Nmap

h4z · 11-28-2004, 07:26 AM

I need your help guys , i am trying to use nmap on yoper , but it seems the GuardDog is blocking its port , i just need to know which port must i let access so that nmap can work

steve_v · 11-30-2004, 01:01 AM

Nmap by it's very nature scans the ports you tell it to scan. It is a port scanner after all :-)
So... If you want to scan port X on a remote machine, you need to unblock port X on yours.

I sincerley hope you are not one of those try hard "hackers", if you don't know what nmap does or how it works then you don't need to use it. No offence intended if you have a legit reason to be port scanning people :-)

Steve.

kernowyon · 11-30-2004, 07:13 AM

Quote:

Originally posted by steve_v
Nmap by it's very nature scans the ports you tell it to scan. It is a port scanner after all :-)
So... If you want to scan port X on a remote machine, you need to unblock port X on yours.

I sincerley hope you are not one of those try hard "hackers", if you don't know what nmap does or how it works then you don't need to use it. No offence intended if you have a legit reason to be port scanning people :-)

Steve.

Seconded

Nmap is a very useful program, but it can also be used for less useful purposes - as can any of the port scanning tools available.
Its worth remembering that if you decide to scan outside your own network, then any half decent sysadmin will detect your attempts and report any unrequested scan to your ISP - thus losing your account . Always ensure you get written permission from whoever is in charge of any network you scan - its very easy to end up accused of illegal activities.

Bebo · 12-07-2004, 10:30 AM

Quote:

Originally posted by steve_v
So... If you want to scan port X on a remote machine, you need to unblock port X on yours.

This is not true. The outgoing port on the machine where nmap is run does definitely not have to be the same as the one you scan. You would need a lot of ports open for that

What you do need is a firewall which lets out (in iptables lingo) NEW and, in fact (since nmap can construct really odd packets for certain scan modes), INVALID packets, and lets in ESTABLISHED and (for nmap purposes possibly, for general purposes definitely) RELATED packets. Of course a firewall like this would not be very useful unless you also let out ESTABLISHED and RELATED packets.

This sets up a rudimentary iptables firewall for a stand-alone box not running any services:

Code:

iptables -P INPUT DROP
iptables -P OUTPUT DROP
iptables -P FORWARD DROP

iptables -A OUTPUT -o lo -j ACCEPT
iptables -A OUTPUT -o eth0 -m state --state NEW,ESTABLISHED,RELATED,INVALID -j ACCEPT

iptables -A INPUT -i lo -j ACCEPT
iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT

steve_v · 12-09-2004, 02:09 AM

I stand corrected :-)