How does nmap/zenmap determine a port is filtered?

Posted on 2009-04-23
Last Modified: 2013-11-16
How does nmap/zenmap determine that specific ports are "filtered" as opposed to just not being presented via a daemon on a host?
Question by:amigan_99
    LVL 12

    Accepted Solution

    Nmap returns a "closed" status for a probe that receives a RST in response to a connect request. If there's a firewall in the way (either on the host itself or as a network device), a different response is returned, or none at all if the packets are simply dropped, generally resulting in a "filtered" status.. The Nmap page at lists the various status values that can be returned.

    Nmap has many different port scanning techniques to try to derive more information from the scan.They're documented in
    LVL 1

    Author Closing Comment

    Excellent - thank-you!

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