This is really great advice. Servers should implement a policy of default deny wherever possible. While it might not block the attacks directly, but it can sign

This is really great advice. Servers should implement a policy of default deny wherever possible. While it might not block the attacks directly, but it can significantly inhibit the attacker's ability to quickly pivot to a useful pwned box. For example, most scripted attacks leverage an exploit, then immediately download a payload, execute, and phone home to "register" the box on the attacker's network of owned machines. Having a solid set of firewall rules based on a base policy of default deny will stop these scripted attacks, which constitutes the vast majority of the attacks you'll see knocking on your door in the wild.