Port numbers.

If the ip address is considered the name of a city then its easy to understand the analogy for the term port. To send data on the internet you need both the ip address and the port number. By default all ports are open but you can only recieve data if you have programs listing on that port. Nearly all Internet services have there own default port number or port range(some use more than 1 port). This is put inside your software so you dont have to type the port in all the time. Here is a list of some simple ones.

HTTP(web) 80
ftp 21
telnet 23
SSH 22

Many server applications allow the changing of port numbers for security reasons so if you want to access something on another port you have to put a colon and then the port number after the address. Such as http://yahoo.com:2000. This of course does not work since no one would make an open website without using port 80 but many web services run by default on such ports such as cpanel.

Non standard applications such as games IM programs use there own ranges of defined ports. To find out what ports you are listing on you can go
start > run > command > netstat -n
or you can use a very good program called tcp view which allows you to view and kill you internet processes. It can be found here http://www.sysinternals.com/files/tcpview.zip

To find out what ports are not only open but also listning is a very good method of network reconnasance on your network(maybe hence the name). To this you use a thing called a port scanner. The one used in the matrix was a very popular standard text based scanner called NMAP but I would reccomend the use of the fast, very easy scanner SUPERSCAN..

If someone is listning on port 80 that means there most likely running a web server. If there listing on port 21 ftp ect. Using superscan you can scan for the ports based on an ip range you specify. This will give you there ip address and port number. So as so long as you have the password if there is any authentication and the ip addess and port number you can connect to there service using your preferred client(Firefox Putty CuteFTP etc.).
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