When scanning my public ip address with
Nmap I found out that I have open port on
1720/TCP. According Nmap service on it is
H.323/Q.931. Researching uses of this port also brings up Microsoft Netmeeting.
I did the scan from outside, not from my own network.
My router/modem is
ZyXEL P-660HN-T1A, ADSL2+. The modem is in routing state and devices behind it are using
NAT. Devices behind the modem are Windows 7 computer that was turned off during the scan and Linux server that is listening only on
22/SSH. On the settings of the modem port forwarding active only for the SSH port. As far as I can see from the settings, there is no remote management allowed from
So why does port
1720 appear open on Nmap scan? Is this some feature of the modem or could this mean some kind of security breach?
EDIT: I did the same from my home computer to my public IP. From this point of view the port 1720 is not open. Does that tell something?
EDIT2: From the settings I found out that UPnP was enable for LAN only. I don't have any VOIP services. I am not aware of my ISP managing my device. (They did not provide the device.)
EDIT3: Telneting my public ip and port
1720 from the outside connects:
Connected to <my ip> Escape character is '^]' <giving any input> Connection closed by foreign host.
EDIT4: More scanning revealed that I also had port
7547open (Allegro RomPager according to Nmap). It even provided html page accessed from the internet.