SBC's on multiple subnets (or not)

[popfindlay]

I'm currently using a hosted VOIP provider and I'm just beginning to study hosted 3CX as I think about maybe making a change.

We have a main office with 50 phones and six remote locations with 2 phones each. All remote locations are connected to the main office and get their Internet from there. Meaning, all traffic goes out the door from the same public IP address.

If I put Pi's in all the remote locations, and something bigger in the main office, will there be a problem with that many SBC's hitting the 3cx cloud server from the same public IP address? Or should all the remote phones connect to the main office SBC? The firewall is obviously NATting outbound traffic.

 

[Saqqara]

I believe you can have as many sbc servers as you like.

Do,you have vpn between the remote office and the main office - if so I would probably setup the remote phones to use the main office sbc

To add some redundancy you could install more than one sbc server at the main office, and spilt the phones between the two sbc servers

Look at the system spec for sbc server , looking at the number of phones and blf keys https://www.3cx.com/docs/recommended-hardware-specifications-for-3cx/

 

[jpatel]

How are the remote sites connected? VPN tunnels via local firewalls?, or is it more ISP layer tunneling, like MPLS network?
I ask, because I am wondering about bandwidth considerations.
If bandwidth is not great, it might be better (if possible) to have SBCs at each remote location and to allow the remote SBCs alone to split over public ISP network to the PBX.

But if site-to-site tunnel allows decent bandwidth and same local subnetting as the main branch, theoretically a single SBC (or even PBX if you're not doing cloud hosted, and wanting to do self hosted) at the main branch should be sufficient. (i,e if SBC is located at the main branch with local IP 10.0.0.200/24 and remote phone is 10.0.0.201/24, then you shouldn't need SBCs at each location).

 

[ChrisC_3CX]

If I put Pi's in all the remote locations, and something bigger in the main office, will there be a problem with that many SBC's hitting the 3cx cloud server from the same public IP address?

I believe you can have as many sbc servers as you like.

This I can confirm and and to clarify, yes the can all be behind the same public ip.

Something else I'd like to add to what has already been said is that, if the IP Phones are not on the same subnet as the SBC, multicast will not reach the SBC from the IP Phones (unless you are forwarding it somehow on the network level) hence you will not be able to see the IP Phones in the Management Console's Phones section to provision via PnP.

 

[popfindlay]

It's 20Mb fiber MPLS at all the remotes. Different subnets. I believe I can tell the remote phones about a main office SBC via option 66 in DHCP.

It sounds like I can do it either way. But spending a bit more on one big box may be preferable to having a lot of little boxes to deal with, especially if they're far away (they are).

ChrisC, if I've used a DHCP option to tell the remote phones about an SBC in another subnet, would that negate your comment about not being able to see the phones in the management console due to multicast being blocked?

 

[Saqqara]

Dhcp Option 66 , you add the provisioning url , not the sbc server address . https://www.3cx.com/sip-phones/DHCP-option-66/

You add the phone manually into 3cx management console, configuring to use sbc server.

Next time you restart the phone, it should connect to the provisioning url and configure the phone

You do not need multicast, if you setup dhcp option 66 and add the phones manually into 3cx

 

[jpatel]

Also note, in the DHCP option 66 article mentioned, that not all DHCP servers are capable of this. If you don't have it, the idea of an SBC on Pi at each location sounds appealing or an unused repurposed desktop. At least for PnP.

But if you're willing to put the a little more work in, and there are semi tech-savvy users at each remote site. Maybe a remote STUN (Direct SIP) option might work for those.

Phones at remote site would have local static IPs with dedicated local SIP port (per phone), and an RTP port range port-forwarded to the PBX. When it comes time to plug in, phones receive the STUN signal and you provision the phone by entering username (ext number) and VM pin as password. Of course main site would be a normal SBC to make life easier with PnP.

 

[ChrisC_3CX]

STUN would work but I would recommend against it especially since you already have an SBC setup. using the SBC in conjunction with DHCP option 66 should be fine as long as you've first manually added the IP Phones into the Management Console as SBC phones. You still won't be able to utilize PnP hence the requirement to add them manually first, but, with Option 66 you'll at least be able to get them provisioned again even if they are factory reset. You will also still be able to push a re-provisioning command via the 3CX Management Console.