AT&T Wi-Fi Calling LAN and VPN configuration

To use AT&T Wi-Fi Calling, your device must be able to communicate with the AT&T network. In some cases in order to communicate effectively you may need to change your router settings. If you have a simple router configuration that has not been customized, you may not have to make any changes to your settings.  

If the router’s configuration has been updated or you’re using a firewall you may have to update the router setting to support AT&T Wi-Fi Calling.

LAN configurations to support AT&T Wi-Fi Calling
For assistance in updating the configurations below refer to the router manufacturer's website or contact your Internet Service Provider.

Internet Protocol Security (IPSec) must be allowed
Internet Protocol Security is a method of encrypting traffic sent through the Internet. It is 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.

Data ports must be open
Routers can be set to block traffic using certain ports. Ports 500, 4500, and 143 as shown in the table below are used to communicate to the AT&T network and must be open. Port blocking is sometimes implemented in the form of access lists.

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

Maximum Transmission Unit (MTU)
The MTU represents the maximum packet size that can be transmitted. Wi-Fi Calling performs best if the parameter is set to 1500. 

Network equipment software (firmware)
For best performance always use the latest software version on the following equipment:

• Modems
  
• Routers
  
• Switches
  

Refer to the manufacturer’s website to download the latest software version.

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