elided" method with Data Offset and
Reserved Bits set to zero.
TCP_CHECK designates the EHC Rule compressing / decompressing the TCP
Checksum. TCP_CHECK works similarly as UDP_CHECK.
TCP_URGENT designates the EHC Rule compressing / decompressing the
urgent related information. When "tcp_urgent" is set to "False" and
indicates there are no TCP Urgent related information, the Urgent
Pointer is then "elided" and filled with zeros.
8. Diet-ESP EHC Strategy
From the attributes of the EHC Context, Diet-ESP defined as an EHC
Strategy, which EHC Rules to apply. The EHC Strategy is defined for
outbound packets which compresses the packet as well as for inbound
packet where the decompression occurs.
Diet-ESP results from a compromise between compression efficiency,
ease to configure Diet-ESP and the various use cases considered. In
order to achieve a great simplicity,
o Diet-ESP favors compression methods that required fewer
configuration: For IPv6, ip6_tcfl_comp and ip6_hl_com to "Outer"
so that ip6_tc, ip6_fl and ip6_hl can be derived from the packet.
Similarly, ip4_ttl_comp has is set to "Outer" so ip4_tll can be
derived from the packet.
o Diet-ESP limits compression method to those foreseen as the most
commonly used. As such, esp_sn_gen has been set to "Incremental"
as this is the most common method used to generate SN. The other
method would be "Time".
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o Diet-ESP limits compression to the most foreseen scenarios. IPv4
compression has been limited in favor of IPv6 as constraint
devices have largely adopted IPv6, and the gain versus the
complexity to deploy IPv4 inner IP addresses has not been proved.
As a result some compressions for IPv4 are not considered by DIet-
ESP. This involved compression of the IPv4 options by setting
ip4_options to "No_Options". Similarly IPv4 ID compression has
not been enabled by setting ip4_id and ip4_id_lsb to
"Unspecified".
o Diet-ESP negotiated values shared by different rules such as
tcp_lsb which is shared for TCP ACK as well as for the TCP SN.
o Diet-ESP defines a logic to set the necessary parameters from
those agreed by the standard ESP agreement, which limits the
setting of parameters.
The following tables shows, which EHC Rules are activated by default
for the supported protocols ESP, IPv4, IPv6, UDP, UDP-Lite and TCP
when using the Diet-ESP strategy and which ones are activated due to
certain circumstances or explicit negotiation
ESP:
+----------+--------------+-------------+------------+
| EHC Rule | Activated if | Parameter | Value |
+----------+--------------+-------------+------------+
| ESP_SPI | Diet-ESP | esp_spi_lsb | Negotiated |
| | | esp_spi | In SA |
| ESP_SN | Diet-ESP | esp_sn_lsb | Negotiated |
| | | esp_sn_gen | Negotiated |
| | | esp_sn | In SA |
| ESP_NH | Diet-ESP | ipsec_mode | In SA |
| | | l4_proto | In SA |
| ESP_PAD | Diet-ESP | esp_align | Negotiated |
| | | esp_encr | In SA |
+----------+--------------+-------------+------------+
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IPv4:
+---------------+---------------+------------+-------+
| EHC Rule | Activated if | Parameter | Value |
+---------------+---------------+------------+-------+
| IP4_OPT_DIS | ip_version==4 | ip_version | In SA |
| IP4_LENGTH | ip_version==4 | None | |
| IP4_FRAG_DIS | ip_version==4 | None | |
| IP4_TTL_OUTER | ip_version==4 | None | |
| IP4_TTL_OUTER | ip_version==4 | l4_proto | In SA |
| IP4_CHECK | ip_version==4 | None | |
| IP4_SRC | ip_version==4 | ip4_src | In SA |
| IP4_DST | ip_version==4 | ip4_dst | In SA |
+---------------+---------------+------------+-------+
IPv6:
+--------------+---------------+------------+-------+
| EHC Rule | Activated if | Parameter | Value |
+--------------+---------------+------------+-------+
| IP6_OUTER | ip_version==6 | ip_version | In SA |
| IP6_LENGTH | ip_version==6 | None | |
| IP6_NH | ip_version==6 | l4_proto | In SA |
| IP6_HL_OUTER | ip_version==6 | None | |
| IP6_SRC | ip_version==6 | ip6_src | In SA |
| IP6_DST | ip_version==6 | ip6_dst | In SA |
+--------------+---------------+------------+-------+
UDP:
+------------+--------------+-----------+-------+
| EHC Rule | Activated if | Parameter | Value |
+------------+--------------+-----------+-------+
| UDP_SRC | l4_proto==17 | l4_source | In SA |
| UDP_DST | l4_proto==17 | l4_dest | In SA |
| UDP_LENGTH | l4_proto==17 | None | |
| UDP_CHECK | l4_proto==17 | None | |
+------------+--------------+-----------+-------+
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UDP-Lite:
