Explain which protocol does this, Similarly give a protocol which does the reverse mapping.

• The difference between MAC and IP address is shown below:

• Need to map an IP address to MAC(Physical) address:

  i. The packets from source to destination hosts pass through physical networks.At the physical level the IP address is not useful but the hosts and routers are recognized by their MAC addresses.

  ii. A MAC address is a local address.It is unique locally but it is not unique universally.

  iii. The IP and MAC address are two different identifiers and both of them are needed,because a physical network can have two different protocols at the network layer at the same time.

  iv. So to deliver a packet to a host or a router,we require two levels of addressing namely IP addressing and MAC addressing.

• Mapping of IP address to MAC address:

  i. The ARP(Address Resolution Protocol) maps an IP address to a MAC address whereas the RARP(Reverse Address Resolution Protocol) maps a MAC address to an IP address.

  ii. The router or host A who wants to find the MAC address of some other router,sends an ARP request packet. This packet consists of IP and MAC addresses of the sender A and the IP address of the Receiver(B).

  iii. This request packet is broadcasted over the network as shown in Figure 4.1

iv. Every host and router on the network receives and processes the ARP request packet. But only the intended receiver (B) recognizes its IP address in the request packet and sends back an ARP response packet.

v. The ARP response packet contains the IP and physical addresses of the receiver(B).This packet is delivered only to A(unicast) using A’s physical address in the ARP request packet.