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IP address

The IP address is a 32-bitaddress consisting of an address part for the network identifier (net-id) and the user part for the host identifier

(host-id). The first bits define the network class. The network part can be between 7 bits and 21 bits long, depending on the network class, and is used for the network identifier (netid). The user part is used for the host identifier and can be between 8 bits and 24 bits long. Originally, the IP address consisted of 8 bits for


addressand 24 bits for the subscriber address. As a result, only 256 networks could be addressed. Therefore, RFC 791 divided the addressing space into three and later into five different classes, which are designated by the letters A, B, C, D, and E. Classes A, B and C are distinguished by the different lengths of the network and user identification fields, while class D is reserved for IP multicast. In addition, the addressing specifications for the various classes differ from one another. IP addresses are written in dotted decimal notation, which is converted into domain names in the DNS system

IP address classes

IP address classes

ClassA address: Address class A is suitable for users who have few networks and many computers. It is characterized by the most significant bit (MSB), which is a "0". This means that the addresses are in the range from to The network indicator (net-id) is encoded by 8 bits (with prefix

) or 7 bits, which results in 128 different networks. The number of possible IP addresses within a network results from the 24 bits, which corresponds to 16,777,216. For this reason, these addresses are only assigned to particularly large usersClass B address: Address class B is interesting for users with a medium distribution of networks and computers. Class B addresses are identified by the two-bit combination "10". The address range extends from to The network ID is 16 or 14 bits long, which corresponds to a theoretical network number of 16,384 networks. The number of possible nodes

within a network is 65,534 with 16 bitsClass C address: Address class C is suitable for companies with many networks and few computers. It is identified by the prefix 110. Addresses of this class lie in the range from to The 24 or 21 bit network identification theoretically enables the unique identification of 2,097,152 different networks with 256 nodes each. This class is especially interesting for small companies. Addresses of this category

are no longer assigned due to address scarcityClass D address: The identification

for IP addresses of class D is the bit combination 1110. The address range goes from to Due to the 28 bit long identifier for the multicast groups, the formation of up to 268,435,456 groups is possibleClass E address: Class E identifier is the presented bit combination 11110 in the five highest order

bits. Class E addresses are reserved addresses for future applications. The address range is from to Internet address identifies a computer on the network. Computers with multiple physical ports

have multiple addresses. An address with the number 0 identifies a network. Addresses in which every bit is set to "1" are reserved for broadcast messages

IP addresses in decimal notation

Changing the location of a computer has a disadvantage with this scheme, since the computer's Internet address changes from one network to another. The notation of Internet addresses is generally such that each byte is represented as a decimal number and is separated from the neighboring byte by a period (e.g. Each network connected to the Internet

is thus assigned a specific network identifier (net-id); the associated user identifiers can be assigned by the local network operator itself.

IP addresses for private networks

IP addresses for private networks

The decimal notation shown here, in which the individual address blocks are separated by dots, is called Dotted Decimal Notation. Since these numeric Internet addresses are not informative with regard to the location and are also difficult to remember, it has been agreed to use hierarchical alphanumeric Internet names for the address representation. These addresses then look as follows: "" or "". The Internet names are directly related to the Internet address. The conversion from one to the other and vice versa can be done via host tables or via worldwide valid DNS servers. Theaddress structures are described in RFCs 1597, 1814 and 1918, with RFC 1918 specifying the address ranges reserved by IANA

for private networks.Since the classic IP addressing system was relatively static and many millions of addresses were given away in the given addressing options, the IP classes were replaced by Classless Interdomain Routing (CIDR) as early as 1993. This method is used in IPv4 addressing and IPv6 addressing

. IP addresses that are assigned when devices are configured and do not change are called static IP addresses. Dynamic IP addresses, on the other hand, are those that are assigned dynamically using Dynamic Host Configuration Protocol (DHCP).

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Englisch: IP address
Updated at: 10.09.2015
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