Comcast bridge mode issues
Here's the scenario: Client uses Comcast and has the Comcast Business modem/router (I won't call it the gateway here to avoid confusion) . I put it in bridge mode and configured the public static IP address on the public side of a Sonicwall TZ400 (X1) and set up DHCP for a private subnet and forwarded a port to a test machine inside. When I do that I get nothing, in or out. I suspect that it is the Comcast gateway address. Before putting the comcast router in bridge I did note what they said was the gateway address but it doesn't seem to work.
My question is, is there a way to verify what the comcast gateway address is supposed to be for a specific public IP?. Should the last v4 octet be 1 more or less than the public static address, as I have seen before, or could it be most anything? I hate Comcast and their AI gatekeeper. Can't get through to anyone other than script-readers and only then after three or four tries to get to a human at all. Thanks in advance.