Classful network
Power classes is a term that has been used in connection with the Internet Protocol.
Net classes (often called by the English term classful network) were a subdivision used from 1981 to 1993 of the IPv4 address range into subnets for different users. From the network class, the size of a system could be derived. This is during the routing in the Internet is important to distinguish whether a destination IP address in its own or a foreign network can be found. Since net classes have proved to be too inflexible and not very economical in use of the scarce resource IP addresses, they were 1985, initially by subnetting and 1992 supplemented with Supernetting and 1993 finally with the introduction of Classless Inter- Domain Routing (short: ' CIDR ' ) replaced. Nevertheless, the outdated and no longer relevant in practice the concept of network classes is often still taught by faculty and is frequently continue in textbooks.
Concept of network classes
The concept of IP addresses used initially only provided a rigid division. These 8 bits for addressing the network were provided, the remaining 24 bits addressed a specific subscriber of the network. In this concept, but only 256 networks were possible. This was recognized as too little. Therefore, in September 1981, the so-called net classes were introduced by RFC 791, the redesigned this division.
About the net classes of the entire address space in first three (later five) net classes was divided. All subnets of a network class in this case had the same standard size. The grid sizes of the classes were very different, so in a Class C network only 254 hosts were possible, whereas were made possible with a Class A network over 16 million hosts. This should make it possible to assign individual organizations and organizations of large networks as needed. But led the rigid grid sizes too big waste because, for example a user with 100,000 hosts a Class A network had to be assigned. Of these, however, were only a total of 126 available and in this particular case, over 16 million IP addresses would have been wasted. Therefore, the IP classes were replaced in 1993 by RFC 1518 and RFC 1519 by the Classless Inter-Domain Routing. With CIDR, networks will be awarded in flexible sizes within the entire address space, hence a derivation of the network size of the IP address is no longer possible.
The network class was determined by the first bits of the binary IP address. The classes D and E region assigned had been reserved in the original specification for an extended addressing. This was later divided into the classes D and E, where the address range of Class D is further used even after the abolition of the net classes for multicast applications. The address range of the former class E is still reserved.
Overview of network classes
Outdated teaching
Often, however, this doctrine of the net classes will only lead to confusion, since it is obsolete with the introduction of CIDR. Today, it has almost no practical relevance more importance, since the size of a network is no longer derive only from the IP address, but is mandatory to specify a network mask is required. The technology behind it is called VLSM.
Even today, however, are some implementations the old network class concept: The Point - to-Point Protocol mechanism under Windows ( CE, XP ) manages the size of the network from the case of direct connection of two PCs from the IP address, enter a subnet mask is not provided. Remaining practical significance for the network class even with the use of historical routing protocols such as RIPv1. Because these older, but still occasionally used in LANs routing protocols do not transmit subnet mask that belongs to the network class of the IP address subnet mask is automatically accepted if necessary. Similarly, IP implementations behave in historical operating systems that were not developed any further since the standardization of subnetting 1985. The historical net classes are also the light of the reserved address space for private IP addresses.
The vanishing importance of network classes is also reflected in the IP assignment policy of the Regional Internet Registries (RIR ) resist, as found in the previous class -C region also allotments that go far beyond the size of the network of the old class C ( the associated mechanism is supernetting ). Are now assigned due to a shortage of IP addresses, the former Class A areas in smaller blocks analog, such as the former class A network number 80 taken from the range 80.128.0.0 to 80,159,255,255 to the German Telekom AG.
An overview of current and contracts awarded in the past, network sizes in the RIPE region can be found in the document RIPE -345 on the sides of the RIPE NCC.