13254: Dial->Sip: SIP URI DNS does not resolve or resolves to an non-public IP address

Twilio returns this warning when you use <Dial><Sip> with a SIP URI whose host does not resolve in public DNS or resolves to a private or otherwise non-public IP address. Use a valid SIP URI that points to a publicly reachable SIP endpoint.

• The domain in the SIP URI is missing, misspelled, or not published in public DNS.
• The DNS record for the SIP URI resolves to a private or internal IP address.
• The SIP endpoint is only reachable on an internal network and is not available through a public address.
• The SIP URI is invalid or the host portion of the URI is incorrect.

• Verify that the SIP URI is valid and that the host portion is correct.
• Check your DNS record and make sure the SIP URI resolves in public DNS.
• Update the DNS record so it resolves to a publicly routable IP address.
• Use a specific public IP address in the SIP URI if you do not want to use a domain.
• If your endpoint does not have a fixed public address, use SIP Registration so Twilio can route calls to the registered endpoint.

• TwiML <Sip>
• SIP Registration
• Use SIP with Twilio Voice