Flag options in TCP

When using Network monitor to analyze Network communication packets, such knowledge points as TCP Flag are often used.

 

 

So what are the meanings of these flags?

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Urgent flagIs used to identify incoming data as 'urgent'. Such incoming segments do not have to wait until the previous segments are consumed by the processing end but are sent directly and processed immediately.

 

ACKnowledgement flagIs used to acknowledge the successful receipt of packets.

 

Reset flagIs used when a segment arrives that is not intended for the current connection. in other words, if you were to send a packet to a host in order to establish a connection, and there was no such service waiting to answer at the remote host, then the host wowould automatically reject your request and then send you a reply with the RST flag set. this indicates that the remote host has reset the connection.

 

SYN flagIs initialy sent when establishing the classical 3-way handshake between two hosts.

 

FIN flag, Standing for the word FINished. this flag is used to tear down the virtual connections created using the previous flag (SYN), so because of this reason, the FIN flag always appears when the last packets are exchanged between a connection.

 

TCP three-way handshake to establish a connection

 

TCP disconnection, Process

 

Source:

TCP Analysis-Section 4: TCP Flag Options

Http://www.firewall.cx/tcp-analysis-section-4.php