When an Initial packet is sent by a client that has not previously received an Initial or Retry packet from the server, the client populates the Destination Connection ID field with an unpredictable value. This Destination Connection ID MUST be at least 8 bytes in length. Until a packet is received from the server, the client MUST use the same Destination Connection ID value on all packets in this connection.
The Destination Connection ID field from the first Initial packet sent by a client is used to determine packet protection keys for Initial packets. These keys change after receiving a Retry packet; see Section 5.2.
RFC 9000 says:
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