Changing IP address of connections from AWS towards SIP

[netoob]

Hello all,

We have installed a PBX on AWS and connected it to our on-prem Router via VPN.
My on-prem router is connected to the SIP provider via another on-prem MUX device.

All connections are working fine, EXCEPT, my SIP provider has a condition that all connections to their server must originate from a specific IP that they have assigned to us.

Since AWS machine is connected via VPN, all calls from PBX are picking up the IP of the AWS machine.

For resolving this, i need to change the IPs of all connections from AWS to SIP.
Someone suggested i need NAT loopback/reflection for this.

Please guide how can this be done?

Regards.