Ports in FTP or other linked computer connections

Question

What are the ‘ports’ in FTP or other linked computer connections representing/how do they work? What is their purpose and how do you determine which port number you need?

In: Technology

Answer 1

They’re a way of differentiating traffic to different applications.

So, the bytes of data coming out of the ethernet adapter/device are read by the device driver and then a low level networking protocol that does only one thing very well and very fast: it receives and buffers incoming and outgoing network traffic. Its like the mailroom in a big office building or the shipping/receiving department of a factory. It doesn’t care what comes in or why, it just deals with the delivery drivers and such and finds a spot to put the stuff. Then higher level protocols will look at where it came from and what port (department in our analogy) its destined to. These higher level protocols will slot the incoming packets into special buffers or bins or spools or memory addresses that will be read by each specific program. Like this mail is for “finance” or “accounts payable” or “engineering”. Then, those specific programs get sent a signal or some kind of communication saying “you’ve got mail!” and then those programs can read the incoming stuff at their leisure. Or not.

So lets say an incoming game packet comes in. The network protocols shove the packets addressed to that port into some reserved memory or storage and flags the game that it has new packets, then the networking code in the game comes and gets it. Actually in the case of game networking its more like the game department sent one of their interns to go hang out in the mail room and they grab the message for the game as soon as it arrives and takes up to Game Department immediately and comes back to wait for the next one. But lets say email. Outlook will say “just dump incoming mail into this file over here network stack and I’lkl check it every 10 minutes.

So your computers IP address is like a building street address, ports are like the specific mailbox or department or even person (some programs can “listen” on multiple ports) within that building.