Internet Protocol Version 4 (IPv4) - Everything you need to know

a. What is Internet Protocol? Explain the characteristics of IPv4
IP stands for Internet Protocol and v4 stands for Version Four (IPv4). IPv4 was the primary version brought into action for production within the ARPANET in 1983. IP version four addresses are 32-bit integers which will be expressed in decimal notation. 
Example- could be an IPv4 address. 
What is IPv4 Address? Conversion and Datagram format Explained!!!

Characteristics of IPv4
• IPv4 could be a 32-Bit IP Address.
• IPv4 could be a numeric address, and its bits are separated by a dot.
• The number of header fields is twelve and the length of the header field is twenty.
• It has Unicast, broadcast, and multicast style of addresses.
• IPv4 supports VLSM (Virtual Length Subnet Mask).
• IPv4 uses the Post Address Resolution Protocol to map to the MAC address.
• RIP may be a routing protocol supported by the routed daemon.
• Networks ought to be designed either manually or with DHCP.
• Packet fragmentation permits from routers and causing host.

b. What is IP header? Explain the IP header format and components of IPv4?
IPV4 header format is of 20 to 60 bytes in length, contains information essential to routing and delivery, consist of 13 fields, VER, HLEN, service type, total length, identification, flags, fragmentation offset, time to live, protocol, header checksum, source IP address, Destination IP address and option + padding, where each has its own features and provides essential data required to transmit the data.

Header Format Component
· Version: The first header field is a 4-bit version indicator. In the case of IPv4, the value of its four bits is set to 0100, which indicates 4 in binary.

· Internet Header Length: IHL is the 2nd field of an IPv4 header, and it is of 4 bits in size. This header component is used to show how many 32-bit words are present in the header. As we know, IPv4 headers have a variable size, so this is used to specify the size of the header to avoid any errors. This size can be between 20 bytes to 60 bytes.

· Type of Service: ToS is also called Differentiated Services Code Point or DSCP. This field is used to provide features related to service quality, such as for data streaming or Voice over IP (VoIP) calls. It is used to specific how a datagram will be handled.

· Explicit Congestion Notification: ECN is used to send notifications to the sender or receive in situations where network congestion happens.

· Total Length: This field’s size is 16 bits, and it is used to denote the size of the entire datagram. The minimum size of an IP datagram is 20 bytes, and at the maximum, it can be 65,535 bytes. Practically, all hosts are required to be able to read 576-byte datagrams.

· Identification: The identification or ID field in a packet can identify an IP datagram’s fragments uniquely. Some have suggested using this field for other things such as adding information for packet tracing etc.

· Flags: flag in an IPv4 header is a three-bit field that is used to control and identify fragments. The following can be their possible configuration:
o Bit 0: this is reserved and must be set to zero
o Bit 1: DF or do not fragment
o Bit 2: MF or more fragments.

· Fragment Offset: This field is 13 bit long in length, and it is measured by blocks that units of 8-byte blocks. These are used to specify the offset of a fragment relative to the start of the IP datagram, which when it was not fragmented. As you can expect, the first offset of a fragment is always set to zero.

· Time to live: Time to live (or TTL in short) is an 8-bit field to indicate the maximum time the datagram will be live in the internet system. The time here is measured in seconds, and in case the value of TTL is zero, the datagram is erased.

· Protocol: This is a filed in the IPv4 header reserved to denote which protocol is used in the later (data) portion of the datagram. For Example, number 6 is used to denote TCP and 17 is used to denote UDP protocol.

· The header’s checksum: The checksum field is of 16-bit length, and it is used to check the header for any errors. The header is compared to the value of its checksum at each hop, and in case the header checksum is not matching, the packet is discarded.

· Source Address: It is a 32-bit address of the source of the IPv4 packet.

· Destination Address: the destination address is also 32 bits in size, and it contains the receiver’s address.

· Options: This is an optional field of the IPv4 header. It is used only when the value of IHL is set to more than 5. These options contain values and settings for things related to security. Record route and time stamp etc.

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