+-------------------+---------------+------------------+------------+
| EHC Rule | Activated if | Parameter | Value |
+-------------------+---------------+------------------+------------+
| UDP_LITE_SRC | l4_proto==136 | l4_source | In SA |
| UDP_LITE_DST | l4_proto==136 | l4_dest | In SA |
| UDP_LITE_COVERAGE | l4_proto==136 | udplite_coverage | Negotiated |
| UDP_LITE_CHECK | l4_proto==136 | None | |
+-------------------+---------------+------------------+------------+
TCP:
+-------------+--------------+-------------+------------+
| EHC Rule | Activated if | Parameter | Value |
+-------------+--------------+-------------+------------+
| TCP_SRC | l4_proto==6 | l4_source | In SA |
| TCP_DST | l4_proto==6 | l4_dest | In SA |
| TCP_SN | l4_proto==6 | tcp_sn | In SA |
| | | tcp_lsb | Negotiated |
| TCP_ACK | l4_proto==6 | tcp_ack | In SA |
| | | tcp_lsb | Negotiated |
| TCP_OPTIONS | l4_proto==6 | tcp_options | Negotiated |
| TCP_CHECK | l4_proto==6 | None | |
| TCP_URGENT | l4_proto==6 | tcp_urgent | Negotiated |
+-------------+--------------+-------------+------------+
Thus, the parameters that the two peers needs to agree on are:
o esp_sn_lsb
o esp_spi_lsb
o esp_align
o udplite_coverage
o tcp_lsb
o tcp_options
o tcp_urgent
Implementation may differ from the description below. However, the
outcome MUST remain the same.
8.1. Outbound Packet Processing
Diet-ESP compression is defined as follows:
1. In phase "pre-esp": Match the inbound packet with the SA and
determine if the Diet-ESP EHC Strategy has been activated. If
the Diet-ESP EHC Strategy has been activated proceed to next
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step, otherwise skip all steps associated to Diet-ESP and proceed
to the standard ESP as defined in [RFC4303]
2. In phase "pre-esp": If "l4_proto" designates a "Single" Protocol
ID (UDP, TCP or UDP-Lite), proceed to the compression of the
specific layer. Otherwise, the transport layer is not
compressed.
3. In phase "clear text esp": If "ipsec_mode" is set to "Tunnel"
mode, determine "ip_version" the IP version of the inner IP
addresses and proceed to the appropriated inner IP address
compression.
4. In phase "clear text esp" and "post-esp": Proceed to the ESP
compression.
UDP compression is defined as below:
1. If "l4_src" designates a "Single" Source Port, apply UDP_SRC to
compress the Source Port.
2. If "l4_dst" designates a "Single" Destination Port, apply UDP_DST
to compress the Destination Port.
3. Apply UDP_CHECK to compress the Checksum.
4. Apply UDP_LENGTH to compress the Length.
UDP-lite compression is defined as below:
1. If "l4_src" designates a "Single" Source Port, apply the UDP-
LITE_SRC to compress the Source Port.
2. If "l4_dst" designates a "Single" Destination Port, apply the
UDP-LITE_DST, to compress the Destination Port.
3. If "udplite_coverage" is specified, apply the UDP-LITE_COVERAGE,
to compress the Coverage.
4. Apply UDP-LITE_CHECK to compress the Checksum.
TCP compression is defined as below:
1. If "l4_src" designates a "Single" Source Port than apply the
TCP_SRC to compress the Source Port.
2. If "l4_dst" designates a "Single" Destination Port than apply the
TCP_DST to compress the Destination Port.
3. If "tcp_lsb" is lower than 4, then "tcp_sn" "tcp_ack" attributes
of the Diet-ESP Context are updated with the value provided from
the packet before applying the TCP_SN and the TCP_ACK EHC Rules.
4. If "tcp_options" is set to "False" apply the TCP_OPTIONS EHC
Rule.
5. If "tcp_urgent" is set to "False" apply the TCP_URGENT EHC Rule.
6. Apply TCP_CHECK to compress the Checksum.
Inner IPv6 Header compression is defined as below:
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1. If "ip6_src" designates a "Single" Source IP address, apply the
IP6_SRC to compress the IPv6 Source Address.
2. If "ip6_dst" designates a "Single" Destination IP address, apply
the IP6_DST to decompress the IPv6 Destination Address.
3. Apply IPv6_HL_OUTER to compress the Hop Limit.
4. If "l4_proto" designates a "Single" Protocol ID (UDP, TCP or UDP-
Lite), apply IP6_NH to compress the Next Header.
5. Apply, IP6_LENGTH to compress the Length.
6. Apply IP6_OUTER to compress Version, Traffic Class and Flow
Label.
Inner IPv4 Header compression is defined as below:
1. Apply, IP4_LENGTH to compress the Length.
2. Apply IP4__TTL_OUTER to compress Time To Live.
3. Apply, IP4_CHECK to compress the IPv4 header checksum.
4. If "ip4_src" designates a "Single" Source IP address, apply the
IP4_SRC to compress the IPv4 Source Address.
