A Bound End-to-End Tunnel (BEET) mode for ESP secunet Security Networks AGantony.antony@secunet.comsecunet Security Networks AGsteffen.klassert@secunet.com
sec
IPSECME Working GroupIKEv2BEET
This document specifies a new mode for IPsec ESP, known as Bound
End-to-End Tunnel (BEET) mode. This mode complements the existing ESP tunnel
and transport modes, while enhancing end-to-end IPsec usage. It offers the
characteristics of the tunnel mode but without its usual overhead. The BEET
mode is designed to accommodate evolving applications of ESP, such as
minimalist end-to-end tunnel, mobility and multi-address multi-homing.
Additionally, this document proposes a new Notify Message, USE_BEET_MODE, for the
Internet Key Exchange Protocol Version 2 (IKEv2) specified in
, to facilitate BEET mode Security Association
negotiation.
Introduction
The current IPsec ESP specification defines two
modes of operation: the tunnel mode and the transport mode. The tunnel mode is mainly
intended for non-end-to-end use where one or both of the ends of the
ESP Security Associations (SAs) are located in security gateways,
separate from the actual IPsec end-nodes. The transport mode is intended
for end-to-end use, where both ends of the Security Association are
terminated at the end-nodes themselves.
This document defines a new mode for ESP, called Bound End-to-End
Tunnel (BEET) mode. The purpose of the BEET mode is to provide limited
tunnel mode semantics without the overhead associated with the
regular tunnel mode. As the name states, the BEET mode is intended
solely for end-to-end use. It provides tunnel mode semantics in the
sense that the IP addresses seen by the applications and the IP
addresses used on the wire are distinct from each other, providing
the illusion that the application-level IP addresses are tunneled
over the network-level IP addresses. However, the BEET mode does not
support full tunnel semantics. More specifically, the IP addresses as seen
by the application are strictly bound. In BEET mode, only a pair of addresses
is negotiated, and only this pair of strictly bound inner addresses MUST be
used within a given BEET mode Security Association. This is in contrast to
the regular tunnel mode, where an IP address range, source range and
destination range, can be negotiated, and the inner IP addresses can be any
pair of IP addresses within the negotiated IP address range.
A BEET mode Security Association records two pairs of IP addresses,
called inner addresses and outer addresses. The inner addresses are
what the applications see. The outer addresses are what appears on
the wire. Since the inner addresses are fixed for the lifetime of
the Security Association, they need not be sent in each
packet. Instead, they are set up as the Security Associations are
created, they are verified when packets are sent, and they are
restored as packets are received.
This all gives BEET mode the efficiency of transport mode with a
limited set of end-to-end tunnel semantics. The increase efficiency is
accomplished by removing the inner IP header from the packet that is
transported on the wire. Due to this removal of the inner IP header, the TTL
of a tunneled packet is reduced at every router on the path as the TTL
value is copied from inner to outer header by the sender and vice
versa by the receiver. The semantics of BEET mode is limited in the
sense that only one fixed pair of inner addresses is allowed. The
outer addresses may change over the lifetime of the SA, but the
inner addresses cannot. If a new pair of inner addresses is needed,
a new BEET mode Security Association must be established.
In the cases considered here, a single pair of security associations between any
single pair of nodes is usually sufficient.
Requirements LanguageThe key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in
RFC 2119.Terminology
In this section we define terms specific to this document. This section
is normative.
Inner IP address :
An IP address as seen by applications, typically stored in TCP or other
upper layer data structures. It is processed by the IP stack prior
to ESP processing in the output side and after ESP processing in
the input side.
Outer IP address: An IP address seen on the wire and processed by the IP
stack after ESP processing in the output side and before ESP processing
in the input side.
Inner IP header: An IP header that contains inner IP addresses. In some cases an
inner IP header may be represented as an internal data structure
containing data equivalent to an IP header.
Outer IP header: An IP header that contains outer IP addresses. In some cases an
outer IP header may be represented as an internal data structure
containing the data equivalent to an IP header.
Background
For years, the idea of a minimal IPsec tunnel mode for end-to-end security has
sparked discussions and innovation. BEET mode has been in use for over a decade.
