Are you sure the DNS settings are configured in your DHCP server?
On a windows client use this to see all the ip parameters that the client has from the DHCP server.
ipconfig /all
Configure the DNS server settings in DHCP here.
Web
Network - DHCP - Edit on interface
DNS 1
Advanced - DNS 2
CLI
set interface bgroup0 dhcp server option dns1 1.1.1.1
set interface bgroup0 dhcp server option dns2 2.2.2.2