rfc9853.original   rfc9853.txt 
TLS H. Tschofenig, Ed. Internet Engineering Task Force (IETF) H. Tschofenig, Ed.
Internet-Draft H-BRS Request for Comments: 9853 H-BRS
Updates: 9146, 9147 (if approved) A. Kraus Updates: 9146, 9147 A. Kraus
Intended status: Standards Track Category: Standards Track
Expires: 15 January 2026 T. Fossati ISSN: 2070-1721 T. Fossati
Linaro Linaro
14 July 2025 February 2026
Return Routability Check for DTLS 1.2 and DTLS 1.3 Return Routability Check for DTLS 1.2 and 1.3
draft-ietf-tls-dtls-rrc-20
Abstract Abstract
This document specifies a return routability check for use in context This document specifies a Return Routability Check (RRC) for use in
of the Connection ID (CID) construct for the Datagram Transport Layer the context of the Connection ID (CID) construct for the Datagram
Security (DTLS) protocol versions 1.2 and 1.3. Transport Layer Security (DTLS) protocol versions 1.2 and 1.3.
Implementations offering the CID functionality described in RFC 9146
and RFC 9147 are encouraged to also provide the return routability
check functionality described in this document. For this reason,
this document updates RFC 9146 and RFC 9147.
Discussion Venues
This note is to be removed before publishing as an RFC.
Discussion of this document takes place on the Transport Layer
Security Working Group mailing list (tls@ietf.org), which is archived
at https://mailarchive.ietf.org/arch/browse/tls/.
Source for this draft and an issue tracker can be found at Implementations offering the CID functionality described in RFCs 9146
https://github.com/tlswg/dtls-rrc. and 9147 are encouraged to also provide the RRC functionality
described in this document. For this reason, this document updates
RFCs 9146 and 9147.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This document is a product of the Internet Engineering Task Force
Task Force (IETF). Note that other groups may also distribute (IETF). It represents the consensus of the IETF community. It has
working documents as Internet-Drafts. The list of current Internet- received public review and has been approved for publication by the
Drafts is at https://datatracker.ietf.org/drafts/current/. Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Internet-Drafts are draft documents valid for a maximum of six months Information about the current status of this document, any errata,
and may be updated, replaced, or obsoleted by other documents at any and how to provide feedback on it may be obtained at
time. It is inappropriate to use Internet-Drafts as reference https://www.rfc-editor.org/info/rfc9853.
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 15 January 2026.
Copyright Notice Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 3 2. Conventions and Terminology
3. RRC Extension . . . . . . . . . . . . . . . . . . . . . . . . 4 3. RRC Extension
3.1. RRC and CID Interplay . . . . . . . . . . . . . . . . . . 4 3.1. RRC and CID Interplay
4. Return Routability Check Message Types . . . . . . . . . . . 5 4. Return Routability Check Message Types
5. Path Validation Procedure . . . . . . . . . . . . . . . . . . 6 5. Path Validation Procedure
5.1. Basic . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5.1. Basic
5.2. Enhanced . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Enhanced
5.3. Path Challenge Requirements . . . . . . . . . . . . . . 8 5.3. Path Challenge Requirements
5.4. Path Response/Drop Requirements . . . . . . . . . . . . . 9 5.4. Path Response/Drop Requirements
5.5. Timer Choice . . . . . . . . . . . . . . . . . . . . . . 9 5.5. Timer Choice
6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 6. Example
7. Operational Considerations . . . . . . . . . . . . . . . . . 11 7. Operational Considerations
7.1. Logging Anomalous Events . . . . . . . . . . . . . . . . 12 7.1. Logging Anomalous Events
7.2. Middlebox Interference . . . . . . . . . . . . . . . . . 12 7.2. Middlebox Interference
8. Security Considerations . . . . . . . . . . . . . . . . . . . 12 8. Security Considerations
8.1. Attacker Model . . . . . . . . . . . . . . . . . . . . . 13 8.1. Attacker Model
8.1.1. Amplification . . . . . . . . . . . . . . . . . . . . 14 8.1.1. Amplification
8.1.2. Off-Path Packet Forwarding . . . . . . . . . . . . . 14 8.1.2. Off-Path Packet Forwarding
9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18 9. Privacy Considerations
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 10. IANA Considerations
10.1. New TLS ContentType . . . . . . . . . . . . . . . . . . 19 10.1. New TLS ContentType
10.2. New TLS ExtensionType . . . . . . . . . . . . . . . . . 19 10.2. New TLS ExtensionType
10.3. New "TLS RRC Message Type" Registry . . . . . . . . . . 20 10.3. New "TLS RRC Message Type" Registry
10.3.1. Designated Expert Instructions . . . . . . . . . . . 21 10.3.1. Designated Expert Instructions
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 21 11. References
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 21 11.1. Normative References
12.1. Normative References . . . . . . . . . . . . . . . . . . 22 11.2. Informative References
12.2. Informative References . . . . . . . . . . . . . . . . . 23 Acknowledgments
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 23 Authors' Addresses
1. Introduction 1. Introduction
A Connection ID (CID) is an identifier carried in the record layer A Connection ID (CID) is an identifier carried in the record layer
header of a DTLS datagram that gives the receiver additional header of a DTLS datagram that gives the receiver additional
information for selecting the appropriate security context. The CID information for selecting the appropriate security context. The CID
mechanism has been specified in [RFC9146] for DTLS 1.2 and in mechanism has been specified in [RFC9146] for DTLS 1.2 and in
[RFC9147] for DTLS 1.3. [RFC9147] for DTLS 1.3.
Section 6 of [RFC9146] describes how the use of CID increases the Section 6 of [RFC9146] describes how the use of CID increases the
attack surface of DTLS 1.2 and 1.3 by providing both on-path and off- attack surface of DTLS 1.2 and 1.3 by providing both on-path and off-
path attackers an opportunity for (D)DoS. It also describes the path attackers an opportunity for DoS or DDoS. It also describes the
steps a DTLS principal must take when a record with a CID is received steps a DTLS principal must take when a record with a CID is received
that has a source address different from the one currently associated that has a source address different from the one currently associated
with the DTLS connection. However, the actual mechanism for ensuring with the DTLS connection. However, the actual mechanism for ensuring
that the new peer address is willing to receive and process DTLS that the new peer address is willing to receive and process DTLS
records is left open. To address the gap, this document defines a records is left open. To address the gap, this document defines a
Return Routability Check (RRC) sub-protocol for DTLS 1.2 and 1.3 Return Routability Check (RRC) subprotocol for DTLS 1.2 and 1.3,
inspired by the path validation procedure defined in Section 8.2 of inspired by the path validation procedure defined in Section 8.2 of
[RFC9000]. As such, this document updates [RFC9146] and [RFC9147]. [RFC9000]. As such, this document updates [RFC9146] and [RFC9147].
