The adaptive firewall helps prevent entry to your computer by unauthorized users over your network connections. OS X Server uses an adaptive firewall that dynamically generates a firewall rule if a user or an IP address generates 10 consecutive failed login attempts.
Run these commands on the server as an admin user to enable the adaptive firewall.
For OS X Server on OS X Mavericks or Yosemite:
sudo pfctl -f /etc/pf.conf sudo /Applications/Server.app/Contents/ServerRoot/usr/sbin/serverctl enable service=com.apple.afctl sudo /Applications/Server.app/Contents/ServerRoot/usr/libexec/afctl -c sudo /Applications/Server.app/Contents/ServerRoot/usr/libexec/afctl -f
For OS X Server on OS X Mountain Lion or Lion:
sudo pfctl -f /etc/pf.conf sudo /Applications/Server.app/Contents/ServerRoot/usr/sbin/serverctl enable service=com.apple.afctl sudo /Applications/Server.app/Contents/ServerRoot/usr/libexec/afctl -f
Edit /System/Library/LaunchDaemons/com.apple.pfctl.plist so that pfctl(8) is invoked with the -e flag. This will automatically enable the packet filter the next time the server boots. This can be accomplished with these commands:
sudo defaults write /System/Library/LaunchDaemons/com.apple.pfctl ProgramArguments '(pfctl, -f, /etc/pf.conf, -e)' sudo chmod 644 /System/Library/LaunchDaemons/com.apple.pfctl.plist sudo plutil -convert xml1 /System/Library/LaunchDaemons/com.apple.pfctl.plist