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I am trying to register an Inbound SIP Trunk from ...
# ❓・ai-evy-support
g
@AI Evy I am trying to register an Inbound SIP Trunk from a Brazilian provider (VoIP do Brasil) using the domain voipdobrasil1.net.br. While my credentials are correct and work on a local softphone, Retell fails to register and incoming calls to my number (+55 27 2018-0991) result in 'out of service' messages. Does Retell AI have any known compatibility issues or regional blocks regarding Brazilian SIP providers or phone numbers? Also, please provide your static outbound IP addresses so I can ask my provider to whitelist them, as they might be blocking international registration attempts from your servers by default.
a
Thanks for tagging me @Guilherme Z.. I'll look through relevant sources and get back to you shortly.
configuration, check your provider's logs for error messages [(1) ]() . **
​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] Twilio](https://docs.retellai.com/deploy/twilio) [[3] Import Phone Number](https://docs.retellai.com/api-references/import-phone-number) [[4] SIP Trunk Outbound Call - No SIP INVITE reaching my server](https://community.retellai.com/t/sip-trunk-outbound-call-no-sip-invite-reaching-my-server/760) ​
### Answer Retell AI does not use static IP addresses for SIP registration [(1) ]() . Currently, Retell's SIP server does not have a static IP [(2) ]() . Instead, you can use the IP block 
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) to whitelist traffic to Retell's SIP server [(1) ]() . For your Brazilian SIP trunk setup with VoIP do Brasil, Retell AI supports custom telephony integration through Elastic SIP Trunking, which is the recommended method . You'll need to: 1. Set up elastic SIP trunking with your provider and configure your number to point to it 2. Configure the origination (inbound) setting to point to Retell's SIP server address: 
sip:sip.retellai.com
3. Import your Brazilian number (+55 27 2018-0991) to Retell in E.164 format: 
"+552720180991"
[(3) ]() For transport methods, Retell supports TCP (Recommended) , UDP, and TLS [(1) ]() . For inbound calls using TCP, the SIP server URL needs to be 
sip:sip.retellai.com;transport=tcp
. Regarding your "out of service" issue, check your origination setting in your SIP trunking provider and review the logs in your telephony provider . The documentation doesn't mention any specific regional blocks for Brazilian providers or numbers. Ask your provider (VoIP do Brasil) to whitelist the IP blocks mentioned above: 
18.98.16.120/30
, 
143.223.88.0/21
, and 
161.115.160.0/19
[(1) ]() [(4) ]() . If issues persist after proper
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
g
@AI Evy My provider (VoIP do Brasil) confirmed they don't have any IP blocks on their side. However, they require me to whitelist their server IP in my Retell configuration to allow the SIP registration to complete. Provider's SIP Server IP: 177.11.50.202 Can you please ensure this IP is whitelisted for my account's SIP Trunk, or let me know if I should add it to a specific field in the dashboard (like 'Authorized IPs' or 'SBC IP') to fix the 'out of service' issue for my number +552720180991?
a
Thanks for the follow-up, @Guilherme Z.. I'll get back to you soon.
### Answer Retell AI does not provide a user-accessible interface to whitelist your provider's IP addresses in your account configuration [(1) ]() . The IP whitelisting works in the opposite direction - you need to whitelist Retell's IP blocks on your provider's side, not whitelist your provider's IPs on Retell's side . For elastic SIP trunking integration, when you import your number to Retell, you provide the termination SIP URI (which is your provider's server address for outbound calls) in the import configuration [(2) ]() [(1) ]() [(3) ]() . This is how Retell knows where to send outbound traffic. For your setup with VoIP do Brasil: 1. **Termination SIP URI**: When importing your number (+552720180991) to Retell, you should provide your provider's termination URI. Based on the IP you mentioned (177.11.50.202) , this would likely be formatted as 
sip:177.11.50.202:5060
or the FQDN equivalent if your provider uses one [(1) ]() [(4) ]() . 2. **Origination (Inbound) **: Your provider needs to route inbound calls to Retell's SIP server: 
sip:sip.retellai.com
[(1) ]() . 3. **Authentication**: If your provider requires authentication credentials, you'll need to supply the username and password when importing the number to Retell [(2) ]() [(3) ]() . There is no "Authorized IPs" or "SBC IP" field in Retell's dashboard for whitelisting your provider's IPs. The configuration happens through the termination URI you provide
during number import [(1) ]() [(5) ]() . If you haven't already imported your number, you can do so via the dashboard or programmatically using the Import Number API . Make sure to use E.164 format: 
+552720180991
[(4) ]() . Check out these potentially useful sources: [Custom Telephony Overview]() , [Import Phone Number API]()
​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] Twilio](https://docs.retellai.com/deploy/twilio) [[3] Telnyx](https://docs.retellai.com/deploy/telnyx) [[4] SIP Trunk Outbound Call - No SIP INVITE reaching my server](https://community.retellai.com/t/sip-trunk-outbound-call-no-sip-invite-reaching-my-server/760) [[5] AI in SIP Calling & Telephony Solutions | Retell AI](https://www.retellai.com/blog/integrating-ai-with-sip-trunking-and-modern-telephony) ​
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
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