The D-Link DFL-210 is not a plug and play router. The router is not setup for DHCP, you must first assign a static IP address of 192.168.1.2 and a gateway of 192.168.1.1 on your PC's wired Ethernet adapter. To access the administration UI you connect via IE to 192.168.1.1. You should then check that you are running the latest firmware.
As of 9/8/06 version 2.05 was the newest available. You can download the latest from D-Link and use the tools/upgrade menu item. This is a straight forward process.
The default configuration comes with basic firewall rules that block all inbound traffic and allow outbound traffic via the 4 lan ports. The DMZ port is blocked. There are two elements to configure; the WAN interface, and DHCP.
The WAN interface under Interfaces/Ethernet/wan needed to be setup as a DHCP client for my Comcast connection by checking the Enable DHCP Client box. For every configuration change you then need to use the Configuration/Save and Activate menu item. I also found that the router should be up running before the Motorola cable modem is activated for the connection/address acquisition process to work.
If you have static DNS entries setup on your PC's Ethernet you should be able to access the Internet at this point. If you want to use DHCP to assign IP addresses and DNS entries on your network you need to setup a DHCP server. A default object called lannet is already setup for a pool of addresses (192.168.1.0 - 192.168.1.24) that you can use for DHCP. This object is also used in the lan to wan rule, with this rule the firewall only allows outbound traffic within this IP address range. I create a new object called DHCP_Pool since I have devices on my network with fixed IP addresses. Unfortunately the DHCP server does not have the ability to assign IP address based on MAC address, this is a major omission given that most sub $50 routers have this feature. I have an email out on the subject to D-Link support but no response yet.
The first configuration screen for DHCP.
The DHCP options tabs provides fields for specifying domain name, DNS and WINS entries. Since the router does not understand DNS, you must use an external DNS server (unless you run your own) such as the one gathered by the DHCP client on the wan interface. There are two default object, wan_dns1 and wan_dns2, that can be used to pass the external DNS servers to your clients.
This should get basic firewalled connectivity up and running. Next up; bandwidth management with pipes and pipe rules..