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Documentation issue (-F)
From: Daniel Miller <bonsaiviking () gmail com>
Date: Thu, 12 Apr 2012 13:09:50 -0500

List,

From the man page:
-F (Fast (limited port) scan) .
Specifies that you wish to scan fewer ports than the default. Normally Nmap scans the most common 1,000 ports for each scanned protocol. With -F, this is reduced to 100.

Nmap needs an nmap-services file with frequency information in order to know which ports are the most common. If port frequency information isn't available, perhaps because of the use of a custom nmap-services file, -F means to scan only ports that are named in the services file (normally Nmap scans all named ports plus ports 1–1024).
Empirically, I see Nmap scans 1000 ports by default, 100 with -F, and <300 when nmap-services is not available. What is that last parenthetical statement about? Is this old info which should be purged?

Dan

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