IPv4

- Overview

Internet Protocol Version 4 (IPv4) was actually the first version of IP used. It was introduced back in 1983 and even today it is still the most famous version for identifying network devices.

IPv4 uses 32-bit addresses, which is the format you're probably most familiar with when discussing "IP addresses." This 32-bit address space provides nearly 4.3 billion unique addresses, although some IP blocks are reserved for special uses.

- IPv4 Addressing

IPv4 is a connectionless protocol. It operates on a best effort delivery model, in which neither delivery is guaranteed, nor proper sequencing or avoidance of duplicate delivery is assured. 

IPv4 is defined and specified in IETF publication RFC 791.e Internet Protocol and a widely used protocol in data communication over different kinds of networks. It is a connectionless protocol used in packet-switched layer networks, such as Ethernet. IPv4 provides a logical connection between network devices by providing identification for each device. There are many ways to configure IPv4 with all kinds of devices - including manual and automatic configurations – depending on the network type. 

IPv4 uses 32-bit addresses for Ethernet communication in five classes: A, B, C, D and E. Classes A, B and C have a different bit length for addressing the network host. Class D addresses are reserved for military purposes, while class E addresses are reserved for future use. 

IPv4 uses 32-bit (4 byte) addressing, which gives 232 addresses. IPv4 addresses are written in the dot-decimal notation, which comprises of four octets of the address expressed individually in decimal and separated by periods, for instance, 192.168.2.6.

- IPv4 Datagram Header

• VERSION: Version of the IP protocol (4 bits), which is 4 for IPv4.
• HLEN: IP header length (4 bits), which is the number of 32 bit words in the header. The minimum value for this field is 5 and the maximum is 15. 
• Type of service: Low Delay, High Throughput, Reliability (8 bits).
• Total Length: Length of header + Data (16 bits), which has a minimum value 20 bytes and the maximum is 65,535 bytes. 
• Identification: Unique Packet Id for identifying the group of fragments of a single IP datagram (16 bits). 
• Flags: 3 flags of 1 bit each : reserved bit (must be zero), do not fragment flag, more fragments flag (same order). 
• Fragment Offset: Represents the number of Data Bytes ahead of the particular fragment in the particular Datagram. Specified in terms of number of 8 bytes, which has the maximum value of 65,528 bytes. 
• Time to live: Datagram’s lifetime (8 bits), It prevents the datagram to loop through the network by restricting the number of Hops taken by a Packet before delivering to the Destination. 
• Protocol: Name of the protocol to which the data is to be passed (8 bits). 
• Header Checksum: 16 bits header checksum for checking errors in the datagram header.

[More to come ...]