Knowing Networks - Fundamentals

Knowing Networks - Fundamentals

1. OSI - 7 Layers

   • 7 - Application
     • 6 - Presentation
       • 5 - Session
         • 4 - Transport
           • 3 - Network
             • 2 - Data-Link
               • 1 - Physical

2. TCP/IP Model

   • Application
     • Transport
       • Internet
         • Network

3. THREE WAY HANDSHAKE TCP - Originating client sends out a packet with a SYN Flag and a Seq Number (X). The server replies with a SYN/ACK and own Seq Number (Y) and an acknowledgement of the client no X + 1. The Client will reply an ACK and increments its own seq number (X+1) and the sequence number of the server (Y+1). Connection created client can now start transmitting the data to the server. Connection remains until Client or Server sends a FIN packet or an RST packet to reset the connection / connection times out.

4. Well Know Ports: FTP: 20-21, SSH 22, Telnet 23, DNS 53, SMTP 25, HTTP 80, HTTPS 443