Trivia – TCP/IP Common Flags

TCP (Transmission Control Protocol) is a connection oriented protocol. Connection oriented protocol means that it ensure reliable or guaranteed communication. Before transmitting any data, it will first exchange messages to ensure that the connection is established. 

Meanwhile, different from TCP, UDP (User Datagram Protocol) is a connectionless protocol. It is simple and has lower bandwidth overhead than TCP, but it does not guarantee the delivery of the data.

In the TCP header, there are flags (control bits) that indicate a particular state of the connection or other additional information. There are many flags used in TCP, and these 6 flags are the most common ones:

Flag	Description
SYN (Synchronize)	Used in the first step of connection establishment for synchronizing sequence number to tell the target which sequence number they should accept.
ACK (Acknowledgement)	Used to acknowledge successful packet transmission.
FIN (Finish)	Used to request to terminate connection (it is the last packet sent by sender).
RST (Reset)	Used to terminate connection if the RST sender feels something wrong with the connection.
URG (Urgent)	Used to indicate that the data should be prioritized and handled urgently by the receiver.
PSH (Push)	Used to request immediately data to be sent immediately without waiting for the additional data to be buffered.

TCP ensures guaranteed delivery by conducting a three-way handshake to establish a connection first.

1.     Client to Server: SYN flag for connection request.

2.     Server to Client: SYN-ACK flags to acknowledge the request.

3.     Client to Server: ACK flag to indicate that the connection has been established.

 

And that’s all for our trivia. See you!

 

References:

https://www.geeksforgeeks.org/tcp-flags/

Chapple, M., & Zacker, C. (2021). CompTIA Network+ Certification Kit: Exam N10-008. Sybex.