Re: Filtered v. Closed v. Open

[Matt Howard <mhoward () hattmoward org>]

On Friday 19 September 2003 1:46 pm, Jonathan Sanders wrote:
> What is the difference between a filtered port and an open port?  One
> would automatically say the former is behind a firewall of some sorts
> right?  When doing a port scan using nmap, I had several come back
> saying 25/tcp was an open port, but after checking, the supposed host
> did NOT have SMTP service running.  So 25 being open just means the
> firewall is allowing that traffic right even though there's no service
> running on that port?  Guess my question is still what is the difference
> between filtered, closed and open ports.  Thanks...
>
> Jonathan

Closed means that nmap got a response saying that the port was closed; 
Filtered means that the SYN packet to open the connection was dropped or 
ignored and got no response.

-- 
Matt Howard <mhoward () hattmoward org>
http://hattmoward.org

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