Cannot register more than one IP phone using FQDN

[RickK]

Have an on-prem server (10.10.30.3)
Added one IP phone (T54W) using FQDN, hairpin is enabled and working on router. This works perfect.
Adding a second IP phone the same way, it will not connect. The only way I can get more than one phone connected is to use the IP# of the 3CX server.
If I configure both of these phones with the FQDN and reboot everything, the first phone that connects will be the only phone that connects. The other will fail.
I seem to be running into some sort of limit. Is that possible?
The FQDN resolves to the WAN IP of the router, but hairpin is enabled and I'm certain that it works (or the first phone wouldn't connect)

 

[SteveITS]

Haven’t tried, but if your router is using its IP 3CX may be seeing the connections come from the same IP.

I suggest split DNS instead. 3CX has posted it will be required.
https://www.3cx.com/docs/creating-fqdn-split-dns/
That doc equates it to hairpin NAT but it’s not using NAT.

 

[RickK]

Haven’t tried, but if your router is using its IP 3CX may be seeing the connections come from the same IP.

I suggest split DNS instead. 3CX has posted it will be required.
https://www.3cx.com/docs/creating-fqdn-split-dns/
That doc equates it to hairpin NAT but it’s not using NAT.

Thank you Steve!! I was following that doc but I guess I misinterpreted the concept of what seemed to be them recommending keeping the Prov URL consistent. I was concerned that by using IP# (which is clearly best option here) that the IP# would show up in Prov address for users setting up the app. Probably not the case? Last time I messed with 3CX was probably 20 years ago... just getting back into this now that some customers looking for a solution. Thank you Steve!!

 

[SteveITS]

It is saying to use the hostname internally, just have it resolve to the LAN IP in the office, and the public IP outside.