5. If "ip4_dst" designates a "Single" Destination IP address, apply
the IP4_DST to decompress the IPv4 Destination Address.
ESP compression is defined as below:
1. In phase "clear text esp": If "ipsec_mode" is set to "Tunnel" or
"l4_proto" is set to a "Single value - eventually different from
TCP, UDP or UDP-Lite, apply ESP_NH, to compress the Next Header.
2. In phase "clear text esp": If "esp_encr" specify an encryption
algorithm that does not provide padding, then apply ESP_PAD to
compress the Pad Length and Padding.
3. Proceed to the ESP encryption as defined in [RFC4303].
4. In phase "post-esp: If "esp_sn_lsb" is different from 4, then
apply ESP_SN. To compress the ESP SN.
5. In phase "post-esp": If "esp_spi_lsb" is different from 4, then
apply ESP_SPI to compress the SPI.
8.2. Inbound Packet Processing
Diet-ESP decompression is defined as follows:
1. Match the inbound packet with the SA and determine if the Diet-
ESP EHC Strategy has been activated. When Diet-ESP is activated
this means that the "esp_spi_lsb" are sufficient to index the SA
and proceed to next step, otherwise skip all steps associated to
Diet-ESP and proceed to the standard ESP as defined in [RFC4303]
2. In phase "clear text esp" and "post-esp": Proceed to the ESP
decompression.
3. In phase "clear text esp": If "ipsec_mode" is set to "Tunnel"
mode, determine "ip_version" the IP version of the inner IP
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addresses and proceed to the appropriated inner IP address
decompression, except for the computation of the checksums and
length.
4. In phase "pre-esp": If "l4_proto" designates a "Single" Protocol
ID (UDP, TCP or UDP-Lite), proceed to the decompression of the
specific layer, except for the computation of the checksums and
length replaced by zero fields.
5. In phase "pre-esp": Proceed to the decompression of the checksums
and length.
ESP decompression is defined as follows:
1. In phase "post-esp": If "esp_spi_lsb" is different from 4, then
apply ESP_SPI to decompress the SPI.
2. In phase "post-esp: If "esp_sn_lsb" is different from 4, then
apply ESP_SN. To decompress the ESP SN.
3. Proceed to the ESP signature validation and decryption as defined
in [RFC4303].
4. In phase "clear text esp": If "ipsec_mode" is set to "Tunnel" or
"l4_proto" is set to a "Single value - eventually different from
TCP, UDP or UDP-Lite, apply ESP_NH, to decompress the Next
Header.
5. In phase "clear text esp": If "esp_encr" specify an encryption
algorithm that does not provide padding, then apply ESP_PAD to
compress the Pad Length and Padding.
6. Extract the ESP Data Payload and apply decompression EHC Rule to
the ESP Data Payload.
UDP decompression is defined as follows:
1. If "l4_src" designates a "Single" Source Port, apply UDP_SRC to
decompress the Source Port.
2. If "l4_dst" designates a "Single" Destination Port, apply UDP_DST
to decompress the Destination Port.
3. Apply UDP_LENGTH to compress the Length. The length value is
computed from the length provided by the lower layer, with the
additional added bytes during the UDP decompression including the
length size.
4. Apply UDP_CHECK to decompress the Checksum.
5. Update the Length of the lower layers:
1. If "ipsec_mode" is set to "Transport" mode, update the Length
of the outer IP header (IPv4 or IPv6). The Length is
incremented by the number of bytes generated by the
decompression of the transport layer.
2. If "ipsec_mode" is set to "Tunnel" mode, update the Length of
the inner IP address (IPv4 or IPv6) as well as the outer IP
header (IPv4 or IPv6). The Length is incremented by the
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number of bytes generated by the decompression of the
transport layer.
UDP-Lite decompression is defined as follows:
1. If "l4_src" designates a "Single" Source Port, apply the UDP-
LITE_SRC to decompress the Source Port.
2. If "l4_dst" designates a "Single" Destination Port, apply the
UDP-LITE_DST, to decompress the Destination Port.
3. If "udplite_coverage" is specified, apply the UDP-LITE_COVERAGE,
to decompress the Coverage.
4. Apply UDP-LITE_CHECK to compress the Checksum.
5. Update the Length of the lower layers as defined in UDP.
TCP decompression is defined as follows:
1. If "l4_src" designates a "Single" Source Port than apply the
TCP_SRC to decompress the Source Port.
2. If "l4_dst" designates a "Single" Destination Port than apply the
TCP_DST to decompress the Destination Port.
3. If "tcp_lsb" is lower than 4, apply TCP_SN and the TCP_ACK to
decompress the TCP Sequence Number and the TCP Acknowledgment
Number.