The return routability check is performed by the receiving endpoint The return routability check is performed by the receiving endpoint
before the CID-address binding is updated in that endpoint's session before the CID-address binding is updated in that endpoint's session
state. This is done in order to give the receiving endpoint state. This is done in order to give the receiving endpoint
confidence that the sending peer is in fact reachable at the source confidence that the sending peer is in fact reachable at the source
address indicated in the received datagram. For an illustration of address indicated in the received datagram. For an illustration of
the handshake and address validation phases, see Section 6. the handshake and address validation phases, see Section 6.
Section 5.1 of this document explains the fundamental mechanism that Section 5.1 of this document explains the fundamental mechanism that
aims to reduce the DDoS attack surface. Additionally, in aims to reduce the DDoS attack surface. Additionally, Section 5.2
Section 5.2, a more advanced address validation mechanism is discusses a more advanced address validation mechanism. This
discussed. This mechanism is designed to counteract off-path mechanism is designed to counteract off-path attackers trying to
attackers trying to place themselves on-path by racing packets that place themselves on-path by racing packets that trigger address
trigger address rebinding at the receiver. To gain a detailed rebinding at the receiver. To gain a detailed understanding of the
understanding of the attacker model, please refer to Section 8.1. attacker model, please refer to Section 8.1.
Apart from of its use in the context of CID-address binding updates, Apart from of its use in the context of CID-address binding updates,
the path validation capability offered by RRC can be used at any time the path validation capability offered by RRC can be used at any time
by either endpoint. For instance, an endpoint might use RRC to check by either endpoint. For instance, an endpoint might use RRC to check
that a peer is still reachable at its last known address after a that a peer is still reachable at its last known address after a
period of quiescence. period of quiescence.
2. Conventions and Terminology 2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
skipping to change at page 4, line 18 skipping to change at line 147
of [RFC8446]. of [RFC8446].
In this document, the term "anti-amplification limit" means three In this document, the term "anti-amplification limit" means three
times the amount of data received from an unvalidated address. This times the amount of data received from an unvalidated address. This
includes all DTLS records originating from that source address, includes all DTLS records originating from that source address,
excluding those that have been discarded. This follows the pattern excluding those that have been discarded. This follows the pattern
of [RFC9000], applying a similar concept to DTLS. of [RFC9000], applying a similar concept to DTLS.
The term "address" is defined in Section 1.2 of [RFC9000]. The term "address" is defined in Section 1.2 of [RFC9000].
The terms "client", "server", "peer" and "endpoint" are defined in The terms "client", "server", "peer", and "endpoint" are defined in
Section 1.1 of [RFC8446]. Section 1.1 of [RFC8446].
3. RRC Extension 3. RRC Extension
The use of RRC is negotiated via the rrc extension. The rrc The use of RRC is negotiated via the rrc extension. The rrc
extension is only defined for DTLS 1.2 and DTLS 1.3. On connecting, extension is only defined for DTLS 1.2 and 1.3. On connecting, a
a client wishing to use RRC includes the rrc extension in its client wishing to use RRC includes the rrc extension in its
ClientHello. If the server is capable of meeting this requirement, ClientHello. If the server is capable of meeting this requirement,
it responds with a rrc extension in its ServerHello. The it responds with an rrc extension in its ServerHello. The
extension_type value for this extension is TBD1 and the extension_type value for this extension is 61, and the extension_data
extension_data field of this extension is empty. A client offering field of this extension is empty. A client offering the rrc
the rrc extension MUST also offer the connection_id extension extension MUST also offer the connection_id extension [RFC9146]. If
[RFC9146]. If the client includes the rrc extension in its the client includes the rrc extension in its ClientHello but omits
ClientHello but omits the connection_id extension, the server MUST the connection_id extension, the server MUST NOT include the rrc
NOT include the rrc extension in its ServerHello. A client offering extension in its ServerHello. A client offering the connection_id
the connection_id extension SHOULD also offer the rrc extension, extension SHOULD also offer the rrc extension, unless the application
unless the application using DTLS has its own address validation using DTLS has its own address validation mechanism. The client and
mechanism. The client and server MUST NOT use RRC unless both sides server MUST NOT use RRC unless both sides have successfully exchanged
have successfully exchanged rrc extensions. rrc extensions.
3.1. RRC and CID Interplay 3.1. RRC and CID Interplay
RRC offers an in-protocol mechanism to perform peer address RRC offers an in-protocol mechanism to perform peer address
validation that complements the "peer address update" procedure validation that complements the "peer address update" procedure
described in Section 6 of [RFC9146]. Specifically, when both CID described in Section 6 of [RFC9146]. Specifically, when both CID
[RFC9146] and RRC have been successfully negotiated for the session, [RFC9146] and RRC have been successfully negotiated for the session,
if a record with CID is received that has the source address of the if a record with CID is received that has the source address of the
enclosing UDP datagram different from what is currently associated enclosing UDP datagram different from what is currently associated
with that CID value, the receiver SHOULD perform a return routability with that CID value, the receiver SHOULD perform a return routability
check as described in Section 5, unless an application-specific check as described in Section 5, unless an application-specific
address validation mechanism can be triggered instead (e.g., CoAP address validation mechanism can be triggered instead (e.g.,
Echo [RFC9175]). Constrained Application Protocol (CoAP) Echo [RFC9175]).
4. Return Routability Check Message Types 4. Return Routability Check Message Types
This document defines the return_routability_check content type This document defines the return_routability_check content type
(Figure 1) to carry Return Routability Check messages. (Figure 1) to carry Return Routability Check messages.
The RRC sub-protocol consists of three message types: path_challenge, The RRC subprotocol consists of three message types: path_challenge,
path_response and path_drop that are used for path validation and path_response, and path_drop. These message types are used for path
selection as described in Section 5. validation and selection as described in Section 5.
Each message carries a Cookie, an 8-byte field containing 64 bits of Each message carries a Cookie, an 8-byte field containing 64 bits of
entropy (e.g., obtained from the CSPRNG used by the TLS entropy (e.g., obtained from the cryptographically secure
implementation, see Appendix C.1 of [RFC8446]). pseudorandom number generator (CSPRNG) used by the TLS
implementation; see Appendix C.1 of [RFC8446]).
The return_routability_check message MUST be authenticated and The return_routability_check message MUST be authenticated and
encrypted using the currently active security context. encrypted using the currently active security context.
enum { enum {
invalid(0), invalid(0),
change_cipher_spec(20), change_cipher_spec(20),
alert(21), alert(21),
handshake(22), handshake(22),
application_data(23), application_data(23),
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rrc_msg_type msg_type; rrc_msg_type msg_type;
select (return_routability_check.msg_type) { select (return_routability_check.msg_type) {
case path_challenge: Cookie; case path_challenge: Cookie;
case path_response: Cookie; case path_response: Cookie;
case path_drop: Cookie; case path_drop: Cookie;
}; };
} return_routability_check; } return_routability_check;
Figure 1: Return Routability Check Message and Content Type Figure 1: Return Routability Check Message and Content Type
Future extensions to the RRC sub-protocol may define new message Future extensions to the RRC subprotocol may define new message
types. Implementations MUST be able to parse and understand the types. Implementations MUST be able to parse and understand the
three RRC message types defined in this document. In addition, three RRC message types defined in this document. In addition,
implementations MUST be able to parse and gracefully ignore messages implementations MUST be able to parse and gracefully ignore messages
with an unknown msg_type. with an unknown msg_type.
