Outbound calls fail when whitelisting IP address block

Support Help
1

set up SIP trunking for outbound calls through SignalWire and whitelisted IP block 18.98.16.120/30. We’re getting “The number you have dialed is not configured correctly” errors. I also tried calling the Retell endpoint with :5061;transport=tls and :5060;transport=tcp but both failed. SignalWire logs show 486 Rejected SIP code from Retell’s servers. Here is an example Call_ID call_10fafca142a0b585e0129338574

When I disable the whitelisting protection on SignalWire side the calls go through fine. Can you confirm if I need to add other IP addresse blocks besides 18.98.16.120/30 or what else might fix this? We’re only calling US/Canada regions.

Thank you

Support for Indian Server IPs and Whitelisting for TeleCMI Integration
2

Based on the Retell AI documentation, you need to whitelist additional IP blocks beyond just 18.98.16.120/30(1).

For US/Canada regions specifically, you should whitelist these IP blocks(1):

  • 18.98.16.120/30 (All regions)
  • 143.223.88.0/21 (United States only)
  • 161.115.160.0/19 (United States only)

The documentation notes that “Some non US traffic might go from IPs not listed above, but will be migrated to the first IP block by 12/03/2025”(1).

Since you’re only calling US/Canada regions and your calls work when whitelisting is disabled, the issue is likely that SignalWire is blocking traffic from the US-specific IP blocks (143.223.88.0/21 and 161.115.160.0/19) that aren’t currently whitelisted(1).

For transport methods, Retell supports UDP, TCP, and TLS(1). The documentation shows the SIP server URL formats as(1):

  • For UDP: sip:sip.retellai.com;transport=udp
  • For TCP: sip:sip.retellai.com;transport=tcp
  • For TLS: sip:5t4n6j0wnrl.sip.livekit.cloud;transport=tls

Add all three US IP blocks to your SignalWire whitelist and this should resolve the 486 Rejected errors you’re seeing.

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