Internet Protocol (IP): The Internet Protocol (IP) is a network-layer (Layer 3) proscel that contains addressing information and some control information that enables packets to be routed. IP is the primary network-layer protocol in the Internet protocol suite. Along with the Transmission Control Protocol (TCP), IP represents the heart of the Internet protocols IP bas two primary responsibilities: providing connectionless, best-effort delivery of datagrams through an internetwork and providing fragmentation and reassembly of datagrams to support data links with different maximum transmission unit (MTU) sizes.
A. IP Packet Format: An IP packet contains several types of information, as illustrated
Fig. Fourteen fields comprise an IP packet
The following discussion describes the IP packet fields illustrated in figure
(i) Version: It indicates the version of IP currently used.
(i) IP Header Length (THL): It indicates the datagram header length in 32-bit words.
(iii) Type of Service: It specifies how an upper-layer protocol would like a current
datagram to behandled and assigns datagrams various levels of importance.
(iv) Total Length: It specifies the length, in bytes, of the entire IP packet, including the
data and header.
(v) Identification: It contains an integer that identifies the current datagram. This field is used to help piece together datagram fragments.
(i) Flags: It consists of a 3-bit field of which the two low-order (least-significant) bits control fragmentation. The low-order bit specifies whether the packet can be fragmented. The middle bit specifies whether the packet is the last fragment in a series of fragmented packets. The high-order bit is not used.
(vii) Fragment Offset: It indicates the position of the fragment's data relative to the beginning of the data in the original datagram, which allows the destination IP process to properly reconstruct the original datagram.
(viii) Time-to-Live: It maintains a counter that gradually decrements down to zero, at which point the datagram is discarded. This keeps packets from looping endlessly.
(ix) Protocol: It indicates which upper-layer protocol receives incoming packets after IP processing iscomplete.
(x) Header Checksum: It helps ensure IP header integrity.
(xi) Source Address: It specifies the sending node.
(xii) Destination Address: It specifies the receiving node.
(xiii) Options: It allows IP to support various options, such as security.
(xiv) Data: It contains upper-layer information.