we keep on listening this word Port Number this and that.. whenever we try to understand Networking there always comes the word Port /PORT Number. SO here we are going to discuss about what the port Number is ? . what is the use of port no in Networking.




so before we are going to  answer what the word port Number means . we have to understand the word "protocal " in computer Networking  so firstly  what is protocol ? ... protocol is simply standardized set of rules and regulation which determine how the data is transmitted between devices over the same networks..examples of protocols are as follows HTTPS , FTP ,SMTP , POP , IMAP ETC.. there are many more protocol which is used  for different different Purposes ..  for example As above FTP (File Transfer protocol ) is used for transmitting files between computers on the internet , SMTP ( simple Mail Transfer Protocol ) is used for  to send , receive  or relay out-coming / incoming mails between sender and receiver...so here we know the protocols by their name but our  system(os)  knows this protocols by assigning them logical address .  




we already Know  in our system their are thousand of  protocals ( application ) keep on running  so whenever we receive  anything from the internet ( network ) that packet contains this logical address (port no ). so when our system received it . at that time our system get to know about where to direct this packet on the system  by knowing this logical address . for example we received a mail from the internet so how our system get to know about this is a mail . so when we received this packet from the internet this packet contains port no which tells the system about where to directed this packet  and the protocal which is used for mail is SMTP  and the port no of this protocal is 25.so our packet contain this port number that is why our system get to know that this is a mail and reditected it towards the SMTP application.

Now lets try to understand this by an example. 




suppose a person send me a file without extension. that person only knows my ip address . so when i  received that file  my system unable recognise or run that file because that File does not contain any extension(  i.e mp3 , pdf , mp4 , txt ..etc). so in order to run this file we have add a suitable extension to that file Right . this what exactly happens in Networking whenever we received any packets from the internet that packet contains port no which tells the our system where to directed this packet in order to see it.