It hs the potential to improve secure data transmission. Once BEET mode is
standardized its potential for enhancing secure communications would increase
with interoperablity. Related work
The basic idea captured by this draft has been floating around for a
long time. Steven Bellovin's HostNAT talk [8] and at the Los Angeles IETF
is an early example, and this ID is based on BEET mode ID
. The same idea has surfaced
several times. Perhaps the most concrete current proposal is the Host
Identity Protocol (HIP) and
where BEET-mode ESP processing is an integral part of the overall protocol
without IKE negotiation. The updated version of the Host Identity Protocol
(HIPv2) and recommend the
use of BEET mode.
Minimal ESP can also benefit from the use BEET mode.
It reduces the outter packet size by 20 - 40 bytes per packet, by ommiting
inner IPv4/IPv6 header, compared to tunnel mode.
However did not recommend the use of BEET mode, as
it is not yet standardized
Use scenarios
In this section we describe a number of possible use scenarios. None of
these scenarios are meant to be complete specifications on how exactly
to support the functionality. Separate specifications are needed for
that. Instead, the purpose of this section is to discuss the overall
benefits of BEET mode, and to lay out a road map for possible future
documents. This section is informative.
Minimal IPsec for end-to-end
Over the years, BEET-mode has been widely adopted as a minimal IPsec tunnel
for end-to-end scenarios, effectively reducing data transmission over
the wire. It also helps alleviate MTU issues.
Additionally, BEET is valuable for low-power devices, as it reduces
power consumption and complexity. In situations where devices
or IPsec connections are dedicated to a single application or transport protocol,
BEET mode simplifies packet processing and conserves energy, especially for
lower-powered devices.
NAT traversal
NAT traversal is currently a major issue in IPsec. Encapsulating packets into
UDP using
Transport mode may suffice in some cases, but it becomes inadequate when
multiple clients are behind a NAT gateway. In such situations, tunnel mode
becomes necessary.
BEET mode offers tunnel mode semantics without the additional packet overhead
associated with traditional tunnel mode when operating behind a NAT gateway.
A pair of BEET-mode Security Associations (SAs) can effectively "un-NAT"
packets originationg from behind a NAT gatewa as they traverse the network.
[AA do we need this ?? This process is illustrated in Figure 1.]
[SK: The figure and the comments from the old draft is missing here.
Is the scenario where a client behind NAT knows it's public address
common? Maybe ask Pablo.]End-node multi-address multi-homing
BEET mode enables limited end-node multi-address multi-homing. It
establishes a tunnel between end-hosts with fixed inner IP addresses,
allowing multi-homed hosts to use different outer IP addresses in
various packets without impacting upper-layer protocols.
Upper-layer protocols consistently see the inner IP address, ensuring
seamless communication over fixed IP addresses.
Implementing this kind of limited multi-homing support would require
a small change to the current IPsec SPD and SA implementations.
Currently the incoming SA selection is based on the SPI and
destination address, with the implicit assumption that there is only
one possible destination address for each incoming SA. In a multi-
homed host it would be desirable to have multiple destination
addresses associated with the SA, thereby allowing the same SA to be
used independent on the actual destination address in the packets.
Removing the destination address from unicast SA lookup is already
being proposed in the current ESP . [AA verify this part]
Protocol Definition
In this section we define the exact protocol formats and operations. This section is normative.
Changes to Security Association data structure
A BEET mode Security Association contains the same data as a regular
tunnel mode Security Association, with the exception that the inner
selectors must be single addresses and cannot be subnets. The data
includes the following:
A pair of inner IP addresses.
A pair of outer IP addresses.
Cryptographic keys and other data as defined in Section 4.4.2.
A conforming implementation MAY store the data in a way similar to a
regular tunnel mode Security Association.
Note that in a conforming implementation, the inner and outer
addresses MAY belong to different address families. All
implementations that support both IPv4 and IPv6 SHOULD support both
IPv4-over-IPv6 and IPv6-over-IPv4 tunneling.
Packet format
The wire packet format is identical to the ESP transport mode wire
format as defined in Section 3.1.1. However,
the resulting packet contains outer IP addresses instead of the inner IP addresses
received from the upper layer. The construction of the outer headers
is defined in Section 5.1.2. The following diagrams
illustrates ESP BEET mode positioning for typical IPv4 and IPv6
packets. [SK: The figures are not consistent. Let's discuss this in a call.
