No way to disable this on their side. If they updated to IPV6 its is there to stay.

Instead of server why didn't you just create loop back rules ?

Comcast Modem Ip Default

SMCD3GNV Wireless Cable Modem Gateway User Manual Preface The SMCD3GNV3 Wireless Cable Modem Gateway is the ideal all-in-one wired and wireless solution for the home or business environment. SMC is proud to provide you with a powerful, yet simple communication device for connecting your local-area network (LAN) to the Internet. Jul 17, 2019 The Cisco DPC3941B Comcast Gateway is a Business Wireless Gateway often given to Comcast Business customers for their Internet service. This equipment, by itself, is not recommended for use with VoIP service. Common issues include one-way audio, dropped calls, failed transfers and deregistrations, among others.

Comcast Modem Access Ip

I can guess some of your behavior.

1. You are getting spoof warning ?

If you are getting spoof warning turn on IPV6 on the device the mobile devices are trying to connect to. Here is the skinny. You see this mainly with IPAd and Iphones with data connecting to both the wireless wlan and the provider. It is a symptom of dual homing one being a IPv4 and ones being IPv6. So try enableing IPv6 on the item these devices are trying to connect to.