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NEC SL2100 PBX Configuration Question for ISP Failover

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Adam William

Systems Engineer
Aug 7, 2024
1
US
Hello all,

I have a question about a configuration scenario utilizing the SL2100, specifically failing over when 2 ISPs are present.

We have a dedicated on site PBX and 2 ISP connections with dedicated public IPs from each ISP.
The PBX has its own NAT IP address that changes if the ISP fails over, and this is where the problem seems to be for us. The VOIP carrier has 2 trunks setup for us to connect to, trunk IP 1 only accepts connections from ISP 1 public IP and trunk IP 2 only accepts connections from ISP 2 public IP.
The NATting is taking place on a firewall so the PBX has no way of knowing which public IP it's being translated to at the moment.

The easy solution here is to make the VOIP carrier accept traffic from both ISP IPs on the same trunk, but that will compromise redundancy from the VOIP carrier side of things as we are only connecting to one of their IPs/trunks.

Is there anything I can do on the PBX side of the config to make this failover happen?
Let's say the registration to Trunk IP 1 fails, is there a way for the PBX to try registering with different IPs until it's successful? Or any other solution that I could try?

The only configuration that seems to point to the VOIP provider IPs is under "10-23 : SIP System Interconnection Setup" the same primary VOIP IP is configured for options 1 to 10.
As a test I changed the second entry to point to the secondary VOIP IP and when dialing 92+phone number the traffic would go to the secondary IP which is what we want in a case of a ISP failover but the problem is that the number 2, not only routes the traffic in a specific way but also adds the number 2 to the phone number, so this only works if the number we are trying to call start with 2.

Any suggestion how I can make this work?
 
 https://files.engineering.com/getfile.aspx?folder=2099c2d9-8787-4a52-9d10-ac2579b76783&file=10-23_System.PNG
I am sure I tried this before and ended up having to use an SV9100.

Calum M
ACSS
 
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