ECE - This flag is responsible for indicating if the TCP peer is ECN capable.RST - The reset flag gets sent from the receiver to the sender when a packet is sent to a particular host that was not expecting it.PSH - The push flag is somewhat similar to the URG flag and tells the receiver to process these packets as they are received instead of buffering them.The receiver will be notified when all known urgent data has been received. URG - The urgent flag is used to notify the receiver to process the urgent packets before processing all other packets.Therefore, it is used in the last packet sent from the sender. FIN - The finished flag means there is no more data from the sender.As we can see from the diagram above, the receiver sends an ACK as well as a SYN in the second step of the three way handshake process to tell the sender that it received its initial packet. ACK - The acknowledgment flag is used to acknowledge the successful receipt of a packet.The following diagram illustrates a three way handshake process. Only the first packet from both the sender and receiver should have this flag set. SYN - The synchronisation flag is used as a first step in establishing a three way handshake between two hosts.Additionally, check out the corresponding RFC section attributed to certain flags for a more comprehensive explanation. The list below describes each flag in greater detail.

List of TCP flagsĮach TCP flag corresponds to 1 bit in size. However, in this post, we're going to go through the full list of TCP flags and outline what each one is used for.

There are a few TCP flags that are much more commonly used than others as such SYN, ACK, and FIN. Therefore, they can be used for troubleshooting purposes or to control how a particular connection is handled. TCP flags are used within TCP packet transfers to indicate a particular connection state or provide additional information.

Using wireshark to recover flag