ARP Address Resolution Protocol < Two >--Address resolution mapping

1. Direct mapping:

A, the basis of the basic idea: to the 2nd and 3rd address Select a method, this method uses a simple algorithm (also can be a formula), from one address to get another address.

b, a simple example: assuming that the 2nd address is smaller than the 3rd address , an IP address (layer 3rd address) is 222.101.33.29, because the 2nd address is smaller than the 3rd address, then you can use the net IP address of the last eight-bit group as a link-layer address, so that the IP address can be 222.101.33.29 assigned to the network's #29 address of the device

C. Diagram process for direct mapping:

222	101	33	29
11011110	01100101	00100001	00101001

32b IP address (222.101.33.29)

Where the last 8-bit group, which is the decimal 29, is a MAC address that corresponds to the address of the corresponding hardware device (#29地址设备)

D, note that direct mapping is limited to situations where the 2nd address is smaller than the 3rd address.

2, dynamic Address resolution:

In order to satisfy the MAC address greater than the IP address, when more flexibility is needed, select dynamic parsing instead of direct mapping.

A, what is dynamic parsing?

It is a special protocol that allows a device with only an IP address to determine the corresponding data link layer address.

If the type of the two addresses has a completely different format, the IP address of the device is usually queried by one or more of the other devices on the local network to determine the IP address corresponding to the data link layer address.

B. The working process of dynamic addressing:

Assume that device 1 sends data to device 2, but device 1 knows only that the network layer address of device 2 does not know the address of the data link layer. Therefore, device 1 broadcasts a layer 2nd frame containing the 3rd address of Device 2, and only device 2 identifies the 3rd layer address in the frame of the device 1 broadcast. Once identified, a response is sent back directly to device 1.

It can also be said that

The device that is sending the data broadcasts a request that requests a response from that device with that hardware address (MAC address). Device 1 needs to send data to device 2, but only knows his IP address and does not know its MAC address. Device 1 broadcasts a request that returns the MAC address of the device 2 that uses the IP address. Device 2 Returns the device 2 directly with his MAC address.

C, dynamic address cache:

Why should I have a cache of dynamic addresses?

The answer is that because you do not know the 2nd address of the receiver, each time you broadcast the 2nd-layer frame of the 3rd-tier address of the receiving device. As a result, many devices in the local network must consume resources to validate the data frame and check the IP address it is parsing.

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ARP Address Resolution Protocol < Two >--Address resolution mapping