3.1.5.1.2 CONNECTED
If the bExtOpcode field indicates FRAME_EXOPCODE_CONNECTED (0x02), the source address (for example, IPv4 address and port type when running on UDP) for the message SHOULD be checked. If the address does not correspond to one with an existing partially or fully established connection, it SHOULD be ignored.
If the source address matches that of a previously initiated outbound connection that has not completed the handshake process, the dwSessID field MUST match that of the previously sent CONNECT packet, and the PACKET_COMMAND_POLL flag MUST be set in the bCommand field before the packet can be accepted. If the connector is enforcing signing, this unsigned response SHOULD be ignored. Otherwise, the connection is considered to be established and a CONNECTED response sent to confirm this connection.
If the source address matches that of a previously initiated inbound connection that has not completed the handshake process, the dwSessID field MUST match that of the previously received CONNECT, and the PACKET_COMMAND_POLL flag MUST NOT be set in the bCommand field before the packet can be accepted. If the connector is enforcing signing, this unsigned response SHOULD be ignored. Otherwise, the connection SHOULD be considered established.
If the source address matches that of an established connection, the dwSessID field MUST match the one used to establish the connection, and the PACKET_COMMAND_POLL flag MUST be set. If so, this connector's previous CONNECTED response was apparently lost and the connector SHOULD send a duplicate CONNECTED packet. Otherwise, the packet SHOULD be ignored.