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 knowledge, basic and/or knowledge:
“Not many appreciate the ultimate power and potential usefulness of basic knowledge accumulated by obscure, unseen investigators who, in a lifetime of intensive study, may never see any practical use for their findings but who go on seeking answers to the unknown without thought of financial or practical gain.”
—Eugenie Clark (b. 1922)
“Nothing and no one can destroy the Chinese people. They are relentless survivors. They are the oldest civilized people on earth. Their civilization passes through phases but its basic characteristics remain the same. They yield, they bend to the wind, but they never break.”
—Pearl S. Buck (1892–1973)
“A belief in hell and the knowledge that every ambition is doomed to frustration at the hands of a skeleton have never prevented the majority of human beings from behaving as though death were no more than an unfounded rumour.”
—Aldous Huxley (1894–1963)