IP Protocol:

1. IP Protocol Stands for Internet Protocol.
2. It is host to host network layer delivery protocol designed for the internet.
3. It is connectionless datagram protocol.
4. It is unreliable protocol because it does not provide any error or flow control.

Function of IP Protocol:

I) Addressing:

 IP packet headers contain addresses that identify the sending computer and the receiving computer.

 Routers use this information to guide each packet across communication networks and connect the sending and receiving computers.

II) Reassembly:

 Messages between computers are broken into packets.

 Since most messages are too big to fit in one packet, and since packets aren't sent in any organized order.

 So they must be reassembled as they arrive at the recipient.

 IP dictates how packets are reassembled into usable messages.

III) Timeouts:

 Each IP packet contains a Time to Live (TTL) Field.

 Every time when router handles a packet, TTL field is decremented.

 If TTL reaches zero then packet is discarded.

 This prevent the packet from running in circles forever and flooding a network.

IV) Fragmentation:

 IP Packets may be split, or fragmented into smaller packet.

 This permits a large packet to travel across a network which can only handle smaller packets.

 IP Fragments packets transparently.

V) Type of Service:

 IP supports traffic prioritization by allowing packets to be labeled with an abstract type of service.

VI) Options:

 IP includes optional features such as allowing the sending computer to decide the path.

 To trace the path they take.

 To include added security in the packets.

IP Header Format:

I) Version: This Field defines the version of IP. It is Static 4 bit value.

II) Header Length: This Field defines the length of the datagram header. It is 4 bit value.

III) Type of Service: It is 8 bit value. It is used tell the network how to treat the IP packet. These bits are generally used to indicate the Quality of Service (QoS) for the IP Packet.

IV) Packet Length: 16 bit value indicating the size of the IP Packet in terms of bytes. This gives a maximum packet size of 65536 bytes.

V) Identification: 16 bit field used for reassembling the packet at the destination.

VI) Flags: It is 3 bits value. It indicates if the IP packet can be further fragmented or not and if the packet is the last fragment or not of a larger transfer.

VII) Fragment offset: 13 bit value used in the reassembly process at the destination.

VIII) Time to Live: 8 bit value telling the network how long an IP packet can exist in a network before it is destroyed.

IX) Protocol: 8 bit value used to indicate the type of protocol being used (TCP, UDP etc.).

X) Header checksum: It is 16 bit value. It is used to indicate errors in the header only. Every node in the network has to check and re-insert a new checksum as the header changes at every node.

XI) Source address: 32 bit value representing the IP address of the sender of the IP packet.

XII) Destination address: 32 bit value representing the IP address of the packets final destination.

XIII) Options: Options are not required for every datagram. They are used for network testing and debugging.

XIV) Padding: Variable size bit field. These bits are used to ensure a 32 bit boundary for the header is achieved.