Ho to use NMAP to check if a port is filtered by a firewall?

Question

I have the following situation. I should have the access to a VM via SSH but trying to connect to this machine I obtain no response. I suspect that some firewall rules are blocking my request (so it should be considered as filtered).

How can I correctly use NMap (or some other tool) to check if the connection to the 22 port is filtered to discover if it is a firewall issue?

score 2 · Accepted Answer · edited Aug 27 '23 at 15:47

Does the VM respond to a ping ?

if not, where does a traceroute stops at ?

Nmap can only tell you if the port is closed(TCP FIN), open (TCP ACK) or filtered(no response), not where it is filtered.

You might want to check the logs / tcpdump on the vm to see if it sees the TCP SYN. Also check the logs on the firewalls between you and the VM.

Edit: nmap -sS -p 22 [VMIP]

-sS : Syn scan

-p 22 : port 22

Ho to use NMAP to check if a port is filtered by a firewall?

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