Tweet
RFC 2827 recommends that ISPs police their customers' traffic by dropping traffic entering their networks that is coming from a source address not legitimately in use by the customer network. The filtering includes but is in no way limited to the traffic whose source address is a so-called "Martian Address" - an address that is reserved, including any address within 0.0.0.0/8, 10.0.0.0/8, 127.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16, 224.0.0.0/4, or 240.0.0.0/4.
Note that RFC 3704 updates RFC 2827.
Source: https://www.ietf.org/rfc/rfc3704.txt