4. If "tcp_options" is set to "False" apply TCP_OPTIONS to
decompress Data Offset and Reserved Bits.
5. If "tcp_urgent" is set to "False" apply the TCP_URGENT to
decompress the Urgent Pointer.
6. Apply TCP_CHECK to decompress the Checksum.
Inner IPv6 decompression is defined as follows:
1. Apply IP6_OUTER to decompress Version, Traffic Class and Flow
Label.
2. Set the Length to zero.
3. If "l4_proto" designates a "Single" Protocol ID (UDP, TCP or UDP-
Lite), apply IP6_NH to decompress the Next Header.
4. Hop Limit is decompressed with IP6_HL_OUTER (with "ip6_hl_comp"
set to "Outer").
5. If the "ip6_src" designates a "Single" Source IP address, apply
the IP6_SRC to de compress the IPv6 Source Address.
6. If the "ip6_dst" designates a "Single" Destination IP address
than apply the IP6_DST to decompress the IPv6 Destination
Address.
7. Apply, IP6_LENGTH to provide the replace the zero length value by
its appropriated appropriated value. The Length value considers
the length provided by the lower layers to which are added the
additional bytes due to the decompression, minus the length of
the inner IP6 Header.
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Inner IPv4 decompression is defined as follows:
1. Apply, IP4_LENGTH to provide the replace the zero length value by
its appropriated appropriated value. The Length value considers
the length provided by the lower layers to which are added the
additional bytes due to the decompression, minus the length of
the inner IPv4 Header. The value computed from the lower layer
will have to be overwritten in case further decompression occurs.
2. Apply IP4_TTL_OUTER to decompress Time To Live.
3. If "l4_proto" designates a "Single" Protocol ID (UDP, TCP or UDP-
Lite), apply IP4_PROT to decompress the Protocol Field.
4. If "ip4_src" designates a "Single" Source IP address, apply the
IP4_SRC to de compress the IPv4 Source Address.
5. If "ip4_dst" designates a "Single" Destination IP address than
apply the IP4_DST to decompress the IPv4 Destination Address.
6. Apply IP4_CHECK to decompress the checksum of the IPv4 header
9. IANA Considerations
There are no IANA consideration for this document.
10. Security Considerations
This section lists security considerations related to the Diet-ESP
protocol.
Security Parameter Index (SPI):
The Security Parameter Index (SPI) is used by the receiver to
index the Security Association that contains appropriated
cryptographic material. If the SPI is not found, the packet is
rejected as no further checks can be performed. In EHC, the value
of the SPI is not reduced, but compressed why the SPI value may
not be fully provided between the compressor and the de-
compressor. On the other hand, its uncompressed value is provided
to the ESP-procession and no weakness is introduced to ESP itself.
On an implementation perspective, it is strongly recommended that
decompression is deterministic. Compression and decompression
adds some additional treatment to the ESP packet, which might be
used by an attacker. In order to minimize the load associated to
decompression, decompression is expected to be deterministic. The
incoming compressed SPI with the associated IP addresses should
output a single and unique uncompressed SPI value. If an
uncompressed SPI values have to be considered, then the receiver
could end in n signature checks which may be used by an attacker
for a DoS attack.
Sequence Numer (SN):
The Sequence Number (SN) is used as an anti-replay attack
mechanism. Compression and decompression of the SN is already
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part of the standard ESP namely the Extended Sequence Number
(ESN). The SN in a standard ESP packet is 32 bit long, whether
EHC enables to reduce it to 0 bytes and the main limitation to the
compression a deterministic decompression. SN compression
consists in indicating the least significant bits of the
uncompressed SN on the wire. The size of the compressed SN must
consider the maximum reordering index such that the probability
that a later sent packet arrives before an earlier one. In
addition the size of SN should also consider maximum consecutive
packets lost during transmission. In the case of ESP, this number
is set to 2^32 which is, in most real world case, largely over-
provisioned. When the compression of the SN is not appropriately
provisioned, the most significant bit value may be de-synchronized
between the sending and receiving parties. Although IKEv2
provides some re-synchronization mechanisms, in case of IoT the
de-synchronization will most likely result in a renegotiation and
thus DoS possibilities. Note that IoT communication may also use
some external parameters, i.e. other than the compressed SN, to
define whether a packet be considered or not and eventually derive
the SN. One such scenario may be the use of time windows.
Suppose a device is expected to send some information every hour
or every week. In this case, for example, the SN may be
compressed to zero bytes. Instead the SN may be derived by
incrementing the SN every hour after the last received valid
packet. Considering the time the packet is received make it
possible to consider the time derivation of the sensor clock. If
TIME is used as the method to generate the SN, the receiver MUST
ensure that the esp_sn_lsb is big enough to resist time
differences between the nodes. Note also that the anti-replay
mechanism needs to define the size of the anti-replay
window.[RFC4303] provides guidance to set the window size and are
similar to those used to define the size of the compressed SN.
