Most network data transmission technologies use packets to transmit data from a source device to destination. The IP protocol is not exception. IP packets are the most important and fundamental components of the protocol.
The two main functions of the IP protocol are routing and addressing. To route packets to and from machines on a network, IP uses IP addresses which are carried along in the packets. A lot of other information are carried along as well, in the packet header. The structure of an IP packet is shown in the picture here.
The brief descriptions in the picture are meaningful enough to give you an idea of the function of the header elements. However, some might not be clear:
- The identification tag is used to help reassemble the packet from several eventual fragments.
- The fragmented flag states whether the packet can be fragmented or not.
- The fragment offset is a field to identify which fragment this packet is attached to.
- Time to Live (TTL) is a number that indicates how many hops (router passes) the packet can make before it dies. This is done to prevent a packet from remaining forever on a network, thus causing congestion. TTL is decremented at each hop.
- The header checksum is a number used for error detection and correction during packet transmission.
Notice that data payload can be up to 64 KiloBytes, which is huge compared to the totality of the header bits.
