Of all the recommendations for securing a server, probably the most pervasive advice is to install some kind of packet filter between the server and any untrusted network. Many security strategies are based on the simple concept of reducing the attack surface. By using a packet filter to block or restrict network traffic, you can reduce the number of potential entry points that an attacker might take advantage of.
Packet filters usually come in the form of a firewall. A firewall can serve many purposes, but its primary function is to filter network packets and allow only traffic that matches specific predefined rules. However, a firewall isn't the only way to filter packets. Windows provides various built-in packet-filtering options to provide a primary or secondary layer of network protection.
Many organizations already protect crucial servers by implementing a firewall in a demilitarized zone (DMZ) between the server and the outside world. But sometimes you need additional packet-filtering capabilities on the server itself. For example, you might have a server hosted at a remote co-location facility that doesn't provide a firewall or any kind of packet filtering. In this case, it can be more convenient to use a packet filter on the server rather than install a separate firewall device. . . .
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