ICX7150 Lennar Home AT&T Fiber what is the difference between configuring ICX as a Switch vs a Route

[dariusz_basiaga]

My AT&T Fiber comes with a DEMOX router that also includes Wi-Fi.  However, I do not want the AT&T Router to do anything besides translate light into electrons and feed my ICX7150.  I want the ICX7150 to perform DHCP assignment and DNS assignment.  I do not want to be forced to AT&T DNS (they prevent you from changing the DNS to reduce tech support calls).

Initially the ICX7150 was set up by the previous owner, and it was running very old firmware, I think from 2017.  So I upgraded the firmware, but I forgot to note which firmware was on the switch (was it S or R I don't' know).  I have loaded S (switch) but now I lost my AT&T internet.  I have also reset the AT&T router to the defaults since I wanted to start from scratch. 

The Wi-Fi and internet provided by the AT&T router works fine, it's the ICX directed Wi-Fi that is no longer routing and neither is the ICX.

I have set the ICX to static IP and that IP, and Gateway are on the same IP network and subnet as the AT&T router, mainly the 192.168.1.x range.

The gateway of ICX is pointing to the AT&T Gateway IP.

So should I switch ICX to routing, and what exactly do we lose between ICX acting as a switch vs a router?