TCP/IP Flags

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TCP, the Transmission Control Protocol, uses flags to control the flow of data between devices on a network. These flags are included in the header of each TCP segment, and are used to indicate the status of the connection and the type of data being transmitted. The following are the commonly used TCP flags:

  • SYN (Synchronize): Used to initiate a new TCP connection. It is the first step in the three-way handshake process.

  • ACK (Acknowledgment): Indicates that the receiving device has received the data and is acknowledging receipt.

  • FIN (Finish): Indicates that the sender has finished sending data and is closing the connection.

  • RST (Reset): Indicates that the connection is being reset. This can occur if there is an error or if the receiving device is unable to process the data.

  • PSH (Push): Indicates that the data should be pushed to the receiving device immediately, rather than being buffered.

  • URG (Urgent): Indicates that the data being sent is urgent and should be processed immediately.

  • ECE (ECN-Echo) & CWR (Congestion Window Reduced): used to indicate congestion control on the network.

These flags are used in combination with each other to control the flow of data and ensure reliable communication between devices on a network.

The Transmission Control Protocol (TCP) uses flags in the header of each segment to control the flow of data between devices on a network. These flags are used to indicate the status of the connection and the type of data being transmitted.

  • SYN (Synchronize): This flag is used to initiate a new TCP connection. It is the first step in the three-way handshake process. A device sends a SYN flag to another device to initiate a connection, and the receiving device responds with an SYN-ACK flag to confirm that it is ready to establish a connection. Once the initiating device receives the SYN-ACK flag, it sends an ACK flag to complete the three-way handshake process and establish a connection.

  • ACK (Acknowledgment): This flag is used to indicate that the receiving device has received data and is acknowledging receipt. It is set in all segments after the initial SYN segment during the three-way handshake process.

  • FIN (Finish): This flag is used to indicate that the sender has finished sending data and is closing the connection. The receiving device must respond with an ACK flag to confirm that it has received the FIN flag and that the connection can be closed.

  • RST (Reset): This flag is used to indicate that the connection is being reset. This can occur if there is an error or if the receiving device is unable to process the data. A device receiving a RST flag must immediately terminate the connection.

  • PSH (Push): This flag is used to indicate that the data should be pushed to the receiving device immediately, rather than being buffered. This flag is used to ensure that data is delivered to the application as soon as possible.

  • URG (Urgent): This flag is used to indicate that the data being sent is urgent and should be processed immediately. This is used for real-time applications, such as voice and video.

  • ECE (ECN-Echo) & CWR (Congestion Window Reduced): These flags are used to indicate congestion control on the network. ECE indicates that the sender is using Explicit Congestion Notification (ECN) to signal network congestion and CWR indicate that the sender is reducing its congestion window.

In summary, TCP flags are used to control the flow of data and ensure reliable communication between devices on a network. They are used in combination with each other to establish connections, acknowledge receipt of data, close connections, reset connections, push data, and signal urgent data or congestion.


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