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Topic 5: Transport and Application Layer, Steps DNS resolves domain names…

- - - - Set Up Your Topology
      - Create a basic topology with:
      - 1 Server
      - 1 Switch
      - 1 Router (optional, if using different networks)
      - 2+ PCs or Laptops
  - - - Configure the Server (DHCP + DNS)
      - Click on the Server → Go to Config tab.
      - FastEthernet0:
      - IP Address: 192.168.1.10
      - Subnet Mask: 255.255.255.0
      - Default Gateway: 192.168.1.1
  - - - DHCP Configuration
      - Go to DHCP on the left menu (inside the Server).
      - Click On to enable it.
      - Fill out the fields:
      - Pool Name: LAN
      - Default Gateway: 192.168.1.1
      - DNS Server: 192.168.1.10 (same as this server)
      - Start IP Address: 192.168.1.100
      - Subnet Mask: 255.255.255.0
      - Maximum Users: 50
      - Click Add.
  - - - DNS Configuration
      - Go to Services tab → Click on DNS.
      - Turn the service On.
      - Add a domain:
      - Name: www.example.com
      - Address: 192.168.1.20 (you can point it to another PC for testing)
      - Click Add.
  - - - Configure the PCs
      - Click on each PC → Go to Config → FastEthernet0.
      - Select DHCP to get settings from the server.
      - After a few seconds, you should see:
      - IP Address: 192.168.1.x
      - Subnet Mask: 255.255.255.0
      - Default Gateway: 192.168.1.1
      - DNS Server: 192.168.1.10
  - - - Test DNS
      - On a PC, go to Desktop → Web Browser.
      - Type www.example.com → It should resolve and open the IP address you configured.
      - Or use Command Prompt → ping www.example.com
- - - - HTTPS (HTTP Secure)
      - A secure version of HTTP.
      - Data is encrypted using SSL/TLS.
      - Protects user privacy and security.
      - Uses port 443.
      - URL starts with https://.
  - - - SMTP (Simple Mail Transfer Protocol)
      - Send email.
      - Does not store email on server.
      - Used when pressing the "Send" button.
      - POP3 (Post Office Protocol version 3)
        
        Used to receive emails.
        
        Emails are downloaded to the device and usually deleted from the server.
        
        Best for one-device access.
      - IMAP (Internet Message Access Protocol)
        
        Also used to receive emails.
        
        Emails are kept on the server and can be accessed from multiple devices.
        
        All changes (read, delete, move) are synchronized.
      - Main difference:
        
        SMTP = Sending emails
        
        POP3 = Receiving emails (stored on device)
        
        IMAP = Receiving emails (stored on server, synced across devices)
- - - - Features =>
        
        HTTP (Port 80): Loads websites (text, images) in plain text.
        
        HTTPS (Port 443): Same as HTTP but encrypted (🔒 secure for passwords, payments).
      - Advantages =>
        
        Easy: Works in every browser (Chrome, Firefox).
        
        Safe (HTTPS): Stops hackers from snooping.
      - Disadvantages =>
        
        HTTP is risky: Like sending a postcard—anyone can read it.
        
        HTTPS Setup: Needs a security certificate (free options exist).
    - - Features =>
        
        Transfers files between computers on a network (like downloading/uploading files from a server).
      - Advantages =>
        
        Efficient for large files: FTP can transfer large files quickly and is reliable for transferring multiple files at once.
        
        Multiple modes: It can work in active or passive mode, depending on network configurations.
      - Disadvantages =>
        
        Security risk (FTP vs. FTPS): Standard FTP transfers data in plain text, so credentials and files can be intercepted by hackers.
        
        Needs configuration: You need to set up the FTP server and manage user permissions to ensure safety.
  - - - Features =>
        
        Real-time voice communication over the internet.
        
        Requires consistent, low-latency delivery rather than perfect accuracy.
      - Advantages =>
        
        Low latency: Enables natural, real-time conversation.
        
        Faster transmission: No delay from handshakes or retransmission like TCP
      - Disadvantages =>
        
        Packet loss affects call quality: You might hear gaps, glitches, or robotic voices.
        
        No built-in security: Calls can be intercepted or spoofed
    - - Features =>
        
        Real-time transmission of video/audio.
        
        Uses buffering to smooth out brief network issues.
      - Advantages =>
        
        Low latency: Ideal for real-time performance (no delay).
        
        Supports multicast: One sender can stream to many receivers
      - Disadvantages =>
        
        Packet loss affects video quality: Lost packets mean skipped frames or frozen video. No retransmission.
        
        No flow control: UDP doesn't slow down if network is congested, which can overwhelm the receiver.
- - - - Connection type – connectionless
      - Reliability – unreliable (no delivery guarantee or order)
      - Ordering – no order guarantee
      - Speed – faster due to minimal overhead
      - Header Size – smaller (8 bytes)
      - Data Transmission – datagram/message-based
      - Use Cases – streaming (audio/video), VoIP, online gaming
    - - Connection type – connection-oriented
      - Reliability – guarantees delivery, order and error checking
      - Ordering – ensures packet order
      - Speed – slower due to overhead of reliability features
      - Header Size – larger (20-60 bytes)
      - Data Transmission – Stream-based
      - Use Cases – web (http/https), email (smtp), file transfer (ftp)
- - - - SYN - ACK (synchronization acknowledge)
        • Server responds to client’s SYN packet with a SYN/ACK packet
        .
        Sets SYN and ACK flags:
        • ACK: Acknowledges client’s sequence number.
        • SYN: Sends server’s own sequence number.
        •Confirms the client’s connection request.
        •Shares the server’s initial sequence number with the client
        .