Hello,
Go to Network->Interfaces->Lan use the pen to edit it and set all the values there as listed: protocol Static, IPv4 address 172.16.1.1, netmask 255.255.255.0, let IPv4 gateway and IPv4 broadcast empty, and add your external DNS server here 8.8.8.8 but not 172.16.1.1.
Save&Apply when done.
Regards,