5. Path Validation Procedure 5. Path Validation Procedure
A receiver that observes the peer's address change MUST stop sending A receiver that observes the peer's address change MUST stop sending
any buffered application data, or limit the data sent to the any buffered application data or limit the data sent to the
unvalidated address to the anti-amplification limit. It then unvalidated address to the anti-amplification limit. It then
initiates the return routability check. initiates the return routability check.
This document describes two kinds of checks: basic (Section 5.1) and This document describes two kinds of checks: basic (Section 5.1) and
enhanced (Section 5.2). The choice of one or the other depends on enhanced (Section 5.2). The choice of one or the other depends on
whether the off-path attacker scenario described in Section 8.1.2 is whether the off-path attacker scenario described in Section 8.1.2 is
to be considered. (The decision on what strategy to choose depends to be considered. (The decision on what strategy to choose depends
mainly on the threat model, but may also be influenced by other mainly on the threat model but may also be influenced by other
considerations. Examples of impacting factors include: the need to considerations. Examples of impacting factors include the need to
minimise implementation complexity, privacy concerns, and the need to minimise implementation complexity, privacy concerns, and the need to
reduce the time it takes to switch path. The choice may be offered reduce the time it takes to switch path. The choice may be offered
as a configuration option to the user of the TLS implementation.) as a configuration option to the user of the TLS implementation.)
After the path validation procedure is completed, any pending send After the path validation procedure is complete, any pending send
operation is resumed to the bound peer address. operation is resumed to the bound peer address.
Section 5.3 and Section 5.4 list the requirements for the initiator Sections 5.3 and 5.4 list the requirements for the initiator and
and responder roles, broken down per protocol phase. responder roles, broken down per protocol phase.
Please note that the presented algorithms are not designed to handle Please note that the presented algorithms are not designed to handle
nested rebindings, i.e. rebindings that may occur while a path is nested rebindings, i.e. rebindings that may occur while a path is
being validated following a previous rebinding. If this happens being validated following a previous rebinding. This should rarely
(which should rarely occur), the path_response message is dropped, occur, but if it happens, the path_response message is dropped, the
the address validation times out, and the address will not be address validation times out, and the address will not be updated. A
updated. A new path validation will start when new data is received. new path validation will start when new data is received.
Also note that in the event of a NAT rebind, the initiator and Also, note that in the event of a NAT rebind, the initiator and
responder will have different views of the path: the initiator will responder will have different views of the path: The initiator will
see a new path, while the responder will still see the old one. see a new path, while the responder will still see the old one.
5.1. Basic 5.1. Basic
The basic return routability check comprises the following steps: The basic return routability check comprises the following steps:
1. The receiver (i.e., the initiator) creates a 1. The receiver (i.e., the initiator) creates a
return_routability_check message of type path_challenge and return_routability_check message of type path_challenge and
places the unpredictable cookie into the message. places the unpredictable cookie into the message.
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3. The peer (i.e., the responder) cryptographically verifies the 3. The peer (i.e., the responder) cryptographically verifies the
received return_routability_check message of type path_challenge received return_routability_check message of type path_challenge
and responds by echoing the cookie value in a and responds by echoing the cookie value in a
return_routability_check message of type path_response. return_routability_check message of type path_response.
4. When the initiator receives the return_routability_check message 4. When the initiator receives the return_routability_check message
of type path_response and verifies that it contains the sent of type path_response and verifies that it contains the sent
cookie, it updates the peer address binding. cookie, it updates the peer address binding.
5. If T expires the peer address binding is not updated. 5. If T expires, the peer address binding is not updated.
5.2. Enhanced 5.2. Enhanced
The enhanced return routability check comprises the following steps: The enhanced return routability check comprises the following steps:
1. The receiver (i.e., the initiator) creates a 1. The receiver (i.e., the initiator) creates a
return_routability_check message of type path_challenge and return_routability_check message of type path_challenge and
places the unpredictable cookie into the message. places the unpredictable cookie into the message.
2. The message is sent to the previously valid address, which 2. The message is sent to the previously valid address, which
corresponds to the old path. Additionally, a timer T is started, corresponds to the old path. Additionally, a timer T is started
see Section 5.5. (see Section 5.5).
3. If the path is still functional, the peer (i.e., the responder) 3. If the path is still functional, the peer (i.e., the responder)
cryptographically verifies the received return_routability_check cryptographically verifies the received return_routability_check
message of type path_challenge. The action to be taken depends message of type path_challenge. The action to be taken depends
on whether the path through which the message was received on whether the path through which the message was received
remains the preferred one. remains the preferred one.
* If the path through which the message was received is * If the path through which the message was received is
preferred, a return_routability_check message of type preferred, a return_routability_check message of type
path_response MUST be returned. (Note that, from the path_response MUST be returned. (Note that, from the
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that this path is no longer the preferred one.) that this path is no longer the preferred one.)
In either case, the peer echoes the cookie value in the response. In either case, the peer echoes the cookie value in the response.
4. The initiator receives and verifies that the 4. The initiator receives and verifies that the
return_routability_check message contains the previously sent return_routability_check message contains the previously sent
cookie. The actions taken by the initiator differ based on the cookie. The actions taken by the initiator differ based on the
received message: received message:
* When a return_routability_check message of type path_response * When a return_routability_check message of type path_response
was received, the initiator MUST continue using the previously is received, the initiator MUST continue using the previously
valid address, i.e., no switch to the new path takes place and valid address, i.e., no switch to the new path takes place and
the peer address binding is not updated. the peer address binding is not updated.
* When a return_routability_check message of type path_drop was * When a return_routability_check message of type path_drop is
received, the initiator MUST perform a return routability received, the initiator MUST perform a return routability
check on the observed new address, as described in check on the observed new address, as described in
Section 5.1. Section 5.1.
5. If T expires the peer address binding is not updated. In this 5. If T expires, the peer address binding is not updated. In this
case, the initiator MUST perform a return routability check on case, the initiator MUST perform a return routability check on
the observed new address, as described in Section 5.1. the observed new address, as described in Section 5.1.
5.3. Path Challenge Requirements 5.3. Path Challenge Requirements
* The initiator MAY send multiple return_routability_check messages * The initiator MAY send multiple return_routability_check messages
of type path_challenge to cater for packet loss on the probed of type path_challenge to cater for packet loss on the probed
path. path.
- Each path_challenge SHOULD go into different transport packets. - Each path_challenge SHOULD go into different transport packets.
(Note that the DTLS implementation may not have control over (Note that the DTLS implementation may not have control over
the packetization done by the transport layer.) the packetization done by the transport layer.)
- The transmission of subsequent path_challenge messages SHOULD - The transmission of subsequent path_challenge messages SHOULD
be paced to decrease the chance of loss. be paced to decrease the chance of loss.
- Each path_challenge message MUST contain random data. - Each path_challenge message MUST contain random data.
