TCP/IP Volume One reading note (3) Why both IP addresses and MAC addresses are also available

Network layer

First, it is clear that not all of the transmission of data between the network requires a MAC address and IP address, such as point-to-point lines of communication between the MAC address, the network layer using the IPX protocol when there is no IP address, but in the current mainstream network, we use the IP address and MAC address

Since the MAC address is unique, why should I have an IP address?

Before we mentioned that the MAC address is unique, and theoretically, between any two devices, I should be able to send data through the MAC address, why do I need an IP address?

MAC address is like a personal ID number, the person's ID number and the city of the person's account, the date of birth is related, but there is no relationship with the person's location, people will move, know a person's ID number, can not find it this person, MAC address similar, it is and equipment producers, batches, Dates and the like are associated with knowing a device's Mac and cannot send data to it in the network unless it is within the same network as the sender.

So to achieve the communication between machines, we also need to have the concept of IP address, the IP address is the current machine in the network location, similar to the city name + road number + The concept of house numbers. By addressing the IP layer, we can know which path to transfer data between machines on any two internet-based computers around the world.

MAC addresses are usually constant, IP addresses are variable, especially mobile devices, and IP addresses are often changed.

MAC address design does not carry the device in the network location information, want to communicate through the MAC address, we have to maintain a large table on all devices, record all the MAC address routing in the current position of the next hop, which is obviously unreasonable.

Since you can send data over an IP address, why do I have a MAC address?

Since the IP address has location information and is unique in a network, why don't we completely communicate by IP address and discard the MAC address? Or, merging the capabilities of the IP layer and the MAC layer.

• Historical reasons
  The initial link layer protocol is independent of the IP address, there is no network layer settings, only the physical layer and the link layer, initially only the hub, no switch router, the server between the transfer of data by MAC address. The MAC address is already in use before the IP address is available. The two-layer switch, which is now used everywhere, is to forward data based on the MAC address.

• The reason for the design
  Now this design is good design, the implementation of the link layer does not need to consider the data between the forwarding, network layer implementation does not need to consider the impact of the matter layer.

In other words, theoretically feasible, there is no great significance at present, but there are disadvantages.

TCP/IP Volume One reading note (3) Why both IP addresses and MAC addresses are also available