An internet is made of a combination of physical networks connected by internetworking devices such as routers. When packet wants to transmitted from one host to another host it started its journey from source host. It has to pass through several router and then reached destination router. In between there has many LAN or WAN. When data starting its journey it has to pass many physical networks router to router, router to switch but all the router cannot take the data packet because the packet not for that router but how can they identify that. The host and router recognize at the network level by their IP address. They check their IP address and decided that they should receive the packet or not.
Packets have to also pass through physical network to reach host to routers. They pass several physical network to reach in their destination. At the physical level, the hosts and routers are recognized by their physical addresses. Physical address is a local address. Its authority is a local network. But the physical address must be unique locally. But it is not unique globally.it may use in other local networks. But this address are reserved. When they transmitted nearest router change its physical address and gives a unique address. When it reach to the destination’s router that router checked source address are same to destination address. Then destination router receive the packet. Physical address is called physical address because generally it is implemented in the hardware. Normally physical address contains 48 bit mac address in the Ethernet protocol. When a hardware is made that time this mac address is implemented.
Physical address and logical address are two different address. They are not same address. Physical address is in the hardware and IP address is given by internet protocol to transfer data to the exact location. But we need both of the address for delivering data. In the physical layer there use to protocol IP and IPX protocol at the same time. That means when we wants to transfer data we need both physical address and logical address. For maintaining this two address we need to track them. For tracking we need map. Using map we can track them. As delivering a packet we need physical address and corresponding to logical address there need a mapping system. Like we need to map physical address corresponding logical address and logical address corresponding to physical address. We can map this things using two mapping system static or dynamic mapping.
Static Mapping create a table which contains a logical address with a physical address. All of this information is stored in the machine. Machine knows all the information. But there has a problem, physical address of a device can be changed in other network.
Limitations are given bellow:
1. A machine could change its NIC, realizing another physical address
2. In a few LANs, for example, Local Talk, the physical address changes each time the PC is turned on.
3. A flexible PC can move beginning with one physical framework then onto the following, achieving an alteration in its physical address
To actualize these progressions, a static mapping table must be refreshed occasionally. This overhead could influence organize execution. In dynamic mapping each time a machine knows one of the two locations, it can utilize a convention to locate the other one.
Mapping logical to Physical Address:
Whenever a host or a switch has an IP datagram to send to another host or switch, it has the logical (IP) address of the receiver. The logical (IP) address is gotten from the DNS if the sender is the host or it is found in a steering table if the sender is a switch. Be that as it may, the IP datagram must be epitomized in a casing to have the capacity to go through the physical system. This implies the sender needs the physical address of the beneficiary. The host or the switch sends an ARP inquiry parcel. The parcel incorporates the physical and IP locations of the sender and the IP address of the collector. Since the sender does not know the physical address of the beneficiary, the inquiry is communicated over the system.
Each host or switch on the system gets and forms the ARP question bundle, however just the expected beneficiary perceives its IP address and sends back an ARP reaction parcel. The reaction bundle contains the beneficiary’s IP and physical locations. The bundle is unicast specifically to the inquirer by utilizing the physical address got in the question parcel.