Authors,
While reviewing this document during AUTH48, please resolve (as necessary)
the following questions, which are also in the source file.
1) <!-- [rfced] Because this document updates RFC 9147, please
review the errata reported for RFC 9147
(https://www.rfc-editor.org/errata/rfc9147)
and let us know if you confirm our opinion that none of them
are relevant to the content of this document.
-->
2) <!-- [rfced] Please note that the title of the document has been updated
as follows.
Original:
Return Routability Check for DTLS 1.2 and DTLS 1.3
Current:
Return Routability Check for DTLS 1.2 and 1.3
-->
3) <!-- [rfced] Is this sentence in the abstract correct as is, or should
it include the word "subprotocol" (which is used in a similar sentence in
the Introduction)?
Original:
This document specifies a return routability check for use in context
of the Connection ID (CID) construct for the Datagram Transport Layer
Security (DTLS) protocol versions 1.2 and 1.3.
Current:
This document specifies a Return Routability Check (RRC) for use in
the context of the Connection ID (CID) construct for the Datagram
Transport Layer Security (DTLS) protocol versions 1.2 and 1.3.
Perhaps:
This document specifies a Return Routability Check (RRC) subprotocol for
use in the context of the Connection ID (CID) construct for the Datagram
Transport Layer Security (DTLS) protocol versions 1.2 and 1.3.
-->
4) <!-- [rfced] Should "return routability check" here be updated to "basic
return routability check" in these instances in Section 5.2?
Original:
* When a return_routability_check message of type path_drop was
received, the initiator MUST perform a return routability
check on the observed new address, as described in
Section 5.1.
...
5. If T expires the peer address binding is not updated. In this
case, the initiator MUST perform a return routability check on
the observed new address, as described in Section 5.1.
Perhaps:
* When a return_routability_check message of type path_drop was
received, the initiator MUST perform a basic return routability
check on the observed new address, as described in
Section 5.1.
...
5. If T expires the peer address binding is not updated. In this
case, the initiator MUST perform a basic return routability check on
the observed new address, as described in Section 5.1.
-->
5) <!-- [rfced] For clarity, may we update "cater for"?
Original:
* The initiator MAY send multiple return_routability_check messages
of type path_challenge to cater for packet loss on the probed
path.
...
Note that RRC does not cater for PMTU discovery on the reverse path.
Perhaps:
* The initiator MAY send multiple return_routability_check messages
of type path_challenge to account for packet loss on the probed
path.
...
Note that RRC does not account for PMTU discovery on the reverse path.
-->
6) <!-- [rfced] We see the following phrasing with the message types
defined in this document (i.e., path_challenge, path_response, and
path_drop). Please review and let us know if any updates are needed for
consistency.
return_routability_check message of type path_response
return_routability_check message of type path_challenge
return_routability_check message of type path_drop
path_challenge message
path_response message
path_drop message
path_challenge
path_response
path_drop
Some examples:
3. The peer (i.e., the responder) cryptographically verifies the
received return_routability_check message of type path_challenge
and responds by echoing the cookie value in a
return_routability_check message of type path_response.
...
Each path_challenge message MUST contain random data.
...
* The responder MUST send the path_response or the path_drop to the
address from which the corresponding path_challenge was received.
...
-->
7) <!-- [rfced] Please review "use padding using...up to". Would updating
as follows improve readability of this sentence?
Original:
* 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
sending direction) up to the anti-amplification limit to probe if
the path MTU (PMTU) for the new path is still acceptable.
Perhaps:
* The initiator MAY use the record padding mechanism
available in DTLS 1.3 (and in DTLS 1.2, when CID is enabled on the
sending direction) to add padding up to the anti-amplification limit
to probe if the Path MTU (PMTU) for the new path is still acceptable.
-->
8) <!-- [rfced] FYI - We updated "1s" to "1 second" for clarity.
Original:
If an implementation has no way to obtain information regarding the
RTT of the active path, T SHOULD be set to 1s.
Perhaps:
If an implementation has no way to obtain information regarding the
RTT of the active path, T SHOULD be set to 1 second.
-->
9) <!-- [rfced] How may we clarify this sentence, especially "increasing
capabilities" and the text starting with "partly following
terminology..."?
Original:
Two classes of attackers are considered, off-path and on-path, with
increasing capabilities (see Figure 4) partly following terminology
introduced in QUIC (Section 21.1 of [RFC9000]):
Perhaps:
This model includes two classes of attackers, off-path and on-path, with
various capabilities (see Figure 4). The following
descriptions of these attackers are based on those
introduced in QUIC (Section 21.1 of [RFC9000]):
-->
10) <!-- [rfced] Please review the use of "(1)" in the sentences below.
