Hello tamuno,
Firewalls can block unnecessary traffic, based on the Layer 4 parameters, TCP / UDP ports, IP address etc.. This device, I can say, blocks around 70 % of the unwanted traffic.. firewalls have basic IPS functionality on the software which is very limited on the total signatures (around 20)...
If you are talking about full-fledged security, firewalls cant really do it 9as told above)... simple example is, if there is a mail server, the firewall will permit port 25/110 into the inside network, just by seeing the layer 4 header... wht if the attacker does a port sweep, finds that the firewall has 25/110 open, and introduce vulnerabilities on these open ports?? your network is vulnerable to attacks !!!! IPS will be the DEVICE here, which can inspect packets on layer 7 (application layer) and see if the packets entering the network is allowed/denied.. combining firewall & IPS, network administrators can get 95% of unwanted traffic blocked..
Hope this helps.. all the best.. rate replies if found useful..
Raj
