Configure LAN and VPN for AT&T Wi-Fi calling

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 143
Ports 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 1500
MTU represents the maximum packet size that can be transmitted. Wi-Fi Calling performs best if the MTU is set to 1500.

Update equipment firmware
For 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