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.
Anonymous blog
An IP address is a unique numerical label assigned to a computer connected to a computer network that uses the Internet Protocol for communication. The most popular implementation of the Internet Protocol would be the Internet (capitalized, to differentiate it from smaller internetworks). Internet Service Providers (ISPs) are allocated chunks of IP addresses by a Regional Internet registry, which they then assign to customers. However, ISPs do not have enough addresses to give the customers their own address. Instead, DHCP is used; a customer's device (typically a modem or router) is assigned an IP address from a pool of available addresses. It keeps that address for a certain amount of time (e.g., two weeks). If the device is still active at the end of the lease, it can renew its connection and keep the same IP address. Otherwise, the IP address is collected and added to the pool to be redistributed. Thus, IP addresses provide regional information (through Regional Internet registries) and, if the ISP has logs, specific customer information. While this does not prove that a specific person was the originator of a blog post (it could have been someone else using that customer's Internet, after all), it provides powerful circumstantial evidence.