Twilio makes HTTP requests to your server to fetch your app's TwiML instructions. Some users prefer to know which IP address the request from Twilio is coming from in order to open up specific ports in a firewall. However, due to the fluid nature of our cloud architecture, we don't have a set range of IPs that requests are sent from or know in advance what they will be.
Because Twilio's requests will be coming from different IP addresses, we instead recommend that you validate that a request came from Twilio by other means. Please see our documentation on securing your application for more details.
If the inability to have a request come from a static IP address is a serious concern for your enterprise, please contact our sales department to discuss your security needs and other options which might be available.
Notice: Twilio will be expanding our media IP Pool in Fall of 2019. Elastic SIP, SIP Interface, Client, and Mobile Voice customers will want to take action now to avoid service disruption. For full details, please see Notice: Twilio SIP and Client Voice Media IP Pool Expansion (September 2019).
See also: All About Twilio IP Addresses