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want to know about 'Firewall Tunneling'I am in pro...
# ❓・ai-evy-support
d
@AI Evy want to know about 'Firewall Tunneling' I am in process of buying indian number from third party and later I'll connect it via SIP trunking
a
Thanks for tagging me @Developer. I'll look through relevant sources and get back to you shortly.
### Answer The available sources don't specifically cover "Firewall Tunneling" as a concept within Retell AI's documentation. However, here's what's documented regarding firewall configuration for SIP trunking: IP Whitelisting for Firewall Configuration When connecting via SIP trunking, you can whitelist Retell's IP blocks in your firewall to allow traffic to Retell's SIP server: [(1) ]() - 
18.98.16.120/30
(All regions) - 
143.223.88.0/21
(certain United States traffic) - 
161.115.160.0/19
(certain United States traffic) Transport Methods Supported Retell supports TCP (recommended) , UDP, and TLS transport methods. For different transport protocols on inbound calls, use these SIP server URLs: - TCP: 
sip:sip.retellai.com;transport=tcp
- UDP: 
sip:sip.retellai.com;transport=udp
- TLS: 
sip:sip.retellai.com;transport=tls
Media Encryption SRTP is supported (transport should be set to TLS to use SRTP) . If you're asking about a specific firewall tunneling technique or have connectivity issues with your third-party Indian number provider, could you clarify what specific challenge you're trying to solve? That would help me point you to more relevant guidance.
​ 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.
d
@AI Evy Hi team 👋 Thanks for the details. Just to confirm for an Indian DID provider form: Firewall tunneling = Static IP whitelisting only (no VPN), SIP ALG disabled, TCP preferred on sip.retellai.com, IPs: 18.98.16.120/30, 143.223.88.0/21, 161.115.160.0/19. Please confirm this is correct for inbound SIP trunking. Account: info@zoomintoweb.com
a
Thanks for the follow-up, @Developer. I'll get back to you soon.
### Answer Here's what I can confirm based on the documentation: IP Whitelisting The IP blocks you listed are correct for whitelisting traffic to Retell's SIP server: [(1) ]() - 
18.98.16.120/30
(All regions) - 
143.223.88.0/21
(certain United States traffic) - 
161.115.160.0/19
(certain United States traffic) Transport Method TCP is recommended. For inbound calls using TCP, the SIP server URL should be: 
sip:sip.retellai.com;transport=tcp
Origination Setup For inbound calls, you'll need to set Retell's SIP server address as the origination SIP URI: 
sip:sip.retellai.com
SIP ALG The documentation doesn't explicitly address SIP ALG settings. However, a community discussion mentions ensuring "SIP ALG is disabled" as part of firewall configuration for SIP trunking setups. [(2) ]() Note on Non-US Traffic The documentation states that some non-US traffic might come from IPs not listed above, but this was scheduled to be migrated to the first IP block (
18.98.16.120/30
) by 12/03/2025. [(1) ]() Since you're setting up an Indian number, you may want to confirm with your provider that this IP block is whitelisted. For account-specific questions, you can reach out via [Contact Sales]() .
​ To learn more, see the sources I considered: [[1] Custom Telephony Overview](https://docs.retellai.com/deploy/custom-telephony) [[2] Discord message from @jimmy_80670 on 2026-01-17](https://discord.com/channels/1186424376300679209/1186462578310910112/1462065812272709838) ​
Feel free to tag @AI Evy with additional questions. I also appreciate feedback, it helps me improve.
Thanks for the feedback, glad I was helpful.
d
@AI Evy hey the cumpany who provide us virtual number with SIP truncking, want to know that the retell AI servers are indian based server then they will provide number with SIP
a
Thanks for the follow-up, @Developer. I'll get back to you soon.
### Answer The available documentation does not specify whether Retell AI has India-based servers. [(1) ]() What the documentation does provide: - Retell's SIP server URI: 
sip:sip.retellai.com
- IP blocks for traffic whitelisting: - 
18.98.16.120/30
(All regions) - 
143.223.88.0/21
(certain United States traffic) - 
161.115.160.0/19
(certain United States traffic) The IP blocks listed indicate "All regions" for the first block and "certain United States traffic" for the others, but there's no explicit mention of India-specific server locations in the sources. For a definitive answer about server locations in India, I'd recommend reaching out directly to Retell AI: - [Contact Sales]() - [GitHub]() You can share the IP block information (
18.98.16.120/30
) with your Indian DID provider as the "All regions" block that handles traffic globally.
​ 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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