Why is dest opts. in IPv6 encrypted, but other ext hdrs are not?Inner IPv4 DatagramIPv4 INNER DATAGRAM BEFORE APPLYING ESP AFTER APPLYING ESP, OUTER v4 ADDRESSES |
|<-------- integrity ------->|
]]>AFTER APPLYING ESP, OUTER v6 ADDRESSES|
|<------ integrity -------->|
]]>IPv4 INNER DATAGRAM with IP options BEFORE APPLYING ESPIPv4 AFTER APPLYING ESP, OUTER v4 ADDRESSES INNER IPv4 OPTIONS |
|<----------- integrity -------------->|
PH = BEET mode Pseudo-Header
]]>IPv4 + OPTIONS AFTER APPLYING ESP, OUTER IPv6 ADDRESSES |
|<---------- integrity --------------->|
PH = BEET mode Pseudo-Header
]]>Inner IPv6 Datagram IPv6 DATAGRAM BEFORE APPLYING ESP IPv6 DATAGRAM AFTER APPLYING ESP, OUTER IPv6 ADDRESSES |
|<-------------- integrity -------------->|
]]> IPv6 DATAGRAM AFTER APPLYING ESP, OUTER IPv4 ADDRESSES |
|<----------- integrity ----------->|
]]>Cryptographic processing
The outgoing packets MUST be protected exactly as in ESP transport
mode . That is, the upper layer protocol packet is wrapped into
an ESP header, encrypted, and authenticated exactly as if regular
transport mode was used. The resulting ESP packet is subject to IP
header processing as defined in and
. The incoming ESP protected messages
are verified and decrypted exactly as if regular transport mode was used.
The resulting cleartext packet is subject to IP header processing as
defined in and IP header processing
The biggest difference between BEET mode and the other two modes
lies in the way IP headers are processed. In regular transport mode, the IP
header is kept intact. In the regular tunnel mode, an outer IP header
is created on output and discarded on input. In BEET mode, the IP
header is replaced with another one on both input and output.
On the BEET mode output side, the IP processing MUST first ensure that
the IP addresses in the original IP header contain the inner addresses
as specified in the SA. This MAY be ensured by proper policy processing,
and it is possible that no checks are needed at the SA processing time.
Once the IP header has been verified to contain the right IP inner
addresses, it is discarded. A new IP header is derived, using the
discarded inner header as a hint for other fields except the IP
addresses, the IPv4 options, the IPv6 optional extensions,
and the IPv4 fragmentation offset when the packet is a fragment.
The IP addresses in the new header MUST be the outer tunnel addresses.
On the input side, the received IP header is simply discarded. Since the
packet has been decrypted and verified, no further checks are necessary.
A new IP header, corresponding to a tunnel mode inner header, is derived,
using the discarded outer header as a hint for other fields but the IP
addresses, the IPv4 options, the IPv6 optional extensions, and the IPv4
fragmentation offset when the packet is a fragment. The IP addresses in
the new header MUST be the inner addresses negotiated.
As the outer header fields are used as a hint for creating the inner
header, it must be noted that the BEET inner header differs from
tunnel mode inner headers. In BEET mode, an inner header will contain
the TTL, DF-bit and other option values from the outer header. The
TTL, DF-bit and other option values of the inner header MUST be
processed by the stack. [AA would we loose the DF value?? if IPsec gateway has different policy?
or is possible to restore the same as inner packet?]
Handling of outgoing packets
The outgoing BEET mode packets are processed as follows:
The system MUST verify that the IP header contains the inner
source and destination addresses, exactly as defined in the SA.
This verification MAY be explicit, or it MAY be implicit, for
example, as a result of prior policy processing. Note that in
some implementations there may be no real IP header at this time,
but the source and destination addresses may be carried out-of-
band. In case the source address is still unassigned, it SHOULD
be ensured that the designated inner source address would be
selected at a later stage.
The IP payload (the contents of the packet beyond the IP header)
is wrapped into an ESP header as defined in Section 3.3.
A new IP header is constructed, replacing the original one. The
new IP header MUST contain the outer source and destination
addresses, as defined in the SA. Note that in some
implementations there may be no real IP header at this time but
the source and destination addresses may be carried out-of-band.
