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associated with well-known port numbers.
For example, port 80 is HTTP, port 23 is
Telnet, and port 25 is SMTP.

Legalities

In the USA, no federal law prohibits scanning,
however, without permission: civil lawsuits
can occur and complaint to the ISP may get
you banned. In Europe, Finland deemed a port
scan as an attempt to break in and convicted a
17-year old. In some countries, it may be
illegal depending on the interpretation of the
law. Other parts of the world are the same, it
depends mostly on intent, but no law
specifically outlaws port scanning.

Port Scan Tips – get permission before you
scan and keep the scan tight, only scan what
you are 100% sure about. Understand open,
closed, and filtered. Understand the TCP Flags.
You should understand the three-way
handshake. Disable ping: find other methods
of verifying that systems are up. Remember
CSP+/Security+: Know the packets and
understand the TCP/IP model.

Port Scans Should Reveal – if a system is
active and responsive, what ports are open or
filtered? What services are running and what
information can be gleaned?

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