D-Link DI-604 as router/firewall only ?

If you can get a Fixed (or any) IP without having to do a PPOE connection, then the Router will also let you setup a Fixed IP on the WAN port - then the internal LAN side can NAT through the router using that public IP.

You can set the DSL modem in bridge mode so you can use the D-links's routing/firewall. Since your DSL modem is in dumb mode, you will have to use the D-link to connect to your provider though, not what you really wish.

normally, one would intentionally use the NAT feature + DHCP to use a private address to your network. I like to map the MAC address to a specific IP which basically makes the DHCP act like a static address, but this is not a requirement. BTW: the router will not make a connection to your ISP. That's done by the DSL modem. The router makes that connection available (ie shared) by anything plugged into it).

(remove No-Spam to reply)

Yes, use a static IP or even a dynamic IP on the WAN interface of the Dlink. Assuming I guess that your modem is already doing NAT for you, which is common enough these days..

Little is gained by this setup except for advanced featurs of the 604 -- which were laughable last time I looked at one, but I imagine better firmwares have come out in the meantime. I'm sure you have your reasons.

Note that to expose an external port you'll need to configure the router in the modem as well as the D-Link.

-Russ.