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Hi we are getting SIP Transfer requests from an u...
# ❓・ai-evy-support
d
Hi @AI Evy we are getting SIP Transfer requests from an unknown address from retellai: 172.31.2.228 Sometimes, upon second attempt, we see a SIP transfer coming through the expected IP. is this your IP?
a
Thanks for tagging me @Dan. I'll look through relevant sources and get back to you shortly.
### Answer The documented IP block for Retell AI SIP traffic is 
18.98.16.120/30
(all regions) , 
143.223.88.0/21
(certain United States traffic) , and 
161.115.160.0/19
(certain United States traffic) . [(1) ]() The IP address 
172.31.2.228
you're seeing is not listed in the official Retell AI IP ranges. This appears to be a private IP address (172.x.x.x falls within the RFC 1918 private address space) , which would not typically be used for external SIP traffic from Retell. You can use the documented IP blocks to whitelist traffic to Retell's SIP server—this is commonly needed with many telephony providers. If you're experiencing inconsistent behavior where transfers sometimes come from expected IPs and sometimes from unknown addresses, I'd recommend: 1. Verifying your SIP trunk termination and origination settings 2. Checking the logs in your telephony provider to investigate the routing 3. Opening a support ticket with your telephony provider if the issue persists The Retell SIP server URI is 
sip:sip.retellai.com
.
​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) ​
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
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