port scan--"filtered" ports

[Naruto Uzumaki <ageofnaruto () gmail com>]

When performing TCP port scanning Nmap marks a port filtered if it
either gets an ICMP port unreachable or no response. Now, this could
be because either a firewall or the scanning host is generating ICMP
ports or silently dropping packets.

By marking them as filtered does it mean that there could be a service
running on these ports but that service is only accessible by internal
users or limited public IPs and blocked for other hosts?

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