Code change:
5.8.2. <del> Though timer values are the choice of the implementation, mishandling of the timer can lead to serious congestion problems, for example if many instances of a DTLS time out early and retransmit too quickly on a congested link.  Implementations SHOULD use an initial timer value of 100 msec (the minimum defined in RFC 6298 RFC6298) and double the value at each retransmission, up to no less than 60 seconds (the RFC 6298 maximum).  Application specific profiles, such as those used for the Internet of Things environment, may recommend longer timer values.  Note that a 100 msec timer is recommended rather than the 3-second RFC 6298 default in order to improve latency for time- sensitive applications.  Because DTLS only uses retransmission for handshake and not dataflow, the effect on congestion should be minimal. </del> <ins> The configuration of timer settings varies with implementations and certain deployment environments require timer value adjustments. Mishandling of the timer can lead to serious congestion problems, for example if many instances of a DTLS time out early and retransmit too quickly on a congested link.  Implementations SHOULD use an initial timer value of 100 msec (the minimum defined in RFC 6298 RFC6298) and double the value at each retransmission, up to no less than 60 seconds (the RFC 6298 maximum).  Application specific profiles, such as those used for the Internet of Things environment, may recommend longer timer values.  Note that a 100 msec timer is recommended rather than the 3-second RFC 6298 default in order to improve latency for time-sensitive applications.  Because DTLS only uses retransmission for handshake and not dataflow, the effect on congestion should be minimal. </ins> Implementations SHOULD retain the current timer value until a message is transmitted and acknowledged without having to be retransmitted,

Related discussion:
text: This document has been reviewed as part of the transport area review team's ongoing effort to review key IETF documents. These comments were written primarily for the transport area directors, but are copied to the document's authors and WG to allow them to address any issues raised and also to the IETF discussion list for information. When done at the time of IETF Last Call, the authors should consider this review as part of the last-call comments they receive. Please always CC EMAIL if you reply to or forward this review. TSV-ART Review of draft-ietf-tls-dtls13-41 Reviewer: Bernard Aboba Summary: The timeout and retransmission scheme looks workable for common cases, but could use some refinement to make it more robust. Technical Comments Handling Invalid Records Unlike TLS, DTLS is resilient in the face of invalid records (e.g., invalid formatting, length, MAC, etc.). In general, invalid records SHOULD be silently discarded, thus preserving the association; however, an error MAY be logged for diagnostic purposes. [BA] How does silent discard of invalid records interact with retransmission timers? Implementations which choose to generate an alert instead, MUST generate error alerts to avoid attacks where the attacker repeatedly probes the implementation to see how it responds to various types of error. Note that if DTLS is run over UDP, then any implementation which does this will be extremely susceptible to denial-of-service (DoS) attacks because UDP forgery is so easy. Thus, this practice is NOT RECOMMENDED for such transports, both to increase the reliability of DTLS service and to avoid the risk of spoofing attacks sending traffic to unrelated third parties. [BA] "this practice" refers to "generate an alert instead", correct? Timer Values Though timer values are the choice of the implementation, mishandling of the timer can lead to serious congestion problems, for example if [BA] Saying "timer values are the choice of the implementation" seems odd, because it is followed by normative language. I would delete this and start the sentence with "Mishandling...". many instances of a DTLS time out early and retransmit too quickly on a congested link.