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Chapter 4: Transport And Application Layer 4.2 Explain Application Layer…

- - - - Session layer function:
        -create and maintain dialogs between source and destination applications.
  - - - Each device (known as a peer) can function as both a server and a client
  - - - also,P2P applications require that each end device provide a user interface and run a background service.
    - - Common P2P networks include:
        
        G2
        
        Bitcoin
        
        BitTorrent
        
        eDonkey
        
        Some P2P applications are based on the Gnutella protocol, where each user shares whole files with other users
        
        Many P2P applications allow users to share pieces of many files with each other at the same time –this is BitTorrent technology.
- - - - :fire:Nslookup-a utility that allows a user to manually query the name servers to resolve a given host
        . Can also be used to troubleshoot name resolution issues and to verify the current status of the name servers
  - - - :star: The Dynamic Host Configuration Protocol (DHCP) for IPv4 automates the assignment of IPv4 addresses, subnet masks gateway and other parameters
        :star: DHCP-distributed addresses are leased for a set period of time, then returned to pool for reuse
        
        :star: DHCP is usually employed for end user devices. Static addressing is used for network device such as gateways, switches, servers and printers
        :star: DHCPv6 (DHCP for IPv6) provides similar services for IPv6 clients
- - - - :check: Email is downloaded from the server to the client and then deleted on the server.
  - - - :check: Copies of messages are downloaded from the server to the client and the original messages are stored on the server.
  - - - :check: The SMTP protocol can only be used to send emails, not to receive them. Depending on your network / ISP settings, you may only be able to use the SMTP protocol under certain conditions
  - - - :check: Packet Tracer makes use of a drag and drop user interface, allowing users to add and remove simulated network devices as they see fit.
  - - - :check: Mail servers communicate with other mail servers to transport messages from one domain to another.
        
        :check: Three protocols for email:
        
        Simple Mail Transfer Protocol (SMTP) to send email.
        
        Post Office Protocol (POP) to retrieve email.
        
        Internet Message Access Protocol (IMAP) to retrieve email.
  - - - :point_right::skin-tone-3:The client establishes the first connection to the server for control traffic using TCP port 21.
      - :point_right::skin-tone-3:The client establishes the second connection to the server for the actual data transfer using TCP port 20.
  - - - HTTP Secure (HTTPS) protocol uses encryption and authentication to secure data
  - - - :pushpin:SMB file-sharing&print services have become the mainstay of Microsoft networking.
      - :pushpin:Client establish is a long-term connection to servers
        &
        can access the resources on the server as if the resource is local to the client host.