Shulou(Shulou.com)06/01 Report--

1. Direct mapping:

The basic idea: Choose a method for Layer 2 and Layer 3 addresses, which uses a simple algorithm (or a formula) to get another address from one address.

b. A simple example: assume that the layer 2 address is smaller than the layer 3 address; an IP address (layer 3 address) is 222.101.33.29. Since the layer 2 address is smaller than the layer 3 address, the last octet of the IP address of the network can be used as a link layer address. In this way, the IP address 222.101.33.29 can be assigned to the device with address #29 of the network.

c。Graphical process of direct mapping:

222101332911011110011001010010000100101001

IP address of 32b (222.101.33.29)

where the last 8 bits, the decimal 29 bits, are a MAC address corresponding to the address of the corresponding hardware device (address #29 device)

Note that direct mapping is limited to cases where the layer 2 address is smaller than the layer 3 address.

2. Dynamic address resolution:

In order to meet the MAC address is larger than the IP address, when more flexibility is needed, dynamic resolution is selected instead of direct mapping.

A. What is dynamic analysis?

It is a special protocol that allows devices with only IP addresses to determine their corresponding data link layer addresses.

If the two address types have completely different formats, the device with the IP address typically queries one or more other devices in the local network to determine the data link layer address to which the IP address corresponds.

b. Dynamic addressing process:

Suppose device 1 sends data to device 2, but device 1 knows only the network layer address of device 2 and not the data link layer address. Therefore, device 1 broadcasts a layer 2 frame containing the layer 3 address of device 2, and only device 2 recognizes the layer 3 address in the frame broadcast by device 1. Once identified, a response is sent directly back to device 1.

You could say,

The device that wants to send data broadcasts a request for a response from the device that has the hardware address (MAC address). Device 1 needs to send data to Device 2, but only knows its IP address but not its MAC address. device 1 broadcasts a request to return the MAC address of device 2 using the IP address. Device 2 returns directly to Device 2 with its MAC address.

c. Dynamic address cache:

Why cache dynamic addresses?

The answer is that since the Layer 2 address of the receiver is not known, the Layer 2 frame of the Layer 3 address of the receiver device is broadcast every time. As a result, many devices in the local network must consume resources to examine the data frame and check the IP address it is trying to resolve.

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