Internet Protocol Address

Internet Protocol Address : An Internet Protocol (IP) address is a number which assigned to each device connected to a computer network that uses the Internet Protocol for communication.

Two types of IP version mainly use one is IP version 4 or (IPv4) and IP version 6 or (IPv6).

Internet Protocol Version 4 : Internet Protocol version 4 (IPv4) is the fourth version in the development of the Internet Protocol (IP) and the first version of the protocol to be widely deployed. IPv4 is described in IETF publication RFC 791 (September 1981), replacing an earlier definition (RFC 760, January 1980).

An IP address in IPv4 is 32-bits in size, which limits the address space to 4294967296 (2³²) IP addresses.IPv4 addresses are usually represented in dot-decimal notation, consisting of four decimal numbers, each ranging from 0 to 255, separated by dots, e.g., 172.16.254.1. Each part represents a group of 8 bits (octet) of the address.

The first octet referred here is the left most of all. The octets numbered as follows depicting dotted decimal notation of IP Address:

The number of networks and the number of hosts per class can be derived by this formula:

When calculating hosts' IP addresses, 2 IP addresses are decreased because they cannot be assigned to hosts, i.e. the first IP of a network is network number and the last IP is reserved for Broadcast IP.

Class A Address

                                                         The first bit of the first octet is always set to 0 (zero). Thus the first octet ranges from 1 – 127, i.e.Class A addresses only include IP starting from 1.x.x.x to 126.x.x.x only. The IP range 127.x.x.x is reserved for loopback IP addresses.The default subnet mask for Class A IP address is 255.0.0.0 which implies that Class A addressing can have 126 networks (2⁷-2) and 16777214 hosts (2²⁴-2).Class A IP address format is N.H.H.H.

Class B Address

                                    An IP address which belongs to Class B IP Addresses range from 128.0.x.x to 191.255.x.x. The default subnet mask for Class B is 255.255.x.x. Class B has 16384 (2¹⁴) Network addresses and 65534 (2¹⁶-2) Host addresses. Class B IP address format is N.N.H.H.

Class C Address

                                    The first octet of Class C IP addresses range from 192.0.0.x to 223.255.255.x. The default subnet mask for Class C is 255.255.255.x. Class C gives 2097152 (2²¹) Network addresses and 254 (2⁸-2) Host addresses.Class C IP address format is: N.N.N.H.

Class D Address

                                     Very first four bits of the first octet in Class D has IP address rage from 224.0.0.0 to 239.255.255.255. Class D is reserved for Multicasting. In multicasting data is not destined for a particular host, that is why there is no need to extract host address from the IP address, and Class D does not have any subnet mask.

Class E Address

                                    This IP Class is reserved for experimental purposes only for R&D or Study. IP addresses in this class ranges from 240.0.0.0 to 255.255.255.254. Like Class D, this class too is not equipped with any subnet mask.

Internet Protocol Version 6 : In IPv6, the address size was increased from 32 bits in IPv4 to 128 bits or 16 octets, thus providing up to 2¹²⁸ (approximately 3.403×10³⁸) addresses. This is deemed sufficient for the foreseeable future.

Address Structure

                                                                                                                                                  An IPv6 address is made of 128 bits divided into eight 16-bits blocks. Each block is then converted into 4-digit Hexadecimal numbers separated by colon symbols.
For example, given below is a 128 bit IPv6 address represented in binary format and divided into eight 16-bits blocks:

0010000000000001 0000000000000000 0011001000111000 1101111111100001 0000000001100011 0000000000000000 0000000000000000 1111111011111011

Each block is then converted into Hexadecimal and separated by ‘:’ symbol:

2001:0000:3238:DFE1:0063:0000:0000:FEFB

Even after converting into Hexadecimal format, IPv6 address remains long.

Global Unicast Address

                                                                                                                                               This address type is equivalent to IPv4’s public address. Global Unicast addresses in IPv6 are globally identifiable and uniquely addressable.

 

[Image: Global Unicast Address]

Global Routing Prefix: The most significant 48-bits are designated as Global Routing Prefix which is assigned to specific autonomous system. The three most significant bits of Global Routing Prefix is always set to 001.

Link-Local Address

                                               Auto-configured IPv6 address is known as Link-Local address. This address always starts with FE80. The first 16 bits of link-local address is always set to 1111 1110 1000 0000 (FE80). The next 48-bits are set to 0, thus:


 

[Image: Link-Local Addres

Link-local addresses are used for communication among IPv6 hosts on a link (broadcast segment) only. These addresses are not routable, so a Router never forwards these addresses outside the link.

Unique-Local Address

                                                                              This type of IPv6 address is globally unique, but it should be used in local communication. The second half of this address contain Interface ID and the first half is divided among Prefix, Local Bit, Global ID and Subnet ID.

 

[Image: Unique-Local Address]

Prefix is always set to 1111 110. L bit, is set to 1 if the address is locally assigned. So far, the meaning of L bit to 0 is not defined. Therefore, Unique Local IPv6 address always starts with ‘FD’.

Scope of IPv6 Unicast Addresses:

 

 

[Image: IPv6 Unicast Address Scope]

The scope of Link-local address is limited to the segment. Unique Local Address are locally global, but are not routed over the Internet, limiting their scope to an organization’s boundary. Global Unicast addresses are globally unique and recognizable. They shall make the essence of Internet v2 addressing.

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OSI Model

The Open Systems Interconnection model (OSI model) is a conceptual model that characterizes and standardizes the communication functions of a telecommunication or computing system without regard to their underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard protocols. The model partitions a communication system into abstraction layers. The original version of the model defined seven layers.

Layer 1 Physical Layer: It conveys the bit stream to electrical impulse, light or radio signal through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.

Layer 2 Data Link Layer: At OSI Model, Layer 2, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization and flow control. The FCS (Frequency Check Sequence) extra error-detecting code added to a frame in a communications protocol.

Layer 3 Network Layer: Layer 3 provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing, internetworking, error handling, congestion control and packet sequencing.

Layer 4 Transport Layer: OSI Model, Layer 4, provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.

Layer 5 Session Layer: This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.

Layer 6 Presentation Layer: This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.

Layer 7 Application Layer: OSI Model, Layer 7, supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.

Network