![]() ![]() Indicates that the segment portion of the TCP segment contains urgent data and the Urgent Pointer field should be used to determine the location of the urgent data in the segment. URG (Urgent Pointer field is significant).URG and PSH are used during data transfer. TCP Flags For Normal Data Transfer Connection The exchange of these flags is performed in three steps: SYN, SYN-ACK, ACK. The connection is full-duplex, and both sides synchronize (SYN) and acknowledge (ACK) each other. TCP uses a three-way handshake to establish a reliable connection. The ACK flag is always set, except for the first segment of a TCP connection establishment. This indicates that the Acknowledgment field contains the next byte expected on the connection. ACK (Acknowledgment field is significant).The Acknowledgment Number field for the acknowledgment of the SYN segment is set to ISN + 1. Each TCP peer acknowledges the receipt of the SYN flag by treating the SYN flag as if it were a single byte of data. During the TCP connection establishment process, TCP sends a TCP segment with the SYN flag set. This indicates that the segment contains an ISN. SYN and ACK TCP flags are used for TCP 3 way handshake to establish connections. We can use tcpdump to filter packets with TCP flags. TCP flags can be combined together to make TCP data transfer efficiently like ack-psh in one TCP segment. ![]() Here are the numbers which match with the corresponding TCP flags.
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