Solved Incoming calls not working unless outgoing call is made first???

[Mark Drabble]

Currently running v15.5 (waiting to install v16)
Windows 2016 Stnd with all updates including .net 4.8
Gamma SIP Trunks

Have a bit of a strange issue which has recently appeared where our internally host 3CX server will not accept external incoming calls unless an external outgoing call is made first.

When someone tries to call our external number, the call connects - (can see details from firewall connecting to internal 3CX server and have captured data with wire-shark but no idea what I am looking for in wire-shark other than I can see the SIP Trunk IP address) but nothing happens....... no ringing, no IVR - just silence.

If I make an outgoing call from 3CX to any external number, we can receive incoming calls for a short period before the same thing happens again.

Only think I can think of is recent Windows Updates being applied.

Anyone else come across this before?

Cheers

 

[YiannisH_3CX]

Hello @Mark Drabble

What you are describing looks like a firewall issue that needs an outbound connection to be first made before it allows inbound connections. And i assume that if you do not make outbound calls for some time the issue comes back.
Run a capture on the 3CX server once the issue appears and make an inbound call. See if it is hitting the 3CX server. Also run the firewall checker (i suspect it won't show any issues but worth a try) and see if that passes.

 

[Mark Drabble]

Thanks for the reply.

Firewall checker reports all ok on 3CX and not made any alterations to my Firewall.

I'll try and watch for a quiet spot to see when it happens.

 

[Mark Drabble]

Looking at the firewall traffic I can see incoming calls being redirected to my 3CX server - however, on wireshark, I am not seeing traffic hitting the server.

Think I will raise a support call with the firewall people to see if they can spot something I have missed.

 

[Mark Drabble]

Still waiting on the Firewall people to contact me.... in the mean time I took a proper look at my firewall rules and noticed I had IPS enabled on the 3CX rules.

I have disabled and I am waiting for a period of no calls so I can test.

 

[Mark Drabble]

Happy to confirm the disabling IPS on my 3CX firewall rules has resolved the issue - having looked back at previous configs it turns out IPS was enabled 2 weeks ago which explains why it suddenly appeared.

 

[YiannisH_3CX]

Glad to see the issue has been resolved and thank you for updating the thread with your solution.