Internal IP to support failover

[Jon Gair]

Just trying to get my head around the failover configuration and the implications on the internal IP address on a standby server.

I can understand the concept of one DNS name which can be switched between two different public IP addresses via a short TTL. However, it would appear that the configuration points for the internal server IP only has one option (rather than two as per the Public IP) so this IP setting would need to be the same on both servers (active and standby). Specifically, the SBC 3cxsbc.conf configuration file for the SBC only has one entry for the internal IP address of the server via the PbxSipIP field. I suspect the SBC needs to know the internal IP address of the server to ensure the SIP packets within the tunnel are created appropriately to support going through NAT. However, it means that both the servers would have the same internal IP address so they will not be able to communicate with each other if hosted on the same LAN. Other option is to change the standby server to match the active server via a script if it is ever failed across.

Can anyone confirm the technical detail around this one ? I cannot see it in any of the documentation.

Thanks.

Jon

 

[YiannisH_3CX]

Hello @Jon Gair

Please let us know of your configuration and how the phones will be provisioned to the server.
Is the PBX local or hosted? Are you using local or remote extensions? Where will the failover server be located?

 

[Jon Gair]

I have a test enterprise edition server setup in Azure with a public IP and internal IP of 10.0.0.4. Just considering the design of having a standby server and any limitations, I am finding the documentation a little unclear.
I can create another Azure 3CX VM in a different region for the standby and potentially manage them both and have the FTP backup/restore traffic on the internal network to make it more secure. I am just thinking this will be a problem if they both have the same internal IP since there will be a conflict and they will not be able to route traffic correctly. I have a number of sites and I am expecting to use an SBC at each site to tunnel the traffic.

Thanks

Jon

 

[cobaltit]

Honestly I would handle the failover in Azure at the VM level instead of relying on 3CX.

 

[Jon Gair]

Thanks. Sure there are multiple different ways of obtaining resilience and redundancy. Just keen to understand if the internal IP needs to be the same on the standby server since it will effect the overall design. The documentation appears to be unclear.

 

[YiannisH_3CX]

The internal IP does not need and should not be the same for failover to work. In the SBC setup you need to enable the failover option and add the second server.

 

[Jon Gair]

Thanks, but I am still a little confused. The SBC documentation states that "If the 3CX Phone System is behind a NAT enter the local IP." but there is no option for 2 local IPs in the GUI or the .conf file (there is for the public IP or just use dns so it can be changed)

https://www.3cx.com/docs/3cx-tunnel-session-border-controller/

If the standby server has a different local IP to the active, how will the SBC software be aware that the local IP address has changed if it is ever put into operation (the public IP will be fine)

 

[YiannisH_3CX]

The SBC tries to connect to the public IP of the PBX through the tunnel port. Once the primary server goes down and the DNS updates to the new public IP then the SBC will try to connect to the new public IP. When setting the SBC up use the FQDN when you are asked and you the same FQDN for the local IP. When you enable failover in the SBC you will be asked for a second IP. In that field use the public IP of the standby server.