[ILUG] nmap -- Port Searching

[Francis Daly]

2008/10/5 Frank Murphy <frankly3d at gmail.com>:
> Trying to find a suitable unblocked port for my torrents ( linux :) )
> How can I try a range of ports say 45000 50000 both udp and tcp (azureus)
>
> have tried : nmap -p t:45000-50000 u:45000-50000 ***.***.***.*** (isp
> assigned ip)
>
> but can't seem to get nowhere, just says host is up,
> but would like a list of usable ports.

Out of interest, does "netstat -pant | grep LIST" on your PC show that
there is something listening on tcp ports 45000-50000? Because if you
haven't got a server listening there, the nmap client won't be able to
connect to it.

To check if the port is blocked by a firewall outside of your control,
run something like netcat listening on your PC (nc -l -p 14774), and
then from a remote machine "telnet your_ip 14774" and see if it
connects. (Type something in the telnet window and it should appear in
the nc window, if it has connected.)

Or ignore the listener, and just get tcpdump or something similar
running on your PC, telnet in from afar, and see if the traffic gets
to you.

If you're using a firewall that you do control, check whether it
allows inbound services at all; or check whether you have a "default
DMZ server" or something similar configured -- for any inbound
traffic, is there something in your control which prevents it from
getting to your machine?

"iptables -L -n -v" doesn't show anything obvious like a large number
of rejected packets at the end, or anything like that, I guess?

Good luck,

f