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what are listeners?

Posted on 2004-05-01
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Last Modified: 2010-04-11
Hi there,

I hope if anyone help me on giving me a brief description about listeners in general..

or some webpages that will explain them for me,

thanks in advance,
waiting for ur answers :)
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Question by:SEstudent
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by:SEstudent
ID: 10966359
I must say that my question is about (port listeners)..
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Bing CISM / CISSP earned 43 total points
ID: 10966672
commonly, a listener is a program that is used to accept incoming connections, in order to provide specific services. it opens one or several listener sockets, each accepting TCP/IP connections on a specified port number, and, optionally on a specified local IP address.

hope it helps,
bbao
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Assisted Solution

by:rafael_acc
rafael_acc earned 41 total points
ID: 10967811
A listener is an Operating System Service wich waits for a connection on a predefined port, using a predefined protocol. Note that when using tcp/ip, different protocols may be used (because TCP/IP its a protocols stack) for example: ftp, smpt, http, ... etc. Each of these protocols use already defined fixed ports (known as well known ports). However there are services wich open ports in a dinamic fashion, only when needed.

If you type at your command prompt, "netstat -na <enter>" then you will better understant that. Trust me !

Cheers.
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by:fifthelement80
fifthelement80 earned 41 total points
ID: 10970269
u should know some basic knowledge of networking first let me explain u some basics :
1.in IP protocol every pc connected to network has an unique IP address and 65535 ports available to use.
2.every application uses some specific port number (it is software based not hardware) to let other clients or applications to communicate with it.
3.if an application listen on some port then that port is assumed as open.
4.1024 ports have common specific use like : 80 for WWW 21 for ftp 23 for telnet and ...
An Example :
your IP address is : 192.168.10.1
u have an webserver on your computer running then your webserver listens on port 80 and port 80 is open.
other computers connect through your computer through this address : http://192.168.10.1:80 (because of http 80 is not required)
and so they will be able to communicate to your application
Hope it helps

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