MCU Connection Failed (0x0020) 20.0

[Inxss]

Hello,
We are getting "MCU Connection Failed (0x0020)", when trying to start meeting using our production 3CX server.
On the test 3CX server everything works fine.

Both servers have Version 20.0 Update 5 (Build 527 Beta), but the test server has 3CX FQDN and the production server has Custom FQDN.
Maybe that's the point.

 

[NicholasP_3CX]

Does the production server have the MCU on-site? Or is it using the 3CX MCUs?

You would need to allow access to wmr.3cx.net to get the details of the MCU. If it is on-premises you should be OK with that outgoing.

If the MCU used is a 3CX one, you will also need to allow access to the MCU as well. This is outgoing traffic from your network

https://www.3cx.com/docs/manual/firewall-router-configuration/#h.id3ekyt6j2qs

 

[Emanuele Bizzarri]

Could you check if you are able to reach all the ips reported by:

nslookup v18-vc-qos.3cx.net

from your production pbx?

mcus are dynamically assigned and the pbx must be able to reach them. The firewall rules ont the pbx must be kept updated periodically because the ips of mcus can change

 

[Inxss]

Does the production server have the MCU on-site? Or is it using the 3CX MCUs?

You would need to allow access to wmr.3cx.net to get the details of the MCU. If it is on-premises you should be OK with that outgoing.

If the MCU used is a 3CX one, you will also need to allow access to the MCU as well. This is outgoing traffic from your network

https://www.3cx.com/docs/manual/firewall-router-configuration/#h.id3ekyt6j2qs

We are using using the 3CX MCU.All ports are configured.

 

[NicholasP_3CX]

Connection to the 3CX MCUs are outgoing, not incoming.

 

[Inxss]

Could you check if you are able to reach all the ips reported by:

nslookup v18-vc-qos.3cx.net

from your production pbx?

mcus are dynamically assigned and the pbx must be able to reach them. The firewall rules ont the pbx must be kept updated periodically because the ips of mcus can change

How can I check availability? ICMP results from both servers are attached.

 

[Inxss]

Connection to the 3CX MCUs are outgoing, not incoming.

All outgoing "drop" firewall rules are disabled for both servers.

 

[Emanuele Bizzarri]

You don't have to check availability, the mucs are available.
What you need to do is be sure that your firewall allows your pbx to connect to all these mcus on port 443.
Outbound connection from pbx to mcu.

 

[Inxss]

You don't have to check availability, the mucs are available.
What you need to do is be sure that your firewall allows your pbx to connect to all these mcus on port 443.
Outbound connection from pbx to mcu.

We have previously disabled outgoing rules for both servers, so we can assume that there are no prohibiting outgoing rules.

 

[Inxss]

So, issue has been solved. Thanks Emanuele Bizzarri for support!

1. We checked all connections to MCU from Production and Test instances and saw difference in wget query responses.
2. We decided to check the MTU parameters sequentially on all outgoing interfaces
   parameters MTU:

• PBX Virtual Machine - 1500
• Interface on Hypervisor - 1500
• interface on gateway - 1350 - that was issue to fix