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

4.2.1 Explain how the functions of the application layer, session layer, and presentation layer work together to provide network services to end user applications.

4.2.3 Explain how DNS and DHCP operate

4.2.2 Explain how web and email protocols operate.

GUIDE

AINOR

KHAIRI

DAYANGKU UMI AFFIFAH

SCARLETT DYER SYED

GRACELINA KUMBAU

5. POP Operation

6. IMAP Operation

4. SMTP Operation

7. Packet Tracer – Web and Email

3. Email Protocols

  1. File Transfer Protocol
  1. HTTP and HTTPS
  1. Server Message Block
  1. Hypertext Transfer Protocol and Hypertext Markup Language

4.Client-server Model

2.presentation and session layer

  1. Peer-to-Peer Networks/Peer-to-Peer Applications

3.TCP/IP Application layer protocols

  1. Peer-to-Peer Applications

1. Application Layer

  1. DNS Hierarchy
  1. The nslookup Command
  1. DNS Message Format

5. Dynamic Host Configuration Protocol

  1. Domain Name Service

6. DHCP Operation

✅ Email clients communicate with mail servers to send and receive email.

✅ Mail servers communicate with other mail servers to transport messages from one domain to another.

✅ 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.

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✅ The SMTP (Simple Mail Transfer Protocol) protocol is used by the Mail Transfer Agent (MTA) to deliver your eMail to the recipient's mail server.

✅ 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

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✅ POP is used to retrieve email from a mail server.

✅ Email is downloaded from the server to the client and then deleted on the server.

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✅ IMAP is used to retrieve mail from a mail server

✅ Copies of messages are downloaded from the server to the client and the original messages are stored on the server.

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✅ cross-platform visual simulation tool designed by Cisco Systems that allows users to create network topologies and imitate modern computer networks.

-Closest to the end user


-used to exchange data between programs running on the source and destination hosts.

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presentation layer function:
-formatting data at the source device into a compatible form for the receiving device.
-compressing data
-encrypting data

Session layer function:
-create and maintain dialogs between source and destination applications.

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-domain name server (DNS) TCP,UDP 53- translate domain names such as cisco.com, into IP addresses.


-(BOOTP) -Bootstrap Protocol- BOOTP is being superseded by DHCP


-Dynamic host configuration Protocol (DHCP) UDP client 68,server 67-dynamically assigns IP addresses to client stations at start-up


-simple mail transport protocol (SMTP) TCP 25-enable client to send email to a mail server.


-Post Office Protocol (POP) TCP 110 -Enables clients to retrieve email from a mail server.


-internet message acces protocol (IMAP) TCP143- enable clients to retrieve email from a mail server,maintain email on server.


-file transfer protocol (FTP)TCP20 and 21-reliable,connection-oriented and acknowledged file delivery protocol.


-trivial file transfer protocol (TFTP) UDP 69- simple connectionless file transfer protocol.


-hypertest transfer protocol (HTTP) TCP 80,8080-set of rules for exhanging test,graphic images etc on the world wide web.


-hypertext transfer protocol secure (HTTPS) TCP.UDP 443-use encryption and authentication to secure communication.

👉🏼 FTP requires 2 connections between the client & the server , one for commands & replies , the other for the actual file transfer.

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👉🏼The client establishes the first connection to the server for control traffic using TCP port 21.

Data is accessed from a peer device without the use of a dedicated server

-client and server processes are considered to be in the application layer


-application layer protocols describe the format of the requests and responses between clients and servers.


-example of a client-server network is using an ISP's email service to send,receive and store email

👉🏼The client establishes the second connection to the server for the actual data transfer using TCP port 20.

Each device (known as a peer) can function as both a server and a client

📌SMB is a client/server file sharing protocol.

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📌SMB file-sharing&print services have become the mainstay of Microsoft networking.

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📌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.

💡Domain names convert the numeric address into a simple, recognizable name.

👩🏻‍🏫When a client makes a query, the server's DNS process first looks at its own records to resolve the name.

💡DNS protocol defines an automated service that matches resource names with the required numeric network address.

👩🏻‍🏫If unable to resolve, it contacts other servers to resolve the name.

👩🏻‍🏫The server temporarily stores the numbered address in the event that the same name is requested again.

👩🏻‍🏫The ipconfig/displaydns command displays all of the cached DNS entries on a Windows PC.

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💥 DNS uses a hierarchy to managed its distributed database system and also called the domain name space, is an inverted tree structure much like eDirectory

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🔥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

A P2P application allows a device to act as both a client and a server within the same communication

also,P2P applications require that each end device provide a user interface and run a background service.

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When a web address or uniform resource locator (URL) is typed into a web browser, the web browser establishes a connection to the web service running on the server, using the HTTP protocol

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⭐ The Dynamic Host Configuration Protocol (DHCP) for IPv4 automates the assignment of IPv4 addresses, subnet masks gateway and other parameters
⭐ DHCP-distributed addresses are leased for a set period of time, then returned to pool for reuse

Common P2P Applications

Common P2P networks include:

  • G2
  • Bitcoin
  • BitTorrent
  • eDonkey

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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.

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⭐ DHCP is usually employed for end user devices. Static addressing is used for network device such as gateways, switches, servers and printers
⭐ DHCPv6 (DHCP for IPv6) provides similar services for IPv6 clients

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HTTP is a request/response protocol. Three common HTTP message types are:

  • GET - A client request for data.
  • POST - Uploads data files to the web server.
  • PUT - Uploads resources or content to the web server

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HTTP Secure (HTTPS) protocol uses encryption and authentication to secure data

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🎉 DHCP(Dynamic Host Configuration Protocol) works in a client/ server mode.
🎉 DHCP enables clients on an IP network to obtain or lease IP address or configuration form a DHCP server

✅ Packet Tracer makes use of a drag and drop user interface, allowing users to add and remove simulated network devices as they see fit.

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