TCP/IP Basic Knowledge
The design and operation of the Internet is based on the Internet Protocol Suite, commonly also called TCP/IP. In this system, hosts and host services are referenced using two components: an address and a port number. There are 65536 distinct and usable port numbers. Most services use a limited range of numbers.
Some port scanners scan only the most common port numbers, or ports most commonly associated with vulnerable services, on a given host. See: List of TCP and UDP port numbers.
The result of a scan on a port is usually generalized into one of three categories:
- Open or Accepted: The host sent a reply indicating that a service is listening on the port.
- Closed or Denied or Not Listening: The host sent a reply indicating that connections will be denied to the port.
- Filtered, Dropped or Blocked: There was no reply from the host.
Open ports present two vulnerabilities of which administrators must be wary:
- Security and stability concerns associated with the program responsible for delivering the service - Open ports.
- Security and stability concerns associated with the operating system that is running on the host - Open or Closed ports.
Filtered ports do not tend to present vulnerabilities.
Read more about this topic: Port Scanner
Famous quotes containing the words basic and/or knowledge:
“The basic difference between classical music and jazz is that in the former the music is always greater than its performance—Beethoven’s Violin Concerto, for instance, is always greater than its performance—whereas the way jazz is performed is always more important than what is being performed.”
—André Previn (b. 1929)
“At no time in history ... have the people who are not fit for society had such a glorious opportunity to pretend that society is not fit for them. Knowledge of the slums is at present a passport to society—so much the parlor philanthropists have achieved—and all they have to do is to prove that they know their subject. It is an odd qualification to have pitched on; but gentlemen and ladies are always credulous, especially if you tell them that they are not doing their duty.”
—Katharine Fullerton Gerould (1879–1944)