Concept of Networking A to Z Epside-02

Concept of Networking A to Z Epside-02

How HTTP works?

 A Web browser usually opens to a starting or “home” page,

*where hyperlinks can be selected , or a URL in the address bar of the browser can be typed.

The Web browser examines the protocol, determines the IP address of the Web server using DNS.

*Then the transport layer, network layer, data link layer, and physical layer work together to initiate a session with the Web server.

*The data that is transferred to the HTTP server contains the folder name of the Web page location.

*The data can also contain a specific file name for an HTML page.

*If no name is given, then the default name as specified in the configuration on the server is used.

The server responds to the request

*send to the Web client all of the text, audio, video, and graphic files specified in the HTML instructions.

*The client browser reassembles all the files to create a view of the Web page, and then terminates the session.

                           #  SMTP
(Simple Mail Transfer Protocol)

Email servers communicate with the Simple Mail Transfer Protocol (SMTP) to send and receive mail.

*Email messages are transported in ASCII format using TCP.

*When a mail server receives a message destined for a local client,

*it stores that message and waits for the client to collect the mail.

*There are several ways for mail clients to collect their mail.

*Using programs that access the mail server files directly or collect their mail using network protocols, like POP3 and IMAP4.

*Mail clients use these special different protocols to collect mail, they almost always use SMTP to send mail.

#Two different protocols, and possibly two different servers, are used to send and receive mail,

*it is possible that mail clients can perform one task and not the other.

*Thus, usually troubleshooting is done separately for e-mail sending problems from e-mail receiving problems.


#SMTP connection

When checking the configuration of a mail client, a good way to verify that the SMTP and POP or IMAP settings are correctly configured, is-

*to test if a mail server is reachable is to Telnet to the SMTP port (25) or to the POP3 port (110).

*The following command format is used at the Windows command line to test the ability to reach the SMTP service on the mail server at IP address

C:\>telnet  25

The SMTP protocol does not offer much of security and does not require any authentication.

*Administrators often do not allow hosts that are not part of their network to use their SMTP server to send or relay mail.

*This is to prevent unauthorized users from using their servers as mail relays

#FTP (File Transfer Protocol)

*Connection-oriented service

*Uses TCP to transfer files between systems that support FTP.

*File is transferred by copying and moving files from servers to clients, and from clients to servers.

#How file copied from a server

1.FTP first establishes a control connection between the client and the server.

2.A second connection is established through which the data is transferred.

3.Data transfer can occur in ASCII mode or in binary mode.

4.After the file transfer, the data connection terminates automatically.

5.When the entire session of copying and moving files is complete, the command link is closed when the user logs off and ends the session.

How file copied from a server

#TFTP (Trivial File Transfer Protocol)

1.Connectionless service

2.Uses User Datagram Protocol (UDP).

3.Used on the router to transfer configuration files

4.TFTP is designed to be small and easy to implement. Therefore, it lacks most of the features of FTP. TFTP can read or write files to or from a remote server but it has no provisions for user authentication.

5.Useful in some LANs because it operates faster than FTP and in a stable environment it works reliably.

#SNMP (Simple Network Management Protocol )

1.(SNMP) is an application layer protocol

2.Facilitates the exchange of management information between network devices.

3.Enables network administrators to manage network performance, find and solve network problems, and plan for network growth.

4.SNMP uses UDP as its transport layer protocol.

#Components of SNMP managed network

Network management system (NMS)

*Executes applications that monitor and control managed devices

*One or more NMSs must exist on any managed network.

Managed devices

*Network nodes that contain an SNMP agent and that reside on a managed network.

*Collect and store management information and make this information available to NMSs using SNMP.

*Managed devices can be routers, access servers, switches, and bridges, hubs, computer    hosts.

#Components of SNMP managed network


*Network-management software modules that reside in managed devices.

*Has local knowledge of management information and translates that information into a form compatible with SNMP.

Components of SNMP managed network


*Telnet client software provides the ability to login to a remote Internet host that is running a Telnet server application and then to execute commands from the command line.

*A Telnet client is referred to as a local host.

*Telnet server, which uses special software called a daemon, is referred to as a remote host.

#Making a Telnet connection

*From a Telnet client, the connection option must be selected.

*A dialog box typically prompts for a host name and terminal type.

*The Telnet operation uses none of the processing power from the transmitting computer.

* All processing and storage take place on the remote computer.

Making a Telnet connection


*Telnet works at the application layer of the TCP/IP model.

*Telnet works at the top three layers of the OSI model.

*The application layer deals with commands.

*The presentation layer handles formatting, usually ASCII.

*The session layer transmits.

*In the TCP/IP model, all of these functions are considered to be part of the application layer.

Concept of Networking A to Z Epside-01


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