efix. A maximum of 2097 152/24 networks can be defined with up to 254 hosts per network. Other Classes In addition to the three most popular classes, there are two additional classes. Class D addresses have their leading four bits set to 1-1-1-0 and are used to support IP multicasting. Class E addresses have their leading four bits set to 1-1-1-1 and are reserved for experimental use. 4.9.2 Dotted-Decimal Notation To make Internet addresses easier for human users to read and write, IP addresses are often expressed as four decimal numbers, each separated by a dot. This format is called 'dotted-decimal notation.' Dotted- decimal notation divides the 32-bit Internet address into four 8-bit (byte) fields and specifies the value of each field independently as a decimal number with the fields separated by dots. Below is shown how a typical /16 (class B) Internet address can be expressed in dotted decimal notation: 10010001000010100010001000000011 145.10.34.3 The dotted-decimal values shown below indicate how, each of the three principle classes can be assigned, where the administrator assigns Xxxx values to the hosts: Class A: 1.xxx.xxx.xxx to 126.xxx.xxx.xxx Class B: 128.0.xxx.xxx to 191.255.xxx.xxx Class C: 192.0.0.xxx to 223.255.255.xxx This is knwon as classful addressing and has several inherent limitations. A /16 network consists of 65 536 nodes while a /24 network can have only 256 nodes. Most of the medium sized organisations have requirements somewhere in between. Such organisations were allotted one /16 network. Hence /16 networks have now become scarce. Multiple /24 subnets are now allocated to an organisation that has greater than 256 nodes, but this results in a new problem of growing sizes of Internet routing tables, increasing processing capacity requirements for routers and hence increasing cost. Classless addressing, in which there is more flexibility in subnetting, takes care of this wastage in present and future networks but past mistakes cannot be corrected. When the Internet was designed the develo