Unless you have an internet routable block of 172.x.x.x your WAN and LAN IP address range appear to be reversed. (172.16.x.x – 172.31.x.x are in the private address space).
Configuring LAN connection (internal) is section 2.1
Set your internal IP block to a private IP address block.
Configuring WAN 3 is section 2.5 (You may be using WAN 1 or 2 but WAN 3 is the best match to the information provided.)
PPPoE is section 2.5.3 which matches your Encapsulation
MTU which may match your “BANDWIDTH” value.
I would confirm MTU == BANDWIDTH with your service provider.
You can read up on DNS, DHCP and other advanced features provided by your router.
You can download the manual from D-Link: DRO-250i+ Business Gateway
Private Address Space
The Internet Assigned Numbers Authority (IANA) has reserved the
following three blocks of the IP address space for private internets:
10.0.0.0 – 10.255.255.255 (10/8 prefix)
172.16.0.0 – 172.31.255.255 (172.16/12 prefix)
192.168.0.0 – 192.168.255.255 (192.168/16 prefix)