Nmap filtered ports from BT4 virtual machine

[hyrasx]

I am doing a pentest on a friend's server, and from my main OS (ubuntu), nmap shows a few open ports, but from a Backtrack 4 I have in a virtual machine (virtualbox), I get the same ports filtered.

Does someone knows why this happens and if it can be "fixed"?

[pentrite]

If the ports appears open, the ports are in use or iptables bad configured.
In your case you give very less information. My answer is i dont know.
Did you run nmap from VM and Ub at same time? What scan?
...

[Archangel-Amael]

Just because a port is open does not mean that it is not filtered.
It would do you well to look into the nmap documentation.

[hyrasx]

I will try explaining more my situation.

As I understand, a simple port scanning would first send a SYN probe packet, then if it receives a packet with SYN and ACK flags, the port should be open but if it receives a RST/ACK packet then the port is close. Now, filtered ports don't receive neither a SYN/ACK or a RST/ACK packet back after the first SYN packet is sent (not sure if this is correct), and what cause this most of the time is a firewall on the other end.

So, I am doing a simple scan on the target server with

nmap <HOST> -v

From my main OS (ubuntu 10.04), I get the port 80 open, which means I am receiving a SYN/ACK packet. But when I try the same scan from BT4 (installed in a Virtualbox VM), the result shows the same port as filtered, so nmap is not receiving a SYN/ACK packet as response.

On the BT4 virtual machine, I connect to the internet using Network Adapter > Attached to > NAT, I just run "/etc/init.d/networking start" and it works fine, I never configured anything else.

I was wondering if I should configure something to get nmap working on the virtual machine as it's working on the main OS, I can't figure out what could be causing this and I couldn't find any info on google about this "problem".

Btw, I am not running the scans at the same time on Ubuntu and BT4.

[roybatty]

You don't understand the implications of using Virtualbox NAT. Use bridged networking instead. http://www.backtrack-linux.org/forum...map-issue.html