Classless Inter-Domain Routing
An IP address is interpreted as composed of two parts: a network-identifying prefix followed by a host identifier within that network. In the previous classful network architecture, IP address allocations were based on the bit boundaries of the four octets of an IP address. An address was considered to be the combination of an 8, 16, or 24-bit network prefix along with a 24, 16, or 8-bit host identifier respectively. Thus, the smallest allocation and routing block contained only 256 addresses—too small for most enterprises, and the next larger block contained addresses—too large to be used efficiently even by large organizations. This led to inefficiencies in address use as well as inefficiencies in routing, because it required a large number of allocated class-C networks with individual route announcements, being geographically dispersed with little opportunity for route aggregation.
IP traceback
Belenky and Ansari, outline a deterministic packet marking scheme. They describe a more realistic topology for the Internet – that is composed of LANs and ASs with a connective boundary – and attempt to put a single mark on inbound packets at the point of network ingress. Their idea is to put, with random probability of .5, the upper or lower half of the IP address of the ingress interface into the fragment id field of the packet, and then set a reserve bit indicating which portion of the address is contained in the fragment field. By using this approach they claim to be able to obtain 0 false positives with .99 probability after only 7 packets.