LinuxDynasty

TCP

Create a connection

It uses a three-way handshake

1. The
   client [a machine/device requesting a service/connection] sends a SYN flag
   & the server port number of the service it wants to communicate (i.e.
   Port 80 for http/web services)
   The packet also includes the client’s Initial Sequence Number (ISN)
2. Server
   – Resplies with it’s own SYN flag & ISN to the client’s TCP port
   An ACK flag is included in the packet in reply to the client’s SYN flag
3. Client
   replies with an ACK flag that acknowledges the server’s SYN Flag
   

Terminate a
connection

After all data is sent or session no longer needs the
session is terminated. This can be done either by client or server. Here is an
example of what is called an active
close

1. The
   application (i.e. Web browser –Firefore) on the client sends a close command to the application
   (i.e. Web Server – Apache) on the
   server
2. Server
   sends a FIN flag to client
3. Client
   sends an ACK flag to acknowledge the FIN flag
4. Client
   sends a FIN flag to server
5. Server
   replies with ACK flag –acknowledging the termination of the TCP connection

Flags used in TCP
Connections?

SYN Synchronized sequence number
FIN Sender FINished sending data –end connection
RST Reset Connection
PSH Push the data
ACK Acknowledgment
URG Urgent