Class A network addresses have an 8-bit network-prefix with the highest order bit set to 0 and a seven-bit network number, followed by a 24-bit host-number. A maximum of 126 (27-2) /8 networks can be defined. 2 is subtracted because the /8 network 0.0.0.0 is reserved for use as the default route and the /8 network 127.0.0.0 has been reserved for the "loopback" function. Each /8 supports a maximum of 16,777,214 hosts per network. The host calculation requires that 2 is subtracted because the all-0s and all-1s host-numbers may not be assigned to individual hosts. Since the /8 address block contains 231 (2,147,483,648 ) individual addresses and the IPv4 address space contains a maximum of 232 (4,294,967,296) addresses, the /8 address space is 50% of the total ...view middle of the document...
Each Class C network address has a 24-bit network-prefix with the three highest order bits set to 1-1-0 and a 21-bit network number, followed by an 8-bit host number. Class C networks are now referred to as "/24s" since they have a 24-bit network-prefix. A maximum of 2,097,152 (221) /24 networks can be defined with up to 254 (28-2) hosts per network. Since the entire /24 address block contains 229 (536,870,912) addresses, it represents 12.5% (or 1/8th) of the total IPv4 unicast address space.
Class D addresses have their leading four-bits set to 1-1-1-0 and are used to support IP Multicasting (IP Address, 2010).
RFC 1918 IP address ranges
There are 3 IP ranges that are not routed across the Internet and can only be used on local networks. These are RFC 1918 IP addresses. You will sometimes see these used on ISP networks, where the devices can only be accessed from within the ISP's network, not from the rest of the Internet. There are 3 IP ranges defined in RFC 1918: 10.0.0.0/8 (10.0.0.0-10.255.255.255), 172.16.0.0/12 (172.16.0.0-172.31.255.255), 192.168.0.0/16 (192.168.0.0-192.168.255.255) (havoc, 2012)
Sampling of Martian/ Bogon address ranges
A bogon list is a compilation of address ranges that are used on private networks and should not be visible on the public Internet under normal operation. Some bogons do appear on the public Internet for various reasons, including the (legitimate) use of non-globally unique addresses for router interfaces, source address spoofing in DDoS attacks and the use of unallocated address blocks for malicious or fraudulent purposes (Hyan, 2004)
A Martian packet is a packet that is reserved for special use by (IANA) and can’t actually be used or delivered. They arise in denial of service attacks from ip spoofing (Baker, 1995).