What is Internet Protocol?


Internet protocol or IP is the set of protocols that are responsible for routing packets from one machine to another over the Internet.  IP is only concerned with routing and as such is referred to as an unreliable protocol in that it does not care whether or not a packet actually arrives at the destination.  TCP breaks up the data into packets and adds a header to each packet.  The assembly and the address of the receiving machine is then passed on to IP in the layer below.  In other words TCP is a routine that calls the services of IP which is a routine in the layer below where TCP resides.


Where does IP fit into the OSI?





IP as with TCP adds its own header to the packet (that by now also includes the TCP header).  The main information that is placed in IP header are IP addresses of sender and receiver.   Receiver needs to know where the message is coming from and destination address is used by the gateways on the way to the destination.   Also in the header there is the number of protocol in the layer above that the packet needs to be forwarded to.  At this point message looks as follows;




This is the message that is passed on to the layer below. 


An example of an IP address could be  A combination of four decimal numbers, each of which is an 8-bit binary number.  So this IP address is 32 bit and it is for ease of presentation that it gets presented as four decimal numbers.


Part of the IP address identify the network where the host computer resides and the rest of it identify a host computer in that network.  Therefore each address can be thought of as a network address and a computer address in that network.  Which part of the IP address identifies the network depends on the type of the network and in effect on its potential size.  For very large corporation only the 1st 8 bits (from left) identify the network which would allow for high number of hosts.  These networks are the rarest and examples of these companies are BT and AT&T.  Type C networks are identified by the 1st 24 bits which means that this type of network is the most frequent (see an Example of IP address).


IP version 6 or IPv6 is the new standard for IP.  Why do we need this new standard?






IPv4 is 32 bits long.  How long is IPv6?





In case of Internet applications in order to access a remote computer on the Internet, IP address of the computer is required or another words we need to know where it is.  IP addresses are not easy to memorise and domain names are used.   This means that domain name has to be converted to its corresponding IP address through domain name service before the remote computer can be contacted.