RFC 9000, "QUIC: A UDP-Based Multiplexed and Secure Transport", May 2021

Errata ID: 7578
Status: Held for Document Update
Type: Technical
Publication Format(s) : TEXT, PDF, HTML
Reported By: Marten Seemann
Date Reported: 2023-07-30
Held for Document Update by: Zaheduzzaman Sarker
Date Held: 2024-01-29

Section 17.2.1 says:

                                                       Where QUIC
   might be multiplexed with other protocols (see [RFC7983]), servers
   SHOULD set the most significant bit of this field (0x40) to 1 so that
   Version Negotiation packets appear to have the Fixed Bit field.

It should say:

                                                       Unless the
   server has out-of-band knowledge that clients are not
   demultiplexing QUIC with other protocols (see [RFC7983]), it
   SHOULD set the most significant bit of this field (0x40) to 1 so that
   Version Negotiation packets appear to have the Fixed Bit field.

Notes:

Unless operating in a tightly controlled environment, the server has no way of knowing what other protocols the client might be demultiplexing on the same UDP socket. According to the demultiplexing logic defined in RFC 9443, Version Negotiation packets with 0x40 set to 0 would be misclassified as RTP/RTCP.

Looking at the discussion in https://mailarchive.ietf.org/arch/msg/quic/oR4kxGKY6mjtPC1CZegY1ED4beg/ and IETF118 QUIC working group meeting minutes. This needs more discussion to reach a conclusion on the potential solution.

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