- In general, the number of "backup" path_challenge messages - In general, the number of "backup" path_challenge messages
depends on the application, since some are more sensitive to depends on the application, since some are more sensitive than
latency caused by changes in the path than others. In the others to latency caused by changes in the path. In the
absence of application-specific requirements, the initiator can absence of application-specific requirements, the initiator can
send a path_challenge message once per round-trip time (RTT), send a path_challenge message once per round-trip time (RTT),
up to the anti-amplification limit. up to the anti-amplification limit.
* The initiator MAY use padding using the record padding mechanism * The initiator MAY use padding using the record padding mechanism
available in DTLS 1.3 (and in DTLS 1.2, when CID is enabled on the available in DTLS 1.3 (and in DTLS 1.2, when CID is enabled on the
sending direction) up to the anti-amplification limit to probe if sending direction) up to the anti-amplification limit to probe if
the path MTU (PMTU) for the new path is still acceptable. the Path MTU (PMTU) for the new path is still acceptable.
5.4. Path Response/Drop Requirements 5.4. Path Response/Drop Requirements
* The responder MUST NOT delay sending an elicited path_response or * The responder MUST NOT delay sending an elicited path_response or
path_drop messages. path_drop messages.
* The responder MUST send exactly one path_response or path_drop * The responder MUST send exactly one path_response or path_drop
message for each valid path_challenge it received. message for each valid path_challenge it received.
* The responder MUST send the path_response or the path_drop to the * The responder MUST send the path_response or the path_drop to the
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5.5. Timer Choice 5.5. Timer Choice
When setting T, implementations are cautioned that the new path could When setting T, implementations are cautioned that the new path could
have a longer RTT than the original. have a longer RTT than the original.
In settings where there is external information about the RTT of the In settings where there is external information about the RTT of the
active path (i.e., the old path), implementations SHOULD use T = active path (i.e., the old path), implementations SHOULD use T =
3xRTT. 3xRTT.
If an implementation has no way to obtain information regarding the If an implementation has no way to obtain information regarding the
RTT of the active path, T SHOULD be set to 1s. RTT of the active path, T SHOULD be set to 1 second.
Profiles for specific deployment environments -- for example, Profiles for specific deployment environments -- for example,
constrained networks [I-D.ietf-uta-tls13-iot-profile] -- MAY specify constrained networks [IOT-PROFILE] -- MAY specify a different, more
a different, more suitable value for T. suitable value for T.
6. Example 6. Example
Figure 2 shows an example of a DTLS 1.3 handshake in which a client Figure 2 shows an example of a DTLS 1.3 handshake in which a client
and a server successfully negotiate support for both the CID and RRC and a server successfully negotiate support for both the CID and RRC
extensions. extensions.
Client Server Client Server
Key ^ ClientHello Key ^ ClientHello
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derived from [sender]_application_traffic_secret_N. derived from [sender]_application_traffic_secret_N.
Figure 2: Message Flow for Full DTLS Handshake Figure 2: Message Flow for Full DTLS Handshake
Once a connection has been established, the client and the server Once a connection has been established, the client and the server
exchange application payloads protected by DTLS with a unilaterally exchange application payloads protected by DTLS with a unilaterally
used CID. In this case, the client is requested to use CID 100 for used CID. In this case, the client is requested to use CID 100 for
records sent to the server. records sent to the server.
At some point in the communication interaction, the address used by At some point in the communication interaction, the address used by
the client changes and, thanks to the CID usage, the security context the client changes, and thanks to the CID usage, the security context
to interpret the record is successfully located by the server. to interpret the record is successfully located by the server.
However, the server wants to test the reachability of the client at However, the server wants to test the reachability of the client at
its new address. its new address.
Figure 3 shows the server initiating a "basic" RRC exchange (see Figure 3 shows the server initiating a basic RRC exchange (see
Section 5.1) that establishes reachability of the client at the new Section 5.1) that establishes reachability of the client at the new
address. address.
Client Server Client Server
------ ------ ------ ------
Application Data ========> Application Data ========>
<CID=100> <CID=100>
Src-IP=A Src-IP=A
Dst-IP=Z Dst-IP=Z
skipping to change at page 11, line 47 skipping to change at line 502
Src-IP=B Src-IP=B
Dst-IP=Z Dst-IP=Z
<<< IP Address B <<< IP Address B
Verified >> Verified >>
<======== Application Data <======== Application Data
Src-IP=Z Src-IP=Z
Dst-IP=B Dst-IP=B
Figure 3: "Basic" Return Routability Example Figure 3: Basic Return Routability Example
7. Operational Considerations 7. Operational Considerations
7.1. Logging Anomalous Events 7.1. Logging Anomalous Events
Logging of RRC operations at both ends of the protocol can be Logging of RRC operations at both ends of the protocol can be
generally useful for the users of an implementation. In particular, generally useful for the users of an implementation. In particular,
for security information and event management (SIEM) and for Security Information and Event Management (SIEM) and
troubleshooting purposes, it is strongly advised that implementations troubleshooting purposes, it is strongly advised that implementations
collect statistics about any unsuccessful RRC operations, as they collect statistics about any unsuccessful RRC operations, as they
could represent security-relevant events when they coincide with could represent security-relevant events when they coincide with
attempts by an attacker to interfere with the end-to-end path. It is attempts by an attacker to interfere with the end-to-end path. It is
also advisable to log instances where multiple responses to a single also advisable to log instances where multiple responses to a single
path_challenge are received, as this could suggest an off-path attack path_challenge are received, as this could suggest an off-path attack
attempt. attempt.
In some cases, the presence of frequent path probes could indicate a In some cases, the presence of frequent path probes could indicate a
problem with the stability of the path. This information can be used problem with the stability of the path. This information can be used
skipping to change at page 12, line 31 skipping to change at line 533
7.2. Middlebox Interference 7.2. Middlebox Interference
Since the DTLS 1.3 encrypted packet's record type is opaque to on- Since the DTLS 1.3 encrypted packet's record type is opaque to on-
path observers, RRC messages are immune to middlebox interference path observers, RRC messages are immune to middlebox interference
when using DTLS 1.3. In contrast, DTLS 1.2 RRC messages that are not when using DTLS 1.3. In contrast, DTLS 1.2 RRC messages that are not
wrapped in the tls12_cid record (e.g., in the server-to-client wrapped in the tls12_cid record (e.g., in the server-to-client
direction if the server negotiated a zero-length CID) have the direction if the server negotiated a zero-length CID) have the
return_routability_check content type in plain text, making them return_routability_check content type in plain text, making them
susceptible to interference (e.g., dropping of path_challenge susceptible to interference (e.g., dropping of path_challenge
messages), which would hinder the RRC functionality altogether. messages), which would hinder the RRC functionality altogether.
Therefore, when using RRC in DTLS 1.2 and middlebox interference is a Therefore, when RRC in DTLS 1.2 is used and middlebox interference is
concern, it is recommended to enable CID in both directions. a concern, it is recommended to enable CID in both directions.
