target = "https://www.rfc-editor.org/rfc/rfc9000#section-17.2.1"

# 17.2.1.  Version Negotiation Packet
#
# A Version Negotiation packet is inherently not version specific.
# Upon receipt by a client, it will be identified as a Version
# Negotiation packet based on the Version field having a value of 0.
# 
# The Version Negotiation packet is a response to a client packet that
# contains a version that is not supported by the server.  It is only
# sent by servers.
# 
# The layout of a Version Negotiation packet is:
# 
# Version Negotiation Packet {
#   Header Form (1) = 1,
#   Unused (7),
#   Version (32) = 0,
#   Destination Connection ID Length (8),
#   Destination Connection ID (0..2040),
#   Source Connection ID Length (8),
#   Source Connection ID (0..2040),
#   Supported Version (32) ...,
# }
# 
#                 Figure 14: Version Negotiation Packet
# 
# The value in the Unused field is set to an arbitrary value by the
# server.  Clients MUST ignore the value of this field.  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.  Note
# that other versions of QUIC might not make a similar recommendation.
# 
# The Version field of a Version Negotiation packet MUST be set to
# 0x00000000.
# 
# The server MUST include the value from the Source Connection ID field
# of the packet it receives in the Destination Connection ID field.
# The value for Source Connection ID MUST be copied from the
# Destination Connection ID of the received packet, which is initially
# randomly selected by a client.  Echoing both connection IDs gives
# clients some assurance that the server received the packet and that
# the Version Negotiation packet was not generated by an entity that
# did not observe the Initial packet.
# 
# Future versions of QUIC could have different requirements for the
# lengths of connection IDs.  In particular, connection IDs might have
# a smaller minimum length or a greater maximum length.  Version-
# specific rules for the connection ID therefore MUST NOT influence a
# decision about whether to send a Version Negotiation packet.
# 
# The remainder of the Version Negotiation packet is a list of 32-bit
# versions that the server supports.
# 
# A Version Negotiation packet is not acknowledged.  It is only sent in
# response to a packet that indicates an unsupported version; see
# Section 5.2.2.
# 
# The Version Negotiation packet does not include the Packet Number and
# Length fields present in other packets that use the long header form.
# Consequently, a Version Negotiation packet consumes an entire UDP
# datagram.
# 
# A server MUST NOT send more than one Version Negotiation packet in
# response to a single UDP datagram.
# 
# See Section 6 for a description of the version negotiation process.

[[spec]]
level = "MUST"
quote = '''
Clients MUST ignore the value of this field.
'''

[[spec]]
level = "SHOULD"
quote = '''
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.
'''

[[spec]]
level = "MUST"
quote = '''
The Version field of a Version Negotiation packet MUST be set to
0x00000000.
'''

[[spec]]
level = "MUST"
quote = '''
The server MUST include the value from the Source Connection ID field
of the packet it receives in the Destination Connection ID field.
'''

[[spec]]
level = "MUST"
quote = '''
The value for Source Connection ID MUST be copied from the
Destination Connection ID of the received packet, which is initially
randomly selected by a client.
'''

[[spec]]
level = "MUST"
quote = '''
Version-
specific rules for the connection ID therefore MUST NOT influence a
decision about whether to send a Version Negotiation packet.
'''

[[spec]]
level = "MUST"
quote = '''
A server MUST NOT send more than one Version Negotiation packet in
response to a single UDP datagram.
'''