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

Errata ID: 6811
Status: Verified
Type: Technical
Publication Format(s) : TEXT, PDF, HTML
Reported By: Martin Thomson
Date Reported: 2022-01-06
Verifier Name: Zaheduzzaman Sarker
Date Verified: 2022-02-18

Section 5.1.1 says:

                                         The sequence number of the
   initial connection ID is 0.  If the preferred_address transport
   parameter is sent, the sequence number of the supplied connection ID
   is 1.

   Additional connection IDs are communicated to the peer using
   NEW_CONNECTION_ID frames (Section 19.15).  The sequence number on
   each newly issued connection ID MUST increase by 1.  

It should say:

                                         The sequence number of the
   initial connection ID is 0.  If the preferred_address transport
   parameter is sent, the sequence number of the supplied connection ID
   is 1.  The sequence number for NEW_CONNECTION_ID frames starts at 2
   when the preferred_address transport parameter is sent and 1
   otherwise.

   Additional connection IDs are communicated to the peer using
   NEW_CONNECTION_ID frames (Section 19.15).  The sequence number on
   each newly issued connection ID MUST increase by 1.

Notes:

It is not sufficiently clear that the (implied) sequence number for the preferred_address transport parameter is taken from the sequence only when the transport parameter is present.

The original text might be read to imply that the first NEW_CONNECTION_ID frame always starts with 2, though maybe only at a server. The proposed addition is much more explicit.

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