why do we need to map ip address to mac address?

Question

i know that it is use for multicasting but why?

Answer 1

First off, it's for scalability. If we just used MAC addresses for communications then we would not be able to "route" and we would have MAC address tables (Bridge/Switch tables) containing, what, billions of addressess?

By mapping and IP address to a MAC address we can create a layer of abstraction, and we can make that layer conform to a hierachy. Now instead of directly addressing an end point by it's MAC address, we reference it by it's IP address. If the IP address is known to be remote (not = to the senders IP subnet) then we just send it to a router, and based on the network portion of the destination address the routers will forward it on until it reaches a router that is directly connected to the desired end point (that router has a directly connected interface to that specific subnet). That router will then send the packet to the end point's MAC address. The router can use ARP to map the IP-to-MAC or it may already have it in it's table.

That end point will associate the original senders IP address with the routers MAC address.

So the IP layer communications is predicated on MAC layer communications (which is predicated on an electrical connection with most mediums).

Another reason that the layer of abstraction helps is that it allows us to change MAC addresses without having to change IP addressess. And of course IP addressess can be mapped to "names", so I can change my hardware address but I can still be found using the same name or IP address.

End point-to-end point communications usually take place on a MAC-to-MAC (or unicast basis), but as you mentioned you can also have communications using multicast, and of course, broadcast. Unicast is the most efficient because only the adaptor with the specific MAC address in the destination header will bother to accept and process the frame, with multicasting multiple adpators will be listening for a specific destination address, but many other adaptors will not be and thus will not bother to accepts and process the frame. With a broadcast, pretty much everyone on a local segment has to accept and process the frame, and this is why broadcast need to be isolated and kept to a minimum - it just creates too much overhead.

Answer 2

In simple words: - MAC address is the hardware address of the network interface to which you are actually communicating. When a network device is manufactured, it is assigned with only MAC address, not IP address. The IP address is assigned later when the device is used in a network and it can be changed whenever we want. Since IP address is the address supported by Internet Protocol, it needs to be binded with MAC address of the device.

Answer 3

Computers talk to each other using a unique MAC address which is a Hexadecimal number given to the network card by the manufacture,
Networks talk to each other up to the Router by using IP address that are four 3 number groups given to the network by the ISP.
The Routers then resolve the numbers to mac address's
(A VERY SIMPLIFIED VERSION)

Answer 4

You are referring to Layer 2 and Layer 3 routing in the 7 layer OSI model. Layer 2 (or LAN) routing is done by MAC addresses. Layer 3 routing (internet) is done by IP address. The ARP command (address resolution protocol) is what is used to convert or view IP to MAC and vice versa.

Answer 5

Actually, it's used for all IP communication.