11. Privacy Considerations
Security Parameter Index (SPI):
Until Diet-ESP is not deployed outside the scope of IoT and small
devices, the use of a compressed SPI may provide an indication
that one of the endpoint is a sensor. Such information may be
used, for example, to evaluate the number of appliances deployed,
or - in addition with other information, such as the time
interval, the geographic location - be used to derive the type of
data transmitted.
Sequence Number (SN): If incremented for each ESP packet, the SN may
leak some information like the amount of transmitted data or the
age of the sensor. The age of the sensor may be correlated with
the software used and the potential bugs. On the other hand, re-
keying will re-initialize the SN, but the cost of a re-keying may
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not be negligible and thus, frequent re-keying can be considered.
In addition to the re-key operation, the SN may be generated in
order to reduce the accuracy of the information leaked. In fact,
the SN does not have to be incremented by one for each packet it
just has to be an increasing function. Using a function such as a
TIME may prevent characterizing the age or the use of the sensor.
Note that the use of such function may also impact the compression
efficiency and result in larger compressed SN.
12. Acknowledgment
We would like to thank Orange and Universitee Pierre et Marie Curie
for initiating the work on Diet-ESP. We Would like to thank Sylvain
Killian for implementing an open source Diet-ESP on Contiki and
testing it on the FIT IoT-LAB [fit-iot-lab] funded by the French
Ministry of Higher Education and Research. We thank the IoT-Lab Team
and the INRIA for maintaining the FIT IoT-LAB platform and for
providing feed backs in an efficient way.
We would like to thank Bob Moskowitz for not copyrighting Diet HIP.
The "Diet" terminology is from him.
We would like to thank those we received many useful feed backs among
others: Dominique Bartel, Anna Minaburo, Suresh Krishnan, Samita
Chakrabarti, Michael Richarson, Tero Kivinen.
13. References
13.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
DOI 10.17487/RFC0791, September 1981,
<https://www.rfc-editor.org/info/rfc791>.
[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>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<https://www.rfc-editor.org/info/rfc4303>.
[RFC4309] Housley, R., "Using Advanced Encryption Standard (AES) CCM
Mode with IPsec Encapsulating Security Payload (ESP)",
RFC 4309, DOI 10.17487/RFC4309, December 2005,
<https://www.rfc-editor.org/info/rfc4309>.
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[RFC4944] Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
"Transmission of IPv6 Packets over IEEE 802.15.4
Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
<https://www.rfc-editor.org/info/rfc4944>.
[RFC5795] Sandlund, K., Pelletier, G., and L-E. Jonsson, "The RObust
Header Compression (ROHC) Framework", RFC 5795,
DOI 10.17487/RFC5795, March 2010,
<https://www.rfc-editor.org/info/rfc5795>.
[RFC5858] Ertekin, E., Christou, C., and C. Bormann, "IPsec
Extensions to Support Robust Header Compression over
IPsec", RFC 5858, DOI 10.17487/RFC5858, May 2010,
<https://www.rfc-editor.org/info/rfc5858>.
[RFC7400] Bormann, C., "6LoWPAN-GHC: Generic Header Compression for
IPv6 over Low-Power Wireless Personal Area Networks
(6LoWPANs)", RFC 7400, DOI 10.17487/RFC7400, November
2014, <https://www.rfc-editor.org/info/rfc7400>.
[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>.
13.2. Informational References
[I-D.toutain-6lpwa-ipv6-static-context-hc]
Minaburo, A. and L. Toutain, "6LPWA Static Context Header
Compression (SCHC) for IPV6 and UDP", draft-toutain-6lpwa-
ipv6-static-context-hc-01 (work in progress), June 2016.
[I-D.mglt-ipsecme-implicit-iv]
Migault, D., Guggemos, T., and Y. Nir, "Implicit IV for
Counter-based Ciphers in IPsec", draft-mglt-ipsecme-
implicit-iv-04 (work in progress), June 2017.
[I-D.ietf-tsvwg-udp-options]
Touch, J., "Transport Options for UDP", draft-ietf-tsvwg-
udp-options-07 (work in progress), March 2019.
[fit-iot-lab]
"Future Internet of Things (FIT) IoT-LAB",
<https://www.iot-lab.info>.
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Appendix A. Illustrative Examples
A.1. Single UDP Session IoT VPN
This section considers a IoT IPv6 probe hosting a UDP application.
The probe is dedicated to a single application and establishes a
single UDP session. As a result, inner IP addresses and UDP Ports
have a "Single" value and can be easily compressed. The probes sets
an IPsec VPN using IPv6 addresses in order to connect its secure
domain - typically a Home Gateway. The use of IPv6 for inner and
outer IP addresses, enables to infer inner IP fields from the outer
IP address. The probes encrypts with AES-CCM_8 [RFC4309]. AES-CCM
does not have padding, so the padding is performed by ESP. The
probes uses an 8 bit alignment which enables to fully compress the
ESP Trailer. In addition, as the probe SA is indexed using the outer
IP addresses (or eventually the radio identifiers) which enables to
fully compress the SPI. As the probe provides information every
hour, the Sequence Number using time can be derived from the received
time, which enables to fully compress the SN.