8. Security Considerations 8. Security Considerations
Note that the return routability checks do not protect against Note that the return routability checks do not protect against
flooding of third-parties if the attacker is on-path, as the attacker flooding of third parties if the attacker is on-path, as the attacker
can redirect the return routability checks to the real peer (even if can redirect the return routability checks to the real peer (even if
those datagrams are cryptographically authenticated). On-path those datagrams are cryptographically authenticated). On-path
adversaries can, in general, pose a harm to connectivity. adversaries can, in general, pose a harm to connectivity.
If the RRC challenger reuses a cookie that was previously used in the If the RRC challenger reuses a cookie that was previously used in the
same connection and does not implement anti-replay protection (see same connection and does not implement anti-replay protection (see
Section 4.5.1 of [RFC9147] and Section 4.1.2.6 of [RFC6347]), an Section 4.5.1 of [RFC9147] and Section 4.1.2.6 of [RFC6347]), an
attacker could replay a previously sent path_response message attacker could replay a previously sent path_response message
containing the reused cookie to mislead the challenger into switching containing the reused cookie to mislead the challenger into switching
to a path of the attacker's choosing. To prevent this, RRC cookies to a path of the attacker's choosing. To prevent this, RRC cookies
must be _freshly_ generated using a reliable source of entropy must be _freshly_ generated using a reliable source of entropy
[RFC4086]. See Appendix C.1 of [RFC8446] for guidance. [RFC4086]. See Appendix C.1 of [RFC8446] for guidance.
8.1. Attacker Model 8.1. Attacker Model
Two classes of attackers are considered, off-path and on-path, with Two classes of attackers are considered, off-path and on-path, with
increasing capabilities (see Figure 4) partly following terminology increasing capabilities (see Figure 4) partly following terminology
introduced in QUIC (Section 21.1 of [RFC9000]): introduced in QUIC (Section 21.1 of [RFC9000]):
* An off-path attacker is not on the original path between the DTLS * An off-path attacker is not on the original path between the DTLS
peers, but is able to observe packets on the original path and has peers, but it is able to observe packets on the original path and
a faster forwarding path compared to the DTLS peers, which allows has a faster forwarding path compared to the DTLS peers, which
it to make copies of the observed packets, race its copies to allows it to make copies of the observed packets, race its copies
either peer and consistently win the race. to either peer, and consistently win the race.
* An on-path attacker is on the original path between the DTLS peers * An on-path attacker is on the original path between the DTLS peers
and is therefore capable, compared to the off-path attacker, to and is therefore capable, compared to the off-path attacker, to
also drop and delay records at will. also drop and delay records at will.
Note that, in general, attackers cannot craft DTLS records in a way Note that, in general, attackers cannot craft DTLS records in a way
that would successfully pass verification, due to the cryptographic that would successfully pass verification, due to the cryptographic
protections applied by the DTLS record layer. protections applied by the DTLS record layer.
.--> .------------------------------------. <--. .--> .------------------------------------. <--.
| | Inspect un-encrypted portions | | | | Inspect unencrypted portions | |
| +------------------------------------+ | | +------------------------------------+ |
| | Inject | | | | Inject | |
off-path +------------------------------------+ | off-path +------------------------------------+ |
| | Reorder | | | | Reorder | |
| +------------------------------------+ | | +------------------------------------+ |
| | Modify un-authenticated portions | on-path | | Modify unauthenticated portions | on-path
'--> +------------------------------------+ | '--> +------------------------------------+ |
| Delay | | | Delay | |
+------------------------------------+ | +------------------------------------+ |
| Drop | | | Drop | |
+------------------------------------+ | +------------------------------------+ |
| Manipulate the packetization layer | | | Manipulate the packetization layer | |
'------------------------------------' <--' '------------------------------------' <--'
Figure 4: Attacker capabilities Figure 4: Attacker Capabilities
RRC is designed to defend against the following attacks: RRC is designed to defend against the following attacks:
* On-path and off-path attackers that try to create an amplification * On-path and off-path attackers that try to create an amplification
attack by spoofing the source address of the victim attack by spoofing the source address of the victim
(Section 8.1.1). (Section 8.1.1).
* Off-path attackers that try to put themselves on-path * Off-path attackers that try to put themselves on-path
(Section 8.1.2), provided that the enhanced path validation (Section 8.1.2), provided that the enhanced path validation
algorithm is used (Section 5.2). algorithm is used (Section 5.2).
8.1.1. Amplification 8.1.1. Amplification
Both on-path and off-path attackers can send a packet (either by Both on-path and off-path attackers can send a packet (either by
modifying it on the fly, or by copying, injecting, and racing it, modifying it on the fly or by copying, injecting, and racing it,
respectively) with the source address modified to that of a victim respectively) with the source address modified to that of a victim
host. If the traffic generated by the server in response is larger host. If the traffic generated by the server in response is larger
compared to the received packet (e.g., a CoAP server returning an compared to the received packet (e.g., a CoAP server returning an
MTU's worth of data from a 20-bytes GET request MTU's worth of data from a 20-byte GET request [AMP-ATTACKS]), the
[I-D.irtf-t2trg-amplification-attacks]) the attacker can use the attacker can use the server as a traffic amplifier toward the victim.
server as a traffic amplifier toward the victim.
8.1.1.1. Mitigation Strategy 8.1.1.1. Mitigation Strategy
When receiving a packet with a known CID that has a source address When receiving a packet with a known CID that has a source address
different from the one currently associated with the DTLS connection, different from the one currently associated with the DTLS connection,
an RRC-capable endpoint will not send a (potentially large) response an RRC-capable endpoint will not send a (potentially large) response
but instead a small path_challenge message to the victim host. Since but instead a small path_challenge message to the victim host. Since
the host is not able to decrypt it and generate a valid the host is not able to decrypt it and generate a valid
path_response, the address validation fails, which in turn keeps the path_response, the address validation fails, which in turn keeps the
original address binding unaltered. original address binding unaltered.
Note that in case of an off-path attacker, the original packet still Note that in the case of an off-path attacker, the original packet
reaches the intended destination; therefore, an implementation could still reaches the intended destination; therefore, an implementation
use a different strategy to mitigate the attack. could use a different strategy to mitigate the attack.
8.1.2. Off-Path Packet Forwarding 8.1.2. Off-Path Packet Forwarding
An off-path attacker that can observe packets might forward copies of An off-path attacker that can observe packets might forward copies of
genuine packets to endpoints over a different path. If the copied genuine packets to endpoints over a different path. If the copied
packet arrives before the genuine packet, this will appear as a path packet arrives before the genuine packet, this will appear as a path
change, like in a genuine NAT rebinding occurrence. Any genuine change, like in a genuine NAT rebinding occurrence. Any genuine
packet will be discarded as a duplicate. If the attacker is able to packet will be discarded as a duplicate. If the attacker is able to
continue forwarding packets, it might be able to cause migration to a continue forwarding packets, it might be able to cause migration to a
path via the attacker. This places the attacker on-path, giving it path via the attacker. This places the attacker on-path, giving it
skipping to change at page 14, line 50 skipping to change at line 645
This style of attack relies on the attacker using a path that has the This style of attack relies on the attacker using a path that has the
same or better characteristics (e.g., due to a more favourable same or better characteristics (e.g., due to a more favourable
service level agreements) as the direct path between endpoints. The service level agreements) as the direct path between endpoints. The
attack is more effective if relatively few packets are sent or if attack is more effective if relatively few packets are sent or if
packet loss coincides with the attempted attack. packet loss coincides with the attempted attack.
