Welcome to tcpipworld.com Blog Post # 6
It is our attitude at the beginning of a difficult task which, more than anything else, will affect its successful outcome.- William James
In this, we will discuss TCP Flags “SYN” & “ACK”
1. SYN Flag
The SYN Flag synchronizes sequence number to initiate a TCP connection.
On the other hand FIN flag is just like the SYN Flag it occupies 1 byte in the sequence number space.
The advertise window appears to be 1 byte smaller because TCP allows room for the 1 byte of sequence number space occupied by the FIN Flag.
We will deep-dive into this during our connection establishment and connection termination blog.
2. ACK Flag
Sending an ACK costs nothing because the 32 bit Acknowledgment number field is always part of the TCP header.
Therefore we will see that once the connection established, this field is always set.
Let see in the packet capture, every TCP data has an ACK number associated with the ACK flag.