The client should then reply with an ACK indicating that it received the server SYN too.The server responds with a packet containing both an acknowledgement ( ACK) that it received the client's SYN and a SYN directed to the client.The client starts by sending a synchronization packet ( SYN) to the server it needs to connect to and waits for the server response.The TCP defines a 3-way handshake mechanism to initiate the connection. The following sequence diagram illustrates the 3-way handshake processĪnd this is how the handshake is captured by wiresharkĭuring this handshake, the client and the server also declare their capabilities for each other to agree on the common connection parameters to be used between them.
Also during the handshake, each side informs the other one what is its initial sequence number ( ISN).Įvery time a host sends a TCP packet, it will contain a sequence number which is the total number of sent bytes. The sequence number is not initialized with zero, it's initialized with a random number ISN for each side of the connection. The generic TCP parameters on each packet are: The expert view of Wireshark for each TCP packet will display packet parameters, flags and options. Stream index: This is not a real TCP parameter.Destination port: The port number of the side who should receive this packet.Source port: The port number of the side who transmitted this packet. It's only a Wireshark representation of the connection 4 values (source address, source port, destination address, and destination port). If one of these values changed, the sequence number will differ. TCP segment length: The size of the data contained on this packet.This can happen for example if you are capturing at the server-side and there is more than one client connected to the server, then each connection will have its sequence number.
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