My network need additional security. I replaced the previous firewall with the PIX 515E. Connecting it to the (DLINK DSL-G604T)router, there is no communication. How can i solve the problem
What level of comunication issue you have? Is it due to cabling issue (straight vs cross-over UTP) or configuration?
Make sure you use cross-over utp. If this is already in place, make sure both router and pix interface is in unshut/active mode. Other than that, check the IP asigned for the router and PIX interfaces + netmask. Other than that, maybe you need to allow icmp from router to reach pix outside interface (or any interface you connect to router).
On the PIX end, is the LED blinking/on when you connect to the DLINK router?