Unable to get inbound calls on SIP trunk (Gradwell Communications)

[ALG-Antony]

Hi all, I'm a long time user and first time poster on here and was hoping you'd be able to assist.

I've configured V18 (and V20) instances of 3CX on prem. I can get the outbound working perfectly fine however inbound doesn't seem to want to. I can see on my router the tcpdump log of all traffic being routed from the port forwarding rules to the 3CX server however I can't see anything on the 3CX server itself. I've tried multiple different authentication settings between my provider and SIP trunk. I've contacted the friendly people at Gradwell and they also tried assisting to no avail. It's like the server can't recognise the packets.

I can provide tcpdumps if required. Does any one know of something obvious, like a setting on the PBX that would allow it to accept these invite packets?

 

[Alejandro_3CX]

Hi Antony, so you took a capture in the 3cx and you don't get any traffic from the voip provider?

what is the firewall checker result?

are you using the default template?

did you install the pbx using a different SIP Port rather than 5060, if so is the provider sending the packets to the pbx public ip and the correct sip port?

by chance check the blacklist and validate that there is not any ip blocked, set the provider ip as whitelist.

 

[VoIPTools]

If you can make outbound calls, we know you have successfully authenticated to the SIP provider. That's good.

If this was a configuration error with inbound rules, then my assumption would be that all calls would simply go to the main route. Keep in mind that inbound rules that specify the route for a specific DID should typically only specify enough digits to make the route unique. For example, If my DID was 8016424655, your rule might specify something like *8016424655 or even *6424655. The wildcard will ignore preceding characters sent to you by your carrier (example: +18016424655). Again, I doubt that is the problem since there is typically a default route for any calls that do not match one of the inbound rules.

If the wire capture suggested by @Alejandro_3CX (taken from the PBX) does not show any inbound SIP requests coming from your SIP provider, I think it is a safe bet that there is still an issue with your routing configuration in your firewall. Let's not forget that if your PBX is running on Windows, there is a Windows firewall too!

 

[ALG-Antony]

Hi both,
Thank you for getting back to me.

To clarify I have deployed both 3CX servers from the Debian image available on the 3CX portal

Hi Antony, so you took a capture in the 3cx and you don't get any traffic from the voip provider?
I do get traffic from the VOIP provider as reported on my firewall however there's no traffic on the 3cx server
what is the firewall checker result?
The firewall checker within the admin portal shows a green tick
are you using the default template?
Yes, I'm using the basic one provided by 3CX
did you install the pbx using a different SIP Port rather than 5060, if so is the provider sending the packets to the pbx public ip and the correct sip port?
No, I used the default SIP port. It was only the http port I changed
by chance check the blacklist and validate that there is not any ip blocked, set the provider ip as whitelist.

There are no IPs on the blacklist. I've also had the originating IPs to the whitelist

I ran the tcpdump and filtered port 5060 and got the following whilst I attempted to make a call to the DID number. It's the same 5 lines repeated over. Is it weird that it's registering SIP on 127.0.0.1? Or is that standard? I would have thought it'd attempt to register on the local IP address.

Spoiler: TCPDump from 3CX Server

root@souvp3cx01:~# tcpdump -i any port 5060 -n
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
23:20:34.097448 IP 127.0.0.1.5063 > 127.0.0.1.5060: SIP: REGISTER sip:127.0.0.1:5060 SIP/2.0
23:20:34.197980 IP 127.0.0.1.5060 > 127.0.0.1.5063: SIP: SIP/2.0 407 Proxy Authentication Required
23:20:34.298505 IP 127.0.0.1.5063 > 127.0.0.1.5060: SIP: REGISTER sip:127.0.0.1:5060 SIP/2.0
23:20:34.398929 IP 127.0.0.1.5060 > 127.0.0.1.5063: SIP: SIP/2.0 200 OK
23:21:04.500159 IP 127.0.0.1.5063 > 127.0.0.1.5060: SIP
23:21:20.232309 IP 127.0.0.1.5483 > 127.0.0.1.5060: SIP: REGISTER sip:127.0.0.1:5060 SIP/2.0
23:21:20.332726 IP 127.0.0.1.5060 > 127.0.0.1.5483: SIP: SIP/2.0 407 Proxy Authentication Required
23:21:20.370182 IP 127.0.0.1.5483 > 127.0.0.1.5060: SIP: REGISTER sip:127.0.0.1:5060 SIP/2.0
23:21:20.470619 IP 127.0.0.1.5060 > 127.0.0.1.5483: SIP: SIP/2.0 200 OK
23:21:28.483737 IP 127.0.0.1.5483 > 127.0.0.1.5060: SIP