A data packet received on the original path that increases the A data packet received on the original path that increases the
maximum received packet number will cause the endpoint to move back maximum received packet number will cause the endpoint to move back
to that path. Therefore, eliciting packets on this path increases to that path. Therefore, eliciting packets on this path increases
the likelihood that the attack is unsuccessful. Note however that, the likelihood that the attack is unsuccessful. However, note that,
unlike QUIC, DTLS has no "non-probing" packets so this would require unlike QUIC, DTLS has no "non-probing" packets so this would require
application specific mechanisms. application-specific mechanisms.
8.1.2.1. Mitigation Strategy 8.1.2.1. Mitigation Strategy
Figure 5 illustrates the case where a receiver receives a packet with Figure 5 illustrates the case where a receiver receives a packet with
a new source address. In order to determine that this path change a new source address. In order to determine that this path change
was not triggered by an off-path attacker, the receiver will send an was not triggered by an off-path attacker, the receiver will send an
RRC message of type path_challenge (1) on the old path. RRC message of type path_challenge (1) on the old path.
new old new old
path .----------. path path .----------. path
skipping to change at page 16, line 26 skipping to change at line 709
'----|-+-|-----------------------' '----|-+-|-----------------------'
| | | . | | | .
| | 2 path- . | | 2 path- .
| | | challenge . | | | challenge .
| | | .----------. . | | | .----------. .
| | '-->| | . | | '-->| | .
| '-----+ Sender +.....' | '-----+ Sender +.....'
'-------+ | '-------+ |
'----------' '----------'
Figure 6: Old path is dead Figure 6: Old Path Is Dead
Case 2: The old path is alive but not preferred. Case 2: The old path is alive but not preferred.
This case is shown in Figure 7 whereby the sender replies with a This case is shown in Figure 7 whereby the sender replies with a
path_drop message (2) on the old path. This triggers the receiver to path_drop message (2) on the old path. This triggers the receiver to
send a path_challenge (3) on the new path. The sender will reply send a path_challenge (3) on the new path. The sender will reply
with a path_response (4) on the new path, thus providing confirmation with a path_response (4) on the new path, thus providing confirmation
for the path migration. for the path migration.
new old new old
skipping to change at page 17, line 26 skipping to change at line 740
'-----------|---|--' '----|-+-|---------' '-----------|---|--' '----|-+-|---------'
| | | | | | | | | | | |
| | 3 path- | | 2 path- | | 3 path- | | 2 path-
| | | challenge | | | drop | | | challenge | | | drop
| | | .----------. | | | | | | .----------. | | |
| | '-->| |<--' | | | | '-->| |<--' | |
| '-----+ Sender +-----' | | '-----+ Sender +-----' |
'-------+ +-------' '-------+ +-------'
'----------' '----------'
Figure 7: Old path is not preferred Figure 7: Old Path Is Not Preferred
Case 3: The old path is alive and preferred. Case 3: The old path is alive and preferred.
This is most likely the result of an off-path attacker trying to This is most likely the result of an off-path attacker trying to
place itself on path. The receiver sends a path_challenge on the old place itself on-path. As shown in Figure 8, the receiver sends a
path and the sender replies with a path_response (2) on the old path. path_challenge on the old path, and the sender replies with a
The interaction is shown in Figure 8. This results in the connection path_response (2) on the old path. This results in the connection
not being migrated to the new path, thus thwarting the attack. not being migrated to the new path, thus thwarting the attack.
new old new old
path .----------. path path .----------. path
| +-------. | +-------.
.-----+ Receiver +-----. | .-----+ Receiver +-----. |
| | |<--. | | | | |<--. | |
| '----------' | | | | '----------' | | |
| | | 1 path- | | | 1 path-
| | | | challenge | | | | challenge
skipping to change at page 18, line 27 skipping to change at line 772
'------+---' | | | '------+---' | | |
| | | | | | | |
| path- 2 | | | path- 2 | |
| response | | | | response | | |
| .----------. | | | | .----------. | | |
| | +---' | | | | +---' | |
'-----+ Sender +-----' | '-----+ Sender +-----' |
| |<------' | |<------'
'----------' '----------'
Figure 8: Old path is preferred Figure 8: Old Path Is Preferred
Note that this defense is imperfect, but this is not considered a Note that this defense is imperfect, but this is not considered a
serious problem. If the path via the attacker is reliably faster serious problem. If the path via the attacker is reliably faster
than the old path despite multiple attempts to use that old path, it than the old path despite multiple attempts to use that old path, it
is not possible to distinguish between an attack and an improvement is not possible to distinguish between an attack and an improvement
in routing. in routing.
An endpoint could also use heuristics to improve detection of this An endpoint could also use heuristics to improve detection of this
style of attack. For instance, NAT rebinding is improbable if style of attack. For instance, NAT rebinding is improbable if
packets were recently received on the old path. Endpoints can also packets were recently received on the old path. Endpoints can also
look for duplicated packets. Conversely, a change in connection ID look for duplicated packets. Conversely, a change in CID is more
is more likely to indicate an intentional migration rather than an likely to indicate an intentional migration rather than an attack.
attack. Note that changes in connection IDs are supported in DTLS Note that changes in CIDs are supported in DTLS 1.3 but not in DTLS
1.3 but not in DTLS 1.2. 1.2.
9. Privacy Considerations 9. Privacy Considerations
When using DTLS 1.3, peers SHOULD avoid using the same CID on When using DTLS 1.3, peers SHOULD avoid using the same CID on
multiple network paths, in particular when initiating connection multiple network paths, in particular when initiating connection
migration or when probing a new network path, as described in migration or when probing a new network path, as described in
Section 5, as an adversary can otherwise correlate the communication Section 5, as an adversary can otherwise correlate the communication
interaction across those different paths. DTLS 1.3 provides interaction across those different paths. DTLS 1.3 provides
mechanisms to ensure that a new CID can always be used. In general, mechanisms to ensure that a new CID can always be used. In general,
an endpoint should proactively send a RequestConnectionId message to an endpoint should proactively send a RequestConnectionId message to
ask for new CIDs as soon as the pool of spare CIDs is depleted (or ask for new CIDs as soon as the pool of spare CIDs is depleted (or
goes below a threshold). Also, in case a peer might have exhausted goes below a threshold). Also, in case a peer might have exhausted
available CIDs, a migrating endpoint could include NewConnectionId in available CIDs, a migrating endpoint could include NewConnectionId in
packets sent on the new path to make sure that the subsequent path packets sent on the new path to make sure that the subsequent path
validation can use fresh CIDs. validation can use fresh CIDs.