Figure 3 represents the original UDP packet and Figure 4 represents
the corresponding packet compressed with Diet-ESP. The compression
with Diet-ESP results in a reduction of 61 bytes overhead. With IPv4
inner IP addressed Diet-ESP results in an 45 byte overhead reduction.
Further compression may be done for example by using an implicit IV
[I-D.mglt-ipsecme-implicit-iv] and by compressing the outer IP
addresses (not represented) on the figure. In addition, application
data may also be compressed with mechanisms outside of the scope of
Diet-ESP.
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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
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
E| Security Parameters Index (SPI) | ^
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
P| Sequence Number (SN) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| IV | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- |
I|version| traffic class | flow label |^ |
P+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
v| payload length | next header | hop limit || |
6+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || a
| inner source IP || u
| |e t
| |n h
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+c e
| |r n
| inner destination IP |y t
| |p i
| |t c
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+e a
U| source port | dest port |d t
D+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| e
P| length | checksum || d
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || |
~ APPLICATION DATA ~| |
| || |
-| +-+-+-+-+-+-+-+-+| |
E| | Padding || |
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
P| Padding (continue) | Pad Length | Next Header |v v
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| Integrity Check Value-ICV (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Standard ESP VPN Packet Description
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
| | ^
| IV | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ aut
| | hen
~ APPLICATION DATA ~ tic
| (encrypted) | ate
| +-+-+-+-+-+-+-+-+ |
| | | V
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |--
| Integrity Check Value-ICV (variable) |
| +-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Diet-ESP Single UDP Session IoT VPN Packet Description
The following table illustrates the activated rules and the
attributes of the Diet-ESP Context that needs an explicit agreement
to achieve the compression. All other attributes used by the rules
are part of the SA agreement. Parameters of not activated rules are
left "Unspecified".
+--------------+-------------------+-------+
| EHC Rule | Context Attribute | Value |
+--------------+-------------------+-------+
| ESP_SPI | esp_spi_lsb | 0 |
| ESP_SN | esp_sn_lsb | 0 |
| | esp_sn_gen | |
| ESP_NH | | |
| ESP_PAD | esp_align | 8 |
| | | |
| IP6_OUTER | ip6_tcfl_comp | |
| | ip6_hl_comp | |
| IP6_LENGTH | | |
| IP6_NH | | |
| IP6_HL_OUTER | | |
| IP6_SRC | | |
| IP6_DST | | |
| | | |
| UDP_SRC | | |
| UDP_DST | | |
| UDP_LENGTH | | |
| UDP_CHECK | | |
+--------------+-------------------+-------+
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A.2. Single TCP session IoT VPN
This section considers the same probe as described in Appendix A.1
but instead of using UDP as a transport layer, the probe uses TCP.
In this case TCP is used with no options, no urgent pointers and the
SN and ACK Number are compressed to 2 bytes as the throughput is
expected to be low.
Figure 5 represents the original TCP packet and Figure 6 represents
the corresponding packet compressed with Diet-ESP. The compression
with Diet-ESP results in a reduction of 66 bytes overhead. With IPv4
inner address Diet-ESP results in a 50 byte overhead reduction.
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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
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
E| Security Parameters Index (SPI) | ^
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
P| Sequence Number (SN) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| IV | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- |
I|version| traffic class | flow label |^ |
P+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
v| payload length | next header | hop limit || |
6+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || a
| inner source IP || u
| |e t
| |n h
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+c e
| |r n
| inner destination IP |y t
| |p i
| |t c
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+e a
T| source port | dest port |d t
C+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| e
P| Sequence Number (SN) || d
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| ACK Sequence Number || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
|Off. | Rserv | Flags | Window Size || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| Checksum | Urgent Pointer || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || |
~ APPLICATION DATA ~| |
| || |
| +-+-+-+-+-+-+-+-+| |
E| | Padding || |
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
P| Padding (continue) | Pad Length | Next Header |V V
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| Integrity Check Value-ICV (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Standard IoT Single TCP Session VPN Packet Description
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---a
| | ^u
| IV | |t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--|h
| Sequence Number (SN) | ACK Sequence Number |^e|e
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|n|n
| Flags | Window Size | ||c|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ||r|i
| ~|y|c
~ APPLICATION DATA ||p|a
| ||t|t
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|e|e
| | |vdvd
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |---
| Integrity Check Value-ICV (variable) |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Diet-ESP Single TCP Session IoT VPN Packet Description
The following table illustrates the activated rules and the
attributes of the Diet-ESP Context that needs an explicit agreement
to achieve the compression. All other attributes used by the rules
are part of the SA agreement. Parameters of not activated rules are
left "Unspecified". Note for simplicity, tcp_sn and tcp_ack are
negotiated to start with 0, but it could be any other value as well.
