I don't have access to company firewall server. but supposedly the port 1720 is open on my one ubuntu server. So I want to test it with netcat:

sudo nc -ul 1720

The port is listening on the machine ITSELF:

sudo netstat -tulpn | grep nc

udp        0      0 0.0.0.0:1720            0.0.0.0:*                           29477/nc

The port is open and in use on the machine ITSELF:

lsof -i -n -P | grep 1720

gateway 980 myuser    8u  IPv4 187284576      0t0  UDP *:1720

Checked the firewall on current server:

sudo ufw allow 1720/udp

Skipping adding existing rule

Skipping adding existing rule (v6)

sudo ufw status verbose | grep 1720

1720/udp                   ALLOW IN    Anywhere

1720/udp                   ALLOW IN    Anywhere (v6)

But I try echoing data to it from another computer (I replaced the x's with the real integers):

echo "Some data to send" | nc xx.xxx.xx.xxx 1720

But it didn't write anything. So then I try with telnet from the other computer as well:

telnet xx.xxx.xx.xxx 1720

Trying xx.xxx.xx.xxx...

telnet: connect to address xx.xxx.xx.xxx: Operation timed out

telnet: Unable to connect to remote host

Although I don't think telnet works with udp sockets.

I ran nmap from another computer within the same local network and this is what I got:

sudo nmap -v -A -sU -p 1720 xx.xxx.xx.xx



Starting Nmap 5.21 ( http://nmap.org ) at 2013-10-31 15:41 EDT

NSE: Loaded 36 scripts for scanning.

Initiating Ping Scan at 15:41

Scanning xx.xxx.xx.xx [4 ports]

Completed Ping Scan at 15:41, 0.10s elapsed (1 total hosts)

Initiating Parallel DNS resolution of 1 host. at 15:41

Completed Parallel DNS resolution of 1 host. at 15:41, 0.00s elapsed

Initiating UDP Scan at 15:41

Scanning xtremek.com (xx.xxx.xx.xx) [1 port]

Completed UDP Scan at 15:41, 0.07s elapsed (1 total ports)

Initiating Service scan at 15:41

Initiating OS detection (try #1) against xtremek.com (xx.xxx.xx.xx)

Retrying OS detection (try #2) against xtremek.com (xx.xxx.xx.xx)

Initiating Traceroute at 15:41

Completed Traceroute at 15:41, 0.01s elapsed

NSE: Script scanning xx.xxx.xx.xx.

NSE: Script Scanning completed.

Nmap scan report for xtremek.com (xx.xxx.xx.xx)

Host is up (0.00013s latency).

PORT     STATE  SERVICE VERSION

1720/udp closed unknown

Too many fingerprints match this host to give specific OS details

Network Distance: 1 hop



TRACEROUTE (using port 1720/udp)

HOP RTT     ADDRESS

1   0.13 ms xtremek.com (xx.xxx.xx.xx)



Read data files from: /usr/share/nmap

OS and Service detection performed. Please report any incorrect results at http://nmap.org/submit/ .

Nmap done: 1 IP address (1 host up) scanned in 2.04 seconds

           Raw packets sent: 27 (2128B) | Rcvd: 24 (2248B).

The only thing I can think of is a firewall or vpn issue. Is there anything else I can check for before requesting that they look at the firewall server again?