Error 0x0020 at the power of a conference

[itlycoon]

Hi everyone!

I need some help with an error that happening when my client try to start a conference / instantanely reunion, he have an error 0x0020 with a message that say "MCU Connexion Failed".
Before that, the conference worked correctly since a long time.
I can't reboot the system when I want because of the many call that my client have.
I try to contact the support but they want a capture of the same problem with the supportinfo file and I can't make it currently.
And in the forum all the people with the same problem are redirected in the 3CX support so I don't have any informations of this problem.

Thank you for your feelback.

Sincerly

 

[NikosT_3CX]

@itlycoon if you go on the Admin Console >> System >> Conferencing >> Video >>
Select your region, what is selected there ?

 

[itlycoon]

It's EUROPE so it's correct, and we don't touch that.

 

[Yetiman]

@NikosT_3CX same issue here since today, region also Europe. Our PBX sends the TCP SYN to the MCUs but never gets a SYN-ACK back, while a neighbour IP in the same subnet reaches them instantly. Looks like the MCUs are dropping certain PBX IPs. Details + packet capture:

Thread 'MCU Connection Failed (0x0020) since 06 Oct – MCUs silently drop TCP 443 from our PBX IP only'

Today at 1:00 PM

Hi all,

Since 06 Oct 2026, every web meeting on our PBX fails with MCU Connection Failed (0x0020). It worked until 05 Oct, and nothing was changed on the PBX or the firewall.

Setup: V20 Update 9 (Build 995), PRO, on-premise Windows, Hetzner DC Nuremberg (DE), MCU region Europe, public IP 46.4.220.249 (static, 1:1 NAT).

What we tested:

• From the PBX, TCP 443 to every MCU currently returned by v18-vc-qos.3cx.net fails (e.g. 159.223.93.4, 35.247.196.146, 34.35.69.212, 34.35.67.34, 34.176.3.76, 157.245.108.209, 188.166.157.144, 167.71.231.53)...

• Yetiman
• Replies: 0
• Forum: Video Conferencing

@itlycoon quick check from your PBX (PowerShell): Test-NetConnection 159.223.93.4 -Port 443. If it shows False while other websites work, it's the same issue.

 

[itlycoon]

So this noon I have reboot the 3CX System and after this I had a response of the 3CX Support with a correction :
"we found an issue with a specific MCU where you connected to.
We have shifted the traffic from this one to others and a fix has been applied already.
Please check it further and if anything occurs let us know. "
I called my client and we make a visio-conference without problem.

So it's the 3CX Support that resolve the problem.

Thank you for your feedback and good luck!

Sincerly