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+--------------+-------------------+---------+
| EHC Rule | Context Attribute | Value |
+--------------+-------------------+---------+
| ESP_SPI | esp_spi_lsb | 0 |
| ESP_SN | esp_sn_lsb | 0 |
| | esp_sn_gen | |
| ESP_NH | | |
| ESP_PAD | esp_align | 8 |
| | | |
| IP6_OUTER | ip6_tcfl_comp | |
| | ip6_hl_comp | |
| IP6_LENGTH | | |
| IP6_NH | | |
| IP6_HL_OUTER | | |
| IP6_SRC | | |
| IP6_DST | | |
| | | |
| TCP_SRC | | |
| TCP_DST | | |
| TCP_SN | tcp_lsb | 2 |
| | tcp_sn | 0 |
| TCP_ACK | tcp_lsb | 2 |
| | tcp_ack | 0 |
| TCP_OPTIONS | tcp_options | "False" |
| TCP_CHECK | | |
| TCP_URGENT | tcp_urgent | "False" |
+--------------+-------------------+---------+
A.3. Traditional VPN
This section illustrates the case of an company VPN. The VPN is
typically set by a remote host that forwards all its traffic to the
security gateway. As transport protocols are "Unspecified",
compression is limited to ESP and the inner IP header. For the inner
IP header, the Destination IP address is "Unspecified" so the
compression of the inner IP address excludes the Destination IP
address. Similarly, the inner IP Next Header cannot be compressed as
the transport layer is not specified. For ESP, the security gateway
may only have a sufficiently low number of remote users with
relatively low throughput in which case SPI and SN can be compressed
to 2 bytes. As throughput remains relatively low, the alignment may
also set to 8 bits.
A.3.1. IPv6 in IPv6
Figure 7 represents the original TCP packet with IPv6 inner IP
addresses and Figure 8 represents the corresponding packet compressed
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with Diet-ESP. The compression with Diet-ESP results in a reduction
of 32 bytes.
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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
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
E| Security Parameters Index (SPI) | ^
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
P| Sequence Number (SN) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| IV | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- |
I|version| traffic class | flow label |^ |
P+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
v| payload length | next header | hop limit || |
6+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || a
| inner source IP || u
| |e t
| |n h
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+c e
| |r n
| inner destination IP |y t
| |p i
| |t c
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+e a
T| source port | dest port |d t
C+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| e
P| Sequence Number (SN) || d
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| ACK Sequence Number || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
|Off. | Rserv | Flags | Window Size || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| Checksum | Urgent Pointer || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || |
~ APPLICATION DATA ~| |
| || |
-| +-+-+-+-+-+-+-+-+| |
E| | Padding || |
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
P| Padding (continue) | Pad Length | Next Header |V V
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| Integrity Check Value-ICV (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Standard ESP VPN Packet Description
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| SPI | SN | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| IV | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--|
| Next Header | |^ |
+-+-+-+-+-+-+-+-+ || |
| || |
| inner destination IP || |
| || |a
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |u
| | source port | dest. port ~|e|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|n|h
~ (continue) | TCP Sequence Number (SN) ~|c|e
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|r|n
~ (continue) | ACK Sequence Number (SN) ~|y|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|p|i
~ (continue) |Off. | Rserv | Flags | Window Size ~|t|c
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|e|a
~ (continue) | Checksum | Urgent ~|d|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |e
~ Pointer | || |d
+-+-+-+-+-+-+-+-+ || |
~ APPLICATION DATA ~| |
| || |
| |v v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| Integrity Check Value-ICV (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Diet-ESP VPN Packet Description
The following table illustrates the activated rules and the
attributes of the Diet-ESP Context that needs an explicit agreement
to achieve the compression. All other attributes used by the rules
are part of the SA agreement. Parameters of not activated rules are
left "Unspecified".
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+--------------+-------------------+-------+
| EHC Rule | Context Attribute | Value |
+--------------+-------------------+-------+
| ESP_SPI | esp_spi_lsb | 2 |
| ESP_SN | esp_sn_lsb | 2 |
| | esp_sn_gen | |
| ESP_NH | | |
| ESP_PAD | esp_align | 8 |
| | | |
| IP6_OUTER | ip6_tcfl_comp | |
| IP6_LENGTH | | |
| IP6_HL_OUTER | ip6_hl_comp | |
| IP6_SRC | | |
+--------------+-------------------+-------+
A.3.2. IPv6 in IPv4
If the compressed inner IP header is an IPv6, but the outer IP header
is an IPv4 header, the activated rules differ, as IP6_OUTER cannot be
used. Instead, ip6_tcfl_comp and ip6_hl_comp are set to "Value".
