3CX 15.5 and SBC Subnet question

[RClark]

I have a main PBX in a Head Office that works great.
I have now setup an SBC to be used with 4 phones at a remote office.
The remote office is a shared space so I do not have control of the subnet.
The subnet happens to be the same as the head office 192.168.0.xxx
So the SBC has an address of 192.168.0.xx
The sbc connected no problem with the pbx and when I plug a phone in it appears in the main pbx within 30 seconds.
However the phones will not provision and I am thinking it has to do with both the sbc and the main pbx server being on the same subnet 192.168.0.xxx
Any thoughts on this would be appreciated as well as any work arounds if my assumption is correct.

 

[AWS2P]

Have had same question in the past, French 3cx support answer me that Ip range has no effect if it's the same in local and remote.
But i've done a lab tests and like you i encountered some problems for phones to be provisionned. every thing run fine when ranges are not the same. This is my conclusion

 

[RClark]

Is there a way to manually force provision and have the phones then work OK?
It is only 4 phones.

 

[Evolute IT]

Is there a way to manually force provision and have the phones then work OK?
It is only 4 phones.

Why are you using an SBC if the PBX is local?

 

[RClark]

The PBX is local. The sbc is at a remote site

 

[RClark]

To be clear each location is using the same subnet range but are separate.
Both are 192.168.0.xxx

 

[Evolute IT]

To be clear each location is using the same subnet range but are separate.
Both are 192.168.0.xxx

This is the worst setup. The remote site or local site should use another subnet.

You can also add a router in the remote network and plug your things in it with your own DHCP and IP range. This way, you use the already-there-but-no-control network only as a WAN.

 

[cobaltit]

This is the worst setup. The remote site or local site should use another subnet.

You can also add a router in the remote network and plug your things in it with your own DHCP and IP range. This way, you use the already-there-but-no-control network only as a WAN.

It's not ideal but not really an issue unless you are doing a site to site VPN. I haven't done any testing like @aws2p but it really shouldn't be an issue. You don't mention which phones you are using but the most common issue when they won't provision is they are on older firmware that doesn't support the LE cert used by 3CX (assuming you are using a 3CX FQDN). Make sure the phones are on the latest 3CX supported firmware. The other potential issue is if you are running internal DNS that is resolving the FQDN of your 3CX to an internal IP. Since both sides are on 192.168.0.x subnets this could cause the problem. To test, ping the FQDN in the provisioning URL and confirm it resolves. And I'm assuming you already ran the firewall checker but if the HTTPS port isn't forwarded to your 3CX instance you also won't be able to provision.

 

[AWS2P]

@cobaltit
my test was done with snom deskphones up to date, the problem seems coming when you already have a local phone using an IP adress and want to provision another phone with same IP on remote side behind SBC.
I've not investigate more to understand if it's network problem or ambiguous situation for 3CX system, but surely when the IP range are not the same every thing is working fine with no delay to provision the same phones.

So for me question is solved , and the simplest way to be sure it works is to use different range on each side.

 

[JohnS_3CX]

I have a main PBX in a Head Office that works great.
I have now setup an SBC to be used with 4 phones at a remote office.
The remote office is a shared space so I do not have control of the subnet.
The subnet happens to be the same as the head office 192.168.0.xxx
So the SBC has an address of 192.168.0.xx
The sbc connected no problem with the pbx and when I plug a phone in it appears in the main pbx within 30 seconds.
However the phones will not provision and I am thinking it has to do with both the sbc and the main pbx server being on the same subnet 192.168.0.xxx
Any thoughts on this would be appreciated as well as any work arounds if my assumption is correct.

Hi RClark

The phones appear on the MC via the SBC. As soon as you assign a phone to an extension, the SBC will tell the phone to contact your FQDN via your HTTPS port and connect to the provisioning server in your PBX. Things that may fail and you should check first before making any assumptions are:

• HTTPS port of PBX must be reachable by phones
• Phones must support the TLS level and certificates 3CX uses
• Phones must be on latest supported 3CX firmware and default templates used
• Firewall at phones site must not block any of the above traffic or malform TLS in any way
• Firewall test at PBX end must pass the check

You need to eliminate all the above first, I suggest you start by connecting a PC on the same network as the phones, and trying to download a config file from the PBX. If that doesn't download then don't waste any time on other matters unless this is resolved first.

What phones are you using and what firmware version are they on?