Solved Failed to send APNS PUSH to device iPhone15,2iPhone(Ext.999). Internal exception occured: The SSL connection could not be established

[shanec24]

Hi All,

Apple devices do not receive the notification of an incoming call. This error is logged in the console: Failed to send APNS PUSH to device iPhone15,2iPhone(Ext.999). Internal exception occured: The SSL connection could not be established, see inner exception. It works fine for desktop phones & Android devices.

By testing the network/internet access ourselves and running a packet capture ,we have confirmed that that:

• The PBX does have working DNS (using Google 8.8.8.8). They do query and resolve the URLs for Apple's push notification service and Certs. They get the correct results back which match lookups against public DNS servers.
• PBXs are not trying to use IPv6.
• PBXs do actually connect to Apple push notification service and start a TLS session etc etc.

End to end connectivity to Apple servers is working. We can see that from the packet capture.

The firewall checker passes.

The PBX's do not have any outbound internet restrictions, nor any form of SSL inspection/certification inspection/web filtering/intrusion detection/etc. Direct internet access. Public IP is directly on the VM itself as well.

The PBX are running 18.0 Update 9 (Build 20) on Debian installed from ISO and use a *.3cx.com.au FQDN.

See here normal network connectivity to Apple when a call is made with DNS query, cert checks and connection to Apple APNS:

 

[shanec24]

Solved.

We managed to identify an MTU issue in the path of one of the upstream internet providers beyond our network on their connectivity to Apple in Sydney AU. This is why we were able to see normal routing and connectivity. Some packets were being dropped.

 

[TheodorosG_3CX]

@shanec24 Glad to know this is resolved and you shared this information.
Since the connectivity from/to the PBX is correct this has to be checked further(e.g ISP).