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I am investigating how to open a UDP port, specifically the port 1194. This is what I've done:

  1. Check if the port is opened:

    % sudo nmap –sU –p 1194 <hostnameOfMyMachine>
    
    -> PORT     STATE  SERVICE
    -> 1194/udp closed unknown
    
  2. Open the port:

    % sudo iptables -A INPUT -p udp --dport 1194 -d 0/0 -s 0/0 -j ACCEPT
    

Finally, I repeated the step 1) to check if the port has been opened but the same output is displayed:

-> PORT     STATE  SERVICE
-> 1194/udp closed unknown

Does anybody know why the port did not open? How can I open it?

% sudo netstat --inet --inet6 -lnp

Conexiones activas de Internet (solo servidores)
Proto  Recib Enviad Dirección local         Dirección remota       Estado       PID/Program name
udp        0      0 0.0.0.0:41503           0.0.0.0:*                           1372/avahi-daemon: 
udp        0      0 127.0.0.1:53            0.0.0.0:*                           2344/dnsmasq    
udp        0      0 0.0.0.0:68              0.0.0.0:*                           2303/dhclient   
udp        0      0 0.0.0.0:17500           0.0.0.0:*                           5935/dropbox    
udp        0      0 0.0.0.0:17500           0.0.0.0:*                           6025/dropbox    
udp        0      0 0.0.0.0:5353            0.0.0.0:*                           1372/avahi-daemon: 
udp6       0      0 :::44533                :::*                                1372/avahi-daemon: 
udp6       0      0 :::5353                 :::*                                1372/avahi-daemon: 


% sudo iptables -L INPUT -nv

Chain INPUT (policy ACCEPT 134K packets, 19M bytes)
 pkts bytes target     prot opt in     out     source               destination         
    3    84 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:1194
    0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:1194
    0     0 ACCEPT     udp  --  *      *       0.0.0.0/0            0.0.0.0/0            udp dpt:1194
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  • 4
    To open UDP port 1194 you need an OpenVPN-shaped crowbar. Sep 2, 2017 at 9:09
  • Someone suggested me to install the software OpenVPN and I wonder if I can open the port using this software. I don't know what OpenVPN-shaped crowbar is...
    – birdman
    Sep 2, 2017 at 9:23
  • What is the output of sudo netstat --inet --inet6 -lnp and sudo iptables -L INPUT -nv? Sep 2, 2017 at 9:27
  • 1
    Why do you want to open UDP port 1194? Sep 2, 2017 at 9:44
  • 2
    If you are asked for additional information then you should edit your question and add it. I have done that this time. These commands show that the firewall does not block UDP/1194 but (as others have already guessed) there is no application (i.e. OpenVPN) using that port. Sep 2, 2017 at 13:59

2 Answers 2

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A UDP port is considered open by nmap if a packet sent to this port results in a reply from this port.

This, of course, means, that there needs to be some service running at the port. Port 1194 is typically OpenVPN.

Even if there is some service running at that port, it might be considered closed if a firewall is filtering packets to or from this port. That's why you've tried to add a rule to the firewall (iptables) to let these packets pass.

But this rule does not help if there is no service running on this port in the first place.

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  1. You need to put this port rule to your router and forward it to your machine.

    (If that is a VPN application, there is, of course, no need for port-forwarding.)

  2. You need to configure whatever application for that port.

  3. That application must be running.

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