Note that DTLS 1.2 does not offer the ability to request new CIDs Note that DTLS 1.2 does not offer the ability to request new CIDs
during the session lifetime since CIDs have the same life-span of the during the session lifetime since CIDs have the same lifespan of the
connection. Therefore, deployments that use DTLS in multihoming connection. Therefore, deployments that use DTLS in multihoming
environments SHOULD refuse to use CIDs with DTLS 1.2 and switch to environments SHOULD refuse to use CIDs with DTLS 1.2 and switch to
DTLS 1.3 if the correlation privacy threat is a concern. DTLS 1.3 if the correlation privacy threat is a concern.
10. IANA Considerations 10. IANA Considerations
// RFC Editor: please replace RFCthis with this RFC number and remove
// this note.
10.1. New TLS ContentType 10.1. New TLS ContentType
IANA is requested to allocate an entry in the TLS ContentType IANA has allocated an entry in the "TLS ContentType" registry within
registry within the "Transport Layer Security (TLS) Parameters" the "Transport Layer Security (TLS) Parameters" registry group
registry group [IANA.tls-parameters] for the [IANA.tls-parameters] for the return_routability_check (27) message
return_routability_check(TBD2) message defined in this document. defined in this document. IANA set the DTLS_OK column to "Y" and
IANA is requested to set the DTLS_OK column to Y and to add the added the following note to the registry:
following note prior to the table:
NOTE: The return_routability_check content type is only applicable | Note: The return_routability_check content type is only applicable
to DTLS 1.2 and 1.3. | to DTLS 1.2 and 1.3.
10.2. New TLS ExtensionType 10.2. New TLS ExtensionType
IANA is requested to allocate the extension code point (TBD1) for the IANA has allocated the extension code point (61) for rrc in the "TLS
rrc extension to the TLS ExtensionType Values registry as described ExtensionType Values" registry as described in Table 1.
in Table 1.
+=====+=========+===+===========+=============+===========+=======+ +=====+=========+===+===========+=============+===========+=======+
|Value|Extension|TLS| DTLS-Only | Recommended | Reference |Comment| |Value|Extension|TLS| DTLS-Only | Recommended | Reference |Comment|
| |Name |1.3| | | | | | |Name |1.3| | | | |
+=====+=========+===+===========+=============+===========+=======+ +=====+=========+===+===========+=============+===========+=======+
|TBD1 |rrc |CH,| Y | N | RFCthis | | |61 |rrc |CH,| Y | N | RFC 9853 | |
| | |SH | | | | | | | |SH | | | | |
+-----+---------+---+-----------+-------------+-----------+-------+ +-----+---------+---+-----------+-------------+-----------+-------+
Table 1: rrc entry in the TLS ExtensionType Values registry Table 1: New Entry in the TLS ExtensionType Values Registry
10.3. New "TLS RRC Message Type" Registry 10.3. New "TLS RRC Message Type" Registry
IANA is requested to create a new registry "TLS RRC Message Types" IANA has created the "TLS RRC Message Types" registry within the
within the Transport Layer Security (TLS) Parameters registry group "Transport Layer Security (TLS) Parameters" registry group
[IANA.tls-parameters]. This registry will be administered under the [IANA.tls-parameters]. This registration procedure is "Expert
"Expert Review" policy (Section 4.5 of [RFC8126]). Review" (Section 4.5 of [RFC8126]).
Follow the procedures in Section 16 of [I-D.ietf-tls-rfc8447bis] to To submit registration requests, follow the procedures in Section 16
submit registration requests. of [RFC9847].
Each entry in the registry must include the following fields: Each entry in the registry must include the following fields:
Value: Value:
A (decimal) number in the range 0 to 253 A (decimal) number in the range 0 to 253.
Description: Description:
A brief description of the RRC message A brief description of the RRC message.
DTLS-Only: DTLS-Only:
Whether the message applies only to DTLS. Since RRC is only Indication of whether the message only applies to DTLS. Since RRC
available in DTLS, this column will be set to Y for all the is only available in DTLS, this column is set to "Y" for all the
current entries in this registry. Future work may define new RRC initial entries in this registry. Future work may define new RRC
Message Types that also apply to TLS. message types that also apply to TLS.
Recommended: Recommended:
Whether the message is recommended for implementations to support. Indication of whether the message is recommended for
The semantics for this field is defined in Section 5 of [RFC8447] implementations to support. The semantics for this field is
and updated in Section 3 of [I-D.ietf-tls-rfc8447bis] defined in Section 5 of [RFC8447] and updated in Section 3 of
[RFC9847].
Reference: Reference:
A reference to a publicly available specification for the value A reference to a publicly available specification for the value.
Comment: Comment:
Any relevant notes or comments that relate to this entry Any relevant notes or comments that relate to this entry.
The initial state of this sub-registry is as follows: Table 2 shows the initial contents of this registry:
+=======+================+=========+=============+=========+=======+ +=======+================+=========+=============+=========+=======+
|Value | Description |DTLS-Only| Recommended |Reference|Comment| |Value | Description |DTLS-Only| Recommended |Reference|Comment|
+=======+================+=========+=============+=========+=======+ +=======+================+=========+=============+=========+=======+
|0 | path_challenge |Y | Y |RFCthis | | |0 | path_challenge |Y | Y |RFC 9853 | |
+-------+----------------+---------+-------------+---------+-------+ +-------+----------------+---------+-------------+---------+-------+
|1 | path_response |Y | Y |RFCthis | | |1 | path_response |Y | Y |RFC 9853 | |
+-------+----------------+---------+-------------+---------+-------+ +-------+----------------+---------+-------------+---------+-------+
|2 | path_drop |Y | Y |RFCthis | | |2 | path_drop |Y | Y |RFC 9853 | |
+-------+----------------+---------+-------------+---------+-------+ +-------+----------------+---------+-------------+---------+-------+
|3-253 | Unassigned | | | | | |3-253 | Unassigned | | | | |
+-------+----------------+---------+-------------+---------+-------+ +-------+----------------+---------+-------------+---------+-------+
|254-255| Reserved for |Y | |RFCthis | | |254-255| Reserved for |Y | |RFC 9853 | |
| | Private Use | | | | | | | Private Use | | | | |
+-------+----------------+---------+-------------+---------+-------+ +-------+----------------+---------+-------------+---------+-------+
Table 2: Initial Entries in TLS RRC Message Type registry Table 2: Initial Entries in TLS RRC Message Type Registry
IANA is requested to add the following note for additional IANA added the following note to provide additional information
information regarding the use of RRC message codepoints in regarding the use of RRC message codepoints in experiments:
experiments:
Note: As specified in [RFC8126], assignments made in the Private Use | Note: As specified in [RFC8126], assignments made in the Private
space are not generally useful for broad interoperability. Those | Use space are not generally useful for broad interoperability.
making use of the Private Use range are responsible for ensuring | Those making use of the Private Use range are responsible for
that no conflicts occur within the intended scope of use. For | ensuring that no conflicts occur within the intended scope of use.
widespread experiments, provisional registrations (Section 4.13 of | For widespread experiments, provisional registrations
[RFC8126]) are available. | (Section 4.13 of [RFC8126]) are available.
