Public IP changes

• What If he has AT&T Fiber Internet or an AT&T Internet that is based on some form of DSL?

Thanks for the comment 

@JefferMC  Can you share some kind of picture or something?

The gateway for Fixed Wireless Internet can also be used with Fiber and DSL, and there are multiple wired gateways, so no one picture will solve this.  

If the user can find a model number on the Gateway, that will help (unless it's the 5268AC, described above).  If the device doesn't have any connections other than Power, then it must not be wired.

If the service requires a mounted antenna with wiring to the gateway (5268) then has ATT Fixed Wireless cellular tower primary offered in selected areas of 18 states that are rural to semi rural. This service uses 4G LTE band 30 and has been offered for past 5+ years.

If the gateway is egg shaped, no antenna or wiring to the gateway then has the newer (less than 1 year) ATT AIR which is Fixed Wireless Access being offered in several markets including urban and suburban besides rural. 

Both services are cellular tower services using CGNAT where an upstream device has the public IP address and the end user receives a private IP address from a pool of addresses maintained by the upstream device. Additional the upstream device can change which means geo location can change for the private IP address. Other FWA providers using similar CGNAT include T-Mobile, Verizon and US Cellular.

EDIT, your usage of ISB has me confused… the only ATT product that I am aware of using that term is the UVERSE IPTV receivers made by CISCO includes the DVR ISB 7500 and non DVR receiver ISB 7000. 

@JefferMC @my thoughts  Thanks both to sharing your experience.