What Are Ports?

What Are Ports?
Port is a term that is used often in networking. Regardless of whether your com-
puter is online or offline,your computer has a number of open channels to which
various programs or other computers can connect.These channels are known as
ports.Obviously,if your computer isn’t connected to a network,only the local pro-
gram will be able to access these ports.Once a computer is online,however,any-
one on the network can execute a client program on their remote computer to
connect to these ports.
Ports are channels created between two computers for the exchange of informa-
tion.A computer can have many open ports for receiving connection requests.For
example, a server that has HTTP, SMTP, POP, FTP, and Telnet services
can have five open ports.The default port numbers of HTTP,SMTP,POP,FTP,
and Telnet are 80,25,110,21,and 23,respectively.These ports are not hardware
components, but are like virtual stations within your computer’s memory.
All computers have them,including the server you dial to access the Internet.
When a computer is turned on, a number of ports are virtually created. These
remain open and search for programs that are running on remote or local com-
puters.This process is known as listening. If another computer wishes to connect
to a port on your computer, it can do this in two ways: by being offered a port
address to connect to,or by scanning available open ports.
Sometimes, your computer willingly gives a port number to another computer to
make a connection.At other times,the other computer might just guess or try one
of the universally known port numbers. However, hackers might also choose to
run a port scan through your computer from a remote location. A port scanner is
software that allows a user to search all ports that a server is listening to. When
such a program is used, the user simply has to type the IP address of the desired
computer, and the scanner presents a complete report of all ports that are being
NOTE
Port scanners are of two types: stealth and normal. Stealth port scanners are less
effective in finding open ports, but they can hide from intrusion detection systems,
firewalls, and an ISP’s administrative staff. Normal scanners, on the other hand, pro-
vide more information about open ports in a server and are used by administrators
because they do not need to hide within their own network.