10.3.1. Designated Expert Instructions 10.3.1. Designated Expert Instructions
To enable a broadly informed review of registration decisions, it is To enable a broadly informed review of registration decisions, it is
recommended that multiple Designated Experts be appointed who are recommended that multiple designated experts be appointed to
able to represent the perspectives of both the transport and security represent the perspectives of both the transport and security areas.
areas.
In cases where a registration decision could be perceived as creating In cases where a registration decision could be perceived as creating
a conflict of interest for a particular Expert, that Expert SHOULD a conflict of interest for a particular expert, that expert SHOULD
defer to the judgment of the other Experts. defer to the judgment of the other experts.
11. Acknowledgments
We would like to thank Colin Perkins, Deb Cooley, Eric Rescorla, Éric
Vyncke, Erik Kline, Hanno Becker, Hanno Böck, Joe Clarke, Manuel
Pégourié-Gonnard, Marco Tiloca, Martin Thomson, Mike Bishop, Mike
Ounsworth, Mohamed Boucadair, Mohit Sahni, Rich Salz, Russ Housley,
Sean Turner, and Yaron Sheffer for their input to this document.
12. References 11. References
12.1. Normative References
[I-D.ietf-tls-rfc8447bis] 11.1. Normative References
Salowey, J. A. and S. Turner, "IANA Registry Updates for
TLS and DTLS", Work in Progress, Internet-Draft, draft-
ietf-tls-rfc8447bis-14, 16 June 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
rfc8447bis-14>.
[IANA.tls-parameters] [IANA.tls-parameters]
IANA, "Transport Layer Security (TLS) Parameters", IANA, "Transport Layer Security (TLS) Parameters",
<https://www.iana.org/assignments/tls-parameters>. <https://www.iana.org/assignments/tls-parameters>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer [RFC6347] Rescorla, E. and N. Modadugu, "Datagram Transport Layer
Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
January 2012, <https://www.rfc-editor.org/rfc/rfc6347>. January 2012, <https://www.rfc-editor.org/info/rfc6347>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/rfc/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS [RFC8447] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018, and DTLS", RFC 8447, DOI 10.17487/RFC8447, August 2018,
<https://www.rfc-editor.org/rfc/rfc8447>. <https://www.rfc-editor.org/info/rfc8447>.
[RFC9146] Rescorla, E., Ed., Tschofenig, H., Ed., Fossati, T., and [RFC9146] Rescorla, E., Ed., Tschofenig, H., Ed., Fossati, T., and
A. Kraus, "Connection Identifier for DTLS 1.2", RFC 9146, A. Kraus, "Connection Identifier for DTLS 1.2", RFC 9146,
DOI 10.17487/RFC9146, March 2022, DOI 10.17487/RFC9146, March 2022,
<https://www.rfc-editor.org/rfc/rfc9146>. <https://www.rfc-editor.org/info/rfc9146>.
[RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The [RFC9147] Rescorla, E., Tschofenig, H., and N. Modadugu, "The
Datagram Transport Layer Security (DTLS) Protocol Version Datagram Transport Layer Security (DTLS) Protocol Version
1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022, 1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
<https://www.rfc-editor.org/rfc/rfc9147>. <https://www.rfc-editor.org/info/rfc9147>.
12.2. Informative References [RFC9847] Salowey, J. and S. Turner, "IANA Registry Updates for TLS
and DTLS", RFC 9847, DOI 10.17487/RFC9847, December 2025,
<https://www.rfc-editor.org/info/rfc9847>.
[I-D.ietf-uta-tls13-iot-profile] 11.2. Informative References
Tschofenig, H., Fossati, T., and M. Richardson, "TLS/DTLS
1.3 Profiles for the Internet of Things", Work in
Progress, Internet-Draft, draft-ietf-uta-tls13-iot-
profile-14, 5 May 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
tls13-iot-profile-14>.
[I-D.irtf-t2trg-amplification-attacks] [AMP-ATTACKS]
Mattsson, J. P., Selander, G., and C. Amsüss, Preuß Mattsson, J., Selander, G., and C. Amsüss,
"Amplification Attacks Using the Constrained Application "Amplification Attacks Using the Constrained Application
Protocol (CoAP)", Work in Progress, Internet-Draft, draft- Protocol (CoAP)", Work in Progress, Internet-Draft, draft-
irtf-t2trg-amplification-attacks-05, 18 June 2025, irtf-t2trg-amplification-attacks-05, 18 June 2025,
<https://datatracker.ietf.org/doc/html/draft-irtf-t2trg- <https://datatracker.ietf.org/doc/html/draft-irtf-t2trg-
amplification-attacks-05>. amplification-attacks-05>.
[IOT-PROFILE]
Tschofenig, H., Fossati, T., and M. Richardson, "TLS/DTLS
1.3 Profiles for the Internet of Things", Work in
Progress, Internet-Draft, draft-ietf-uta-tls13-iot-
profile-18, 3 February 2026,
<https://datatracker.ietf.org/doc/html/draft-ietf-uta-
tls13-iot-profile-18>.
[RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker, [RFC4086] Eastlake 3rd, D., Schiller, J., and S. Crocker,
"Randomness Requirements for Security", BCP 106, RFC 4086, "Randomness Requirements for Security", BCP 106, RFC 4086,
DOI 10.17487/RFC4086, June 2005, DOI 10.17487/RFC4086, June 2005,
<https://www.rfc-editor.org/rfc/rfc4086>. <https://www.rfc-editor.org/info/rfc4086>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based [RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000, Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021, DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/rfc/rfc9000>. <https://www.rfc-editor.org/info/rfc9000>.
[RFC9175] Amsüss, C., Preuß Mattsson, J., and G. Selander, [RFC9175] Amsüss, C., Preuß Mattsson, J., and G. Selander,
"Constrained Application Protocol (CoAP): Echo, Request- "Constrained Application Protocol (CoAP): Echo, Request-
Tag, and Token Processing", RFC 9175, Tag, and Token Processing", RFC 9175,
DOI 10.17487/RFC9175, February 2022, DOI 10.17487/RFC9175, February 2022,
<https://www.rfc-editor.org/rfc/rfc9175>. <https://www.rfc-editor.org/info/rfc9175>.
Acknowledgments
We would like to thank Colin Perkins, Deb Cooley, Eric Rescorla, Éric
Vyncke, Erik Kline, Hanno Becker, Hanno Böck, Joe Clarke, Manuel
Pégourié-Gonnard, Marco Tiloca, Martin Thomson, Mike Bishop, Mike
Ounsworth, Mohamed Boucadair, Mohit Sahni, Rich Salz, Russ Housley,
Sean Turner, and Yaron Sheffer for their input to this document.
Authors' Addresses Authors' Addresses
Hannes Tschofenig (editor) Hannes Tschofenig (editor)
University of Applied Sciences Bonn-Rhein-Sieg University of Applied Sciences Bonn-Rhein-Sieg
Email: Hannes.Tschofenig@gmx.net Email: Hannes.Tschofenig@gmx.net
Achim Kraus Achim Kraus
Email: achimkraus@gmx.net Email: achimkraus@gmx.net
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