Figure 5 does not include a "1". Should "1" be removed from these sentences
or added to Figure 5? Or does "(1)" in these sentences refer to Figure 6?
Let us know how to clarify. Also, should "timeout of (1)" be updated to
"timeout of the path_challenge message (1)"?
Original:
Figure 5 illustrates the case where a receiver receives a packet with
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
RRC message of type path_challenge (1) on the old path.
<Figure 5>
Case 1: The old path is dead (e.g., due to a NAT rebinding), which
leads to a timeout of (1).
As shown in Figure 6, a path_challenge (2) needs to be sent on the
new path. If the sender replies with a path_response on the new path
(3), the switch to the new path is considered legitimate.
<Figure 6>
-->
11) <!-- [rfced] Would it be helpful to update "path_challenge" here to
"path_challenge (1)"?
Original:
The receiver sends a path_challenge on the old
path and the sender replies with a path_response (2) on the old path.
The interaction is shown in Figure 8.
Perhaps:
As shown in Figure 8, the receiver sends a
path_challenge (1) on the old path, and the sender replies with a
path_response (2) on the old path.
-->
12) <!-- [rfced] Font styling
a) The terms enclosed in <tt> in this document are listed below. Please
review to ensure the usage of <tt> is correct and consistent. Let us know
if any updates are needed. Note that <tt> produces fixed-width font in the
HTML and PDF outputs but no changes in the TXT output.
<tt>connection_id</tt>
<tt>extension_data</tt>
<tt>extension_type</tt>
<tt>msg_type</tt>
<tt>path_challenge</tt>
<tt>path_drop</tt>
<tt>path_response</tt>
<tt>return_routability_check</tt>
<tt>rrc</tt>
<tt>tls12_cid</tt>
b) The following sentence includes <em>, which produces underscores in the
TXT output and italics in the HTML and PDF outputs. Please review to ensure
that this is a correct use of <em>.
Original:
To prevent this, RRC cookies
must be _freshly_ generated using a reliable source of entropy
[RFC4086].
-->
13) <!-- [rfced] Please review the "type" attribute of the sourcecode
element in Section 4, as "tls-msg" is not part of the current list of
preferred values
(https://www.rfc-editor.org/rpc/wiki/doku.php?id=sourcecode-types).
Perhaps "tls-presentation" would be acceptable? This was used for similar
sourcecode in RFCs 9420 and 9458.
If the current list of preferred values for "type" does not contain an
applicable type, then feel free to suggest a new one. Also, it is
acceptable to leave the "type" attribute not set.
-->
14) <!-- [rfced] Terminology
a) We see both "Cookie" and "cookie" used in this document. Should these be
uniform? If so, please let us know which form is preferred.
b) We see the following forms used in the document? Please review and let
us know if any updates are needed for correctness and consistency.
Return Routability Check message
RRC message
return_routability_check message
c) Is "CID-address binding" correct, or should this be updated to "CID
address binding" (no hyphen)?
d) We see that "return routability check" and its acronym "RRC" are used
throughout the document. Would you like to expand the first instance and
then use the acronym in the remainder of the document? Or do you prefer the
current arrangement?
-->
15) <!-- [rfced] FYI - We have added expansions for the following
abbreviations per Section 3.6 of RFC 7322 ("RFC Style Guide"). Please
review each expansion in the document carefully to ensure correctness.
Constrained Application Protocol (CoAP)
cryptographically secure pseudorandom number generator (CSPRNG)
-->
16) <!-- [rfced] Please review the "Inclusive Language" portion of the
online Style Guide
<https://www.rfc-editor.org/styleguide/part2/#inclusive_language>
and let us know if any changes are needed. Updates of this nature typically
result in more precise language, which is helpful for readers.
Note that our script did not flag any words in particular, but this should
still be reviewed as a best practice.
-->
Thank you.
Rebecca VanRheenen and Sandy Ginoza
RFC Production Center
On Feb 13, 2026, at 9:52 AM, [email protected] wrote:
*****IMPORTANT*****
Updated 2026/02/13
RFC Author(s):
--------------
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--------------------------------------
RFC 9853 (draft-ietf-tls-dtls-rrc-20)
Title : Return Routability Check for DTLS 1.2 and DTLS 1.3
Author(s) : H. Tschofenig, Ed., A. Kraus, T. Fossati
WG Chair(s) : Joseph A. Salowey, Sean Turner, Deirdre Connolly
Area Director(s) : Deb Cooley, Paul Wouters
