I am currently implementing a workflow where I use the transfer_call function to hand off calls to an external phone number. This destination number connects to an IVR system that has strict security protocols.
The Issue: Our receiving IVR system identifies and authenticates incoming calls based on the Source IP address. Currently, because the calls from Retell seem to come from dynamic IPs, our IVR cannot consistently verify that the call is originating from your platform.
Could you please assist me with the following:
Static IP: Is there a way to configure a dedicated/static outbound IP address for my account or for specific phone numbers so we can whitelist it on our firewall?
IP Ranges: If a static IP is not possible, could you provide a documented list of all public IP ranges (CIDR blocks) used by Retell for outbound SIP/PSTN traffic? We need this to update our allowlist.
Any documentation or technical details regarding how your outbound media/signaling traffic is routed would be greatly appreciated.
Based on my research and the information sources, I can confirm that Retell AI provides documented IP ranges you can whitelist for your IVR system.(1)(2)
IP Ranges for Whitelisting:
Retell provides the following IP blocks for traffic:(1)
143.223.88.0/21 (certain United States traffic)(1)
161.115.160.0/19 (certain United States traffic)(1)
You can use these IP blocks to whitelist traffic to Retell’s SIP server.(1) For your use case with call transfers, these are the IP ranges your IVR system should whitelist to authenticate incoming calls from Retell.(2)
Supported transport methods: TCP (Recommended), UDP, TLS(1)
Static IP for U.S. Calls:
Static IP addresses are available for U.S. calls, giving you complete control over your telephony setup.(3) This feature is particularly useful for enterprise integrations and custom call routing.(3)
For call transfer functionality specifically, the documented IP ranges should allow your IVR to identify and authenticate calls originating from Retell’s platform.(2)