In cases where the source address must be left unassigned, it
SHOULD be ensured that the right source address is selected at
a later stage. Other than the addresses, it is RECOMMENDED that
the new IP header copies the fields from the original IP header,
unless the packet is a IP fragment.
If there are any IPv4 options in the original packet, they are copied into
ESP payload. The IPv4 options are tunneled between the tunnel end-points.
The sender MUST encapsulate the options as defined in
.
If the packet is an IPv4 fragment, the flags and the fragment
offset field from the inner IP packet MUST NOT be copied.
Instead these two fields MUST be encapsulated with a PH
header as defined in .
Instead of literally discarding the IP header and constructing a new one,
a conforming implementation MAY simply replace the addresses in an
existing header. However, if the RECOMMENDED feature of allowing the inner
and outer addresses from different address families is used, this simple
strategy does not work.
Handling of incoming packets
The incoming BEET mode packets are processed as follows:
The system MUST successfully verify and decrypt the incoming packet, as
specified in section 3.4. If the verification
or decryption fails, the packet MUST be discarded.
The original IP header is discarded without further verification since
the ESP verification has already confirmed the packet's integrity and source.
The packet can be safely assumed to have arrived from the right sender.
A new IP header is constructed, replacing the original one. The
new IP header MUST contain the inner source and destination
addresses, as defined in the SA. If the sender has set the ESP
next protocol field to 94 and included the Pseudo-Header as
described in , the receiver MUST include the options
after the constructed IP header. Note, that in some
implementations the real IP header may have already been
discarded and the source and destination addresses are carried
out-of-band. In such case the out-of-band addresses MUST be the
inner addresses. Other than the addresses, it is RECOMMENDED
that the new IP header copies the fields from the original IP
header. [AA how about ESP in UDP and mapping changes?]
Alternatively, a conforming implementation MAY replace the addresses in an
existing header rather than discarding it and creating a new one.
However, if the RECOMMENDED feature of allowing
the inner and outer addresses from different address families is
used, this simple strategy does not work.
IPv4 Pseudo Header
In BEET mode, if IPv4 options or IPv6 optional extensions are transported
inside the tunnel, as ESP payload. For IPv4, the sender MUST include a
Pseudo Header(PH) after ESP header.
The pseudo-headerr indicates the IPv4 packet has options or the fragmentation
flags and fragmentation offset is set.
The sender MUST set the next protocol field on the ESP header as 94.
The resulting pseudo header including the IPv4 options, MUST be padded
to 8 octet boundary. The padding length is expressed in octets,
valid padding lengths are 0 or 4 octets as the original IPv4 options
are already padded to 4 octet boundary. The padding MUST be filled
with NOP options as defined in Internet Protocol
section 3.1 Internet header format. The padding is added in front of the
original options to ensure that the receiver is able to reconstruct
the original IPv4 datagram. The Header Length field contains the
length of the IPv4 options, and padding in 8 octets units.
BEET mode pseudo header format
Next Header - Identifies the data following this header.
Header Len - 8-bit unsigned integer. Length of the pseudo header in
8-octet units, including IHF and Fragment offset, IPv4 options, when present, not including the first 8 octets.
Pad Len - 8-bits unsigned integer. Length of padding in octets, valid padding lengths are:
0, 4 : no IPv4 fragment and options are present [AA Note : old case]
2, 6 : IPv4 fragment and no IPv4 options.
2, 6 : IPv4 fragment and options.
F - 2 bits Flags. 00 IP options, 01 Fragment, 10 IP options and Fragment, 11 Reserved
Reserved - Lower 6-bits, set to zero
IHF - Flags from the inner IP header (optional) when F = 01 or 10
Fragment offset 13 bits - Fragment offset from the inner IP header (optional) when F = 01 or 10
Padding - 0, 2 or 4 octets of zeros, depending on the fragment flag.
IPv4 options - IPv4 options from the inner IP header with optional padding. Alligned to 32 bits.
The receiver MUST remove this pseudo-header and padding as a part of BEET
processing, in order to reconstruct the original IPv4 datagram. The IPv4
options included in the pseudo-header MUST be added after the reconstructed
IPv4 (inner) header on the receiving side. Also copy the flags and Fragment offset
when the PH flags is 01, 10.
Note: when the IPv4 options are present, the outer header's IHL would be
different from the inner header IHL.
