“Bogons is the name used to describe ip blocks not allocated by IANA and RIRs to ISPs and organizations plus all other ip blocks that are reserved for private or special use by RFCs (the actual term “bogons” comes from word “bogus”, as in bogus ip announcements).” These addresses are often used by “black hats” to conceal their actual addresses. This is one of the two primary bogon lists. The other is the Cymru list. Visit
The Team Cymru Bogon Reference Page for lots more info.
By the way the suggested best practice is to use BGP to deal with these rather than ACL’s.