The resulting ESP packet is the same as in Figure 8.
+--------------+-------------------+-------+
| EHC Rule | Context Attribute | Value |
+--------------+-------------------+-------+
| ESP_SPI | esp_spi_lsb | 2 |
| ESP_SN | esp_sn_lsb | 2 |
| | esp_sn_gen | |
| ESP_NH | | |
| ESP_PAD | esp_align | 8 |
| | | |
| IP6_OUTER | ip6_tcfl_comp | |
| IP6_LENGTH | | |
| IP6_HL_OUTER | ip6_hl_comp | |
| IP6_SRC | | |
+--------------+-------------------+-------+
A.3.3. IPv4 in IPv4
Figure 9 represents the original TCP packet with IPv4 inner IP
addresses and Figure 10 represents the corresponding packet
compressed with Diet-ESP. The compression with Diet-ESP results in a
reduction of 24 bytes.
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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
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
E| Security Parameters Index (SPI) | ^
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
P| Sequence Number (SN) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| IV | |
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- |
I|Version| IHL |Type of Service| Total Length |^ |
P+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
v| Identification |Flags| Fragment Offset || a
4+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| u
| Time to Live | Protocol | Header Checksum |e t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+n h
| Source Address |c e
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+r n
| Destination Address |y t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+p i
| Options | Padding |t c
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+e a
T| source port | dest port |d t
C+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| e
P| Sequence Number (SN) || d
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| ACK Sequence Number || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
|Off. | Rserv | Flags | Window Size || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| Checksum | Urgent Pointer || |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
| || |
~ APPLICATION DATA ~| |
| || |
-| +-+-+-+-+-+-+-+-+| |
E| | Padding || |
S+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |
P| Padding (continue) | Pad Length | Next Header |V V
-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| Integrity Check Value-ICV (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: Standard ESP VPN Packet Description
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| SPI | SN | ^
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| | |
| IV | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--|
|Type of Service| Protocol | inner destination IP ~^ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|| |
~ (continue) | source port || |a
|-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+| |u
| destination port | TCP Sequence Number (SN) ~|e|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|n|h
~ (continue) | ACK Sequence Number ~|c|e
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|r|n
~ (continue) |Off. | Rserv | Flags ||y|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|p|i
| Window Size | Checksum ||t|c
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+|e|a
| Urgent Pointer | APPLICATION DATA ||d|t
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +| |e
~ || |d
| || |
| |v v
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+---
| Integrity Check Value-ICV (variable) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Diet-ESP VPN Packet Description
The following table illustrates the activated rules and the
attributes of the Diet-ESP Context that needs an explicit agreement
to achieve the compression. All other attributes used by the rules
are part of the SA agreement. Parameters of not activated rules are
left "Unspecified".
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+---------------+-------------------+---------------+
| EHC Rule | Context Attribute | Value |
+---------------+-------------------+---------------+
| ESP_SPI | esp_spi_lsb | 2 |
| ESP_SN | esp_sn_lsb | 2 |
| | esp_sn_gen | "Incremental" |
| ESP_NH | | |
| ESP_PAD | esp_align | 8 |
| | | |
| IP4_OPT_DIS | | |
| IP4_LENGTH | | |
| IP4_FRAG_DIS | | |
| IP4_TTL_OUTER | | |
| IP4_CHECK | | |
| IP4_SRC | | |
+---------------+-------------------+---------------+
A.3.4. IPv4 in IPv6
If the compressed inner IP header is an IPv4, but the outer IP header
is an IPv6 header, the activated rules differ, as IP4_TTL_OUTER
cannot be used. Instead, IP4_TTL_VALUE is used. The resulting ESP
packet is the same as in Figure 10.
+--------------+-------------------+---------------+
| EHC Rule | Context Attribute | Value |
+--------------+-------------------+---------------+
| ESP_SPI | esp_spi_lsb | 2 |
| ESP_SN | esp_sn_lsb | 2 |
| | esp_sn_gen | "Incremental" |
| ESP_NH | | |
| ESP_PAD | esp_align | 8 |
| | | |
| IP4_OPT_DIS | | |
| IP4_LENGTH | | |
| IP4_FRAG_DIS | | |
| IP4_CHECK | | |
| IP4_SRC | | |
+--------------+-------------------+---------------+
Authors' Addresses
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Daniel Migault
Ericsson
8400 boulevard Decarie
Montreal, QC H4P 2N2
Canada
Email: daniel.migault@ericsson.com
Tobias Guggemos
LMU Munich
Oettingenstr. 67
80538 Munchen, Bavaria
Germany
Email: guggemos@nm.ifi.lmu.de
URI: http://www.nm.ifi.lmu.de/~guggemos
Carsten Bormann
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63921
Email: cabo@tzi.org
David Schinazi
Google LLC
1600 Amphitheatre Parkway
Mountain View, California 94043
USA
Email: dschinazi.ietf@gmail.com
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