The receiver MUST remove this pseudo-header and padding as a part of
BEET processing, in order reconstruct the original IPv4 datagram.
The IPv4 options included into the pseudo-header MUST be added after
the reconstructed IPv4 (inner) header on the receiving side.
Note: When the pseudo-header is present due to the presence of IPv4 options
in the inner IP header, the outer header's IHL (Internet Header Length) would
be different from the inner IP header IHL.
IPv4 Inner Fragments
When the inner IPv4 datagram is a fragment (as specified by the
"more-fragments" flag being set to one ), this flag
MUST NOT be copied to the outer ESP datagram header. Additionally, for any
non-first fragment with a "more-fragments" flag or "fragment offset field,"
these two fields MUST NOT be copied to the outer IPv4 header of the ESP
datagram.
Here are a few possible ways to deal with these IPv4 fragments.
Re-assemble the IPv4 fragments, send to ESP, and ESP datagram may be
fragmented as required.
Drop the IPv4 fragments, i.e., BEET mode IPv4 support for fragments is
optional.
Copy the fragment flag and offset length from the inner IPv4 header to
BEET pseudo-header .
Explore other solutions? [TBD?]
TBD Discuss/Decide which of the above options make sense. IPv6 inner Fragments
It's crucial to highlight that IPv6 uses fragmentation information in a
distinct manner than IPv4 Section 4.5.
Specifically, an IPv6 fragment uses IPv6 optional extensions for
fragments. BEET mode treats the IPv6 optional extensions as ESP payload and move from inner header to ESP payload.
Mixed family IPv4 inside and IPv6 outside
The inner datagram's IP version MUST be independent of the outer IP
version. The inner address family and address are taken from the
negotiated Traffic Selectors. When the inner datagram contains IPv4
with fragments or IPv4 options, use .
Mixed family IPv6 inside and IPv4 outside
When the inner datagram is an IPv6 datagram with IPv6 optional
extensions, copy it into ESP payload .
Policy Considerations
In this section we describe how BEET mode affects on IPsec policy
processing. This section is normative.
A BEET Security Association SHOULD NOT be used with NULL
authentication.
On the output side, the IPsec policy processing mechanism SHOULD take
care that only packets with IP addresses matching the inner
addresses of a Security Association are passed on to that Security
Association. If the policy mechanism does not provide full assurance
on this point, the SA processing MUST check the addresses. Further policy
distinction may be specified based on IP version, upper layer
protocol, and ports. If such restrictions are defined, they MUST be
enforced.
On the output side, the policy rules SHOULD prevent any packets
containing the pair of inner IP addresses from escaping to the wire in
cleartext.
On the input side,no policy processing is necessary for
encrypted packets. The SA is deduced from the SPI and destination
address. A single SA MAY be associated with several outter destination
addresses. Since the outer IPsec addresses are discarded, and since
the packet authenticity and integrity are protected by ESP, there is
no need to check the outer addresses. Since the inner addresses are
fixed and restored from the SA, there is no need to check them.
There MAY be further policy rules specifying allowed upper layer
protocols and ports. If such restrictions are defined, they MUST be
enforced.
On the input side, there SHOULD be a policy rule that filters out
cleartext packets that contain the inner addresses.
Security Considerations In this section we discuss the security properties of the BEET mode,
discussing some and point out some of its limitations .
There are no known new vulnerabilities that the introduction of the
BEET mode would create.
It is currently possible to implement the equivalent of BEET mode by
using transport mode ESP and explicit network address translation at
the end-hosts themselves. However, such an implementation is more
complex, less flexible, and potentially more vulnerable to security
problems that are caused by misconfigurations; see Section 9.
The main security benefit is an operational one. To implement the
same functionality without BEET mode typically requires
configuring three different, unrelated components in the hosts.
The transport mode ESP SAs must be configured.
A host-based NAT function must be configured to properly translate
between the inner and outer addresses.
A host firewall must be configured to properly filter out packets
so that inner addresses do not leak in or out.
While it may be possible to configure these components to achieve the
same functionality, such a configuration is error prone, increasing
the probability of security vulnerabilities. An integrated BEET mode
implementation is less prone to configuration mistakes. Furthermore,
it would be fairly hard to implement portable key management
protocols that would be able to configure all of the required
components at the same time. On the other hand, it would be easy to
provide a portable key management protocol implementation that would
be able to configure BEET mode SAs through the specified PF_KEY
extensions.
