Nmap showing closed ports as opened

Posted at October 23, 2015 at 8:28 am by InterServer Staff

Nmap may show closed ports on your server as opened if you are scanning from a natted system or behind a firewall. For example:


1720/tcp open H.323/Q.931?
3128/tcp open squid-http?
8080/tcp open http-proxy?


The following open ports showed opened on a system but were not listening on the server itself. It turns out it was a proxy from the ISP and the ports showed open on any server.

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