The Option, get DNS "From ISP", only works when running SM/CPE as DHCP client for WAN interface instead of giving static IP. If in any case static IP address is the only option for WAN then ignore "From ISP" option for DNS under DHCP server tab of SM/CPE.
So, to utilize the option of "From ISP" do following.
- Go to Networking tab of SM/CPE
- Change WAN IP type to "DHCP"
- Then check the box "From ISP" under DHCP server tab of SM/CPE.