Since the BEET security associations have the semantics of a fixed,
point-to-point tunnel between two IP addresses, it is possible to
place one or both of the tunnel end0points into other nodes but those
that actually "possess" the inner IP addresses, i.e., to implement a
BEET mode proxy. However, since such usage defeats the security
benefits of combined ESP and hostNAT processing, as discussed above,
the implementations SHOULD NOT support such usage.
Because in BEET mode the outer header source address is not checked at
the time of input handling, there is a potential for a DoS attack
where the attacker would send random packets that match the SPI of
some BEET-mode SA. This kind of attack would cause the victim to
perform unnecessary integrity checks that would result in a failure.
However, if this kind of behavior is detected, the node may request rekeying
using IKEv2 rekey, and after rekeying. If the attacker
was not on the path, the new SPI value would not be known by the
attacker.
IKEv2 Negotiation
When negotiating a Child SA using using IKEv2, the initiator may use
the new "USE_BEET_MODE" Notify Message to request a Child SA pair with
BEET mode support. The method used is similar to how USE_TRANSPORT_MODE
is negotiated, as described in
To request a BEET-mode SA on the Child SA pair, the initiator MUST
include the USE_BEET_MODE Notify Message when requesting a new Child
SA, either during the IKE_AUTH or CREATE_CHILD_SA exchanges.
If the request is accepted, the response MUST also include a USE_BEET_MODE
notification. If the responder declines and does not include the
USE_BEET_MODE notification in the response, the child SA will be
established without BEET mode enabled. If this is unacceptable to the
initiator, the initiator MUST delete the child SA.
Payload Length - MUST be 0.
Protocol ID (1 octet) - MUST be 0. MUST be ignored if not 0.
SPI Size (1 octet) - MUST be 0. MUST be ignored if not 0.
This document defines a new IKEv2 Notify Message Type payloads for the IANA "IKEv2 Notify Message Types - Status Types" registry.
Implementation Status
[Note to RFC Editor: Please remove this section and the reference to
before publication.]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of
this Internet-Draft, and is based on a proposal described in
. The description of implementations in this
section is intended to assist the IETF in its decision processes
in progressing drafts to RFCs. Please note that the listing of
any individual implementation here does not imply endorsement
by the IETF. Furthermore, no effort has been spent to verify the
information presented here that was supplied by IETF contributors.
This is not intended as, and must not be construed to be, a catalog
of available implementations or their features. Readers are advised
to note that other implementations may exist.
According to , "this will allow reviewers
and working groups to assign due consideration to documents that
have the benefit of running code, which may serve as evidence of
valuable experimentation and feedback that have made the implemented
protocols more mature. It is up to the individual working groups
to use this information as they see fit".
Authors are requested to add a note to the RFC Editor at the
top of this section, advising the Editor to remove the entire
section before publication, as well as the reference to .
Linux
Organization:
Linux kernel Project
Name:
Linux Kernel https://www.kernel.org/
Description:
Implements BEET mode in ESP. The initial support was added in 2006. It is widely used
Level of maturity:
Stable used for over 15 years
Licensing:
GPLv2
Implementation experience:
There is no support for IPv4 fragments yet. IPv6 fragments
appears to work. The BEE mode code is in production for over a decade
Implements BEET mode support in ESP. e.g. command support "ip xfrm policy ... mode beet" . and "ip xfrm state .. mode beet". The initial support was added in 2006
Level of maturity:
Stable
Licensing:
GPLv2
Implementation experience:
TBD
Contact:
https://lore.kernel.org/netdev/ or Stephen Hemminger stephen@networkplumber.org
Acknowledgments
We sincerely thank the previous authors and contributors whose work laid the
foundation for this document. Their insights and dedication have greatly
influenced our work, also their contributions to the BEET mode
implementation many years ago.
Special thanks to Peka Nikander for generously granting permission to use
their previous work .
We appreciate the guidance and support from Tero Kivinen in reaching out to
previous authors during the document's development.
Our gratitude also goes to all those who provided feedback, guidance, and
support throughout this document's development and operational experience.
Your contributions were vital in making this work possible.
Normative ReferencesInformative ReferencesAdditional StuffThis becomes an Appendix.