Local network unable to access 3CX via FQDN or local URL (works only from external network)

[HSBN]

Hello,

Our local network users are unable to access the 3CX system using both the FQDN and local IP/URL. However, I can successfully log in from outside the network (using a different IP) as an admin.

Here are the details:

3CX is hosted on-premises.
External access (from other networks) works fine.
Local access (from LAN) fails — no login page or connection.

I have checked and there’s no IP in the blacklist under Management Console → Security → IP Blacklist.

I also allowed (whitelisted) the local IP, but it didn’t resolve the issue.

Restarted the internet router (which changed our public IP), still the same issue.

No Fail2Ban service visible on the server.

I cannot change the local network IP addressing scheme.

What could be blocking local access while external access still works?
Could it be a DNS / NAT loopback issue or a hidden firewall block inside 3CX or require to do anything from backend?

Any guidance on how to verify or reset local access from the 3CX backend would be appreciated.

 

[bitn2]

This is a local network problem, nothing to do with 3cx. Check your firewall and network for this.

Split DNS, firewall rules between the networks and so on...

 

[Alphabetic]

What is your network topology? What is your DNS server?

these specifics would help us give you better instructions to get you set up.

 

[HSBN]

Thanks, Its locally hosted on VM on NAS Drive.

Router -> NAS Drive (VM)

After disabling dual lan on NAS Drive, i was able to access 3cx from local ip.
But i cant access still from FQDN to which users were connected.

 

[Alphabetic]

What router?

assume this is also your DNS server.

 

[HSBN]

Yes its Draytek 2860
Yes its setup as DNS

 

[Alphabetic]

Great, now we're getting somewhere.

Go to Applications > LAN DNS and create a new one for your 3CX FQDN. use the internal IP



Be sure to check this box

 

[Alphabetic]

Just a thought.

You need to make sure your Draytek is giving out its own IP as the DNS server rather than your WAN DNS.

LAN > General > Details Page > DNS Server IP Set this to the IP of your router


**ignore the IPs in my screenshot.

You will use the same IP defined in the "IP Address" on the left.

 

[HSBN]

yes i tried, but no luck.
normally it was working fine without any issue, but later its stopped.

 

[Alphabetic]

tried what?

what endpoint are you using?

I need better answers to assist you.

internally, when you ping FQDN from command prompt, does it come back with the internal or external address?

 

[HSBN]

I tried your steps to add lan DNS config and given router IP to dns1 of lan setting, restarted router, still I can't access the page.

It feels like I was using 3cx year back, when this situation arises.

When I ping it still ping to public IP.
On the mobile app there is an option local and external, does it mean it will connect from ip when I'm in office and when I'm outside it connects through fqdn, will be it connecting same way from laptop

 

[Alphabetic]

There shouldnt be that option IIRC.

Update your app.

everything should be using FQDN.

Can do a quick remote session if youre free?

 

[HSBN]

Sure, we can do tomorrow morning at 9 am uae time

 

[Alphabetic]

This is 6AM for me, ill be zZzZzZ

 

[HSBN]

Sure no issue, take your time, im available now

 

[HSBN]

586 600 641

 

[Alphabetic]

586 600 641

wrong chat bro