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We were trying to install "Big blue button" in an Ubuntu server with a firewall. For installation, we need these UDP ports ("16384-32768") should be opened in the firewall. But we don't know whether the udp ports are opened or not in the firewall. When we tried the "netcat" service, we were able to communicate. But while doing "nmap" scanning, it has been showing these UDP ports in the state as "closed"

nmap command used as :

 nmap -sS -sU -PN -p 16384 EXTERNAL_IP ( For single port )

Output :

   Host is up (0.039s latency).

   PORT      STATE    SERVICE
  16384/tcp filtered connected
  16384/udp closed   connected
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Like most VoIP services, these ports are dynamically opened during the call and are not permanently open. Since you have already checked if you can reach these ports on your server with netcat there is no further need to verify if these ports are open.

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  • We are using a webrtc based application inside the firewall.But when i checked the log file, the application complains that these UDP ports were blocked by the firewall. – aks Jun 8 '20 at 14:28

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