RFC 3330 instead of RFC 1918

Many people have implemented RFC 1918 to block private addresses. Actually there are other range of IP addresses that you need to block according to RFC 3330.

   Address Block             Present Use                       Reference
 ---------------------------------------------------------------------
 0.0.0.0/8            "This" Network                 [RFC1700, page 4]
 10.0.0.0/8           Private-Use Networks                   [RFC1918]
 14.0.0.0/8           Public-Data Networks         [RFC1700, page 181]
 24.0.0.0/8           Cable Television Networks                    --
 39.0.0.0/8           Reserved but subject
                         to allocation                       [RFC1797]
 127.0.0.0/8          Loopback                       [RFC1700, page 5]
 128.0.0.0/16         Reserved but subject
                         to allocation                             --
 169.254.0.0/16       Link Local                                   --
 172.16.0.0/12        Private-Use Networks                   [RFC1918]
 191.255.0.0/16       Reserved but subject
                         to allocation                             --
 192.0.0.0/24         Reserved but subject
                         to allocation                             --
 192.0.2.0/24         Test-Net
 192.88.99.0/24       6to4 Relay Anycast                     [RFC3068]
 192.168.0.0/16       Private-Use Networks                   [RFC1918]
 198.18.0.0/15        Network Interconnect
                         Device Benchmark Testing            [RFC2544]
 223.255.255.0/24     Reserved but subject
                         to allocation                             --
 224.0.0.0/4          Multicast                              [RFC3171]
 240.0.0.0/4          Reserved for Future Use        [RFC1700, page 4]

All incoming packets with source IP address of these address blocks facing to your internet gateway you need to filter it.