Filtered ports

Dear all,

I used scan port software to scan the ports of my fixed IP line.

I find most ports are "filtered" and only pop3 port is open. What is the meaning of filtered port?


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It means that your packet filter is dropping connection attempts instead of rejecting them.


Reply to
Ansgar -59cobalt- Wiechers

Well, the documentation of the software you have used should explain what "filtered" means. You don't mentioned which software you have used thus I can only guess that "filtered" means that the software did no get any response when it tried to connect to those ports.

This is usually because some firewall blocked the response which the computer sends when someone tries to connect to a closed port. Quite a lot of people strongly believe it is extremely important to block those responses in order to be "stealth" and it sells good...


Reply to
Gerald Vogt

man nmap, if you have it and it describes its tests and responses in great detail. To have a better constrained question, you'd have to specify what type of scan you were performing because the specifics of how the target responded are inferred differently depending on whether you did a full tcp connect scan, a syn scan, an xmas scan, etc.

In the 3 way tcp handshake, if the scanner sends a SYN, and the target does not respond with anything, the port is reported as filtered. Likewise, if a TCP SYN is sent to the target, but the target responds with ICMP destination unreachable, or administratively prohibited it's also considered filtered.

Simplistically, think of filtered as good--it's what ya want. Closed is decent, but the port is actually responding to the scan, which draw more attention from attackers who might shortlist it to try again later to see if something might come up on the port.

Another term you'll see for filtered sometimes is "stealthed."

Best Regards,

Reply to
Todd H.


Coined by a sensationalist watching too many science fictions and adopted by marketing.

Reply to
Straight Talk


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