11/14/2022 0 Comments Syn syn ack ack![]() If the connection is in a synchronized state (ESTABLISHED,įIN-WAIT-1, FIN-WAIT-2, CLOSE-WAIT, CLOSING, LAST-ACK, TIME-WAIT),Īny unacceptable segment (out of window sequence number or The connection remains in the same state. Of the sequence number and segment length of the incoming segment. Reset has sequence number zero and the ACK field is set to the sum Sequence number from the ACK field of the segment, otherwise the If the incoming segment has an ACK field, the reset takes its Match the local precedence level exactly, if it does not a reset Incoming segment) the precedence level of the incoming segment must If our SYN has been acknowledged (perhaps in this Incoming segment is lower than the precedence level requested thenĬontinue as if the precedence matched exactly (if the remote TCPĬannot raise the precedence level to match ours this will beĭetected in the next segment it sends, and the connection will be The system) or send a reset or if the precedence level of the Incoming segment is higher than the precedence level requested thenĮither raise the local precedence level (if allowed by the user and If our SYN has not been acknowledged and the precedence level of the If an incoming segment has a security level or compartment whichĭoes not exactly match the level and compartment requested for the Something not yet sent (the segment carries an unacceptable ACK), or SYN-SENT, SYN-RECEIVED), and the incoming segment acknowledges If the connection is in any non-synchronized state (LISTEN, The connection remains in the CLOSED state. Set to the sum of the sequence number and segment length of the Otherwise the reset has sequence number zero and the ACK field is Takes its sequence number from the ACK field of the segment, If the incoming segment has an ACK field, the reset Particular, SYNs addressed to a non-existent connection are rejectedīy this means. Response to any incoming segment except another reset. If the connection does not exist (CLOSED) then a reset is sent in A reset must not be sent if it is not clear that Whenever a segment arrives which apparently is not intended for theĬurrent connection. RFC 793, Transmission Control Protocol explains (I highlighted the relevant text):Īs a general rule, reset (RST) must be sent What number would it put into the field? It would be made up, so the receiving host would respond with a RST. That is not realistic because it does not have an acknowledgement number to acknowledge with the ACK flag. ![]()
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