Hi,  @bad421 

Thank you for posting your on our business forum.

To better assist you with troubleshooting, we need some further clarification on your issue:

To confirm first: is the problem you encountered that the DNS proxy configured on your Post machine becomes unavailable when the AT&T router is operating? Could you also elaborate on the specific symptoms of the proxy issue on your Post machine?

Could you please help check the following items and provide relevant information for us:

• Have you tried running a test with only the AT&T router active, to check whether the Post machine works properly ?
• Have you attempted connecting your Post machine to the Comcast router to verify if it can work correctly in that setup?
• Would you be able to provide an overview of your current network topology?
• Do you use the ER707-M2 exclusively for automatic failover between WAN 1 and WAN 2? Are there any other additional configurations deployed on this device?

Thank you for your cooperation.