Allow Internet Protocol Security (IPSec)Internet Protocol Security is a method of encrypting traffic sent through the internet. It’s used to provide a secure voice and data communication path. Some routers permit IPSec messages to be blocked. AT&T Wi-Fi Calling requires IPSec pass-through to be allowed.
Open data ports 500, 4500, and 143Ports 500, 4500, and 143 (shown in the table) are used to communicate to the AT&T network and must be set to open.
Data ports
| Port | TCP or UDP | Service or protocol name | RFC | Service name |
| 500 | UDP | Wi-Fi Calling | 5996 | IKEv2 |
| 4500 | UDP | Wi-Fi Calling | 5996 | IKEv2 |
| 143 | TCP | Internet Message Access Protocol (IMAP) | 3501 | imap |
Set Maximum Transmission Unit (MTU) to 1500MTU represents the maximum packet size that can be transmitted. Wi-Fi Calling performs best if the MTU is set to 1500.
Update equipment firmwareFor best performance, always update modems, routers, and switches to the latest software/firmware versions available. Updates can typically be found on the equipment manufacturer’s website
Wi-Fi Calling Fully Qualified Domain Names (FQDN)A fully qualified domain name (FQDN) is the domain name for a computer, or other host equipment on the internet. Wi-Fi Calling should be able to traverse the following FQDNs:
- epdg.epc.att.net
- sentitlement2.mobile.att.net
- vvm.mobile.att.net