RFC Errata
RFC 9000, "QUIC: A UDP-Based Multiplexed and Secure Transport", May 2021
Source of RFC: quic (tsv)
Errata ID: 7578
Status: Reported
Type: Technical
Publication Format(s) : TEXT, PDF, HTML
Reported By: Marten Seemann
Date Reported: 2023-07-30
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.