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

1. Basic operations of ARP:

Is the transmission of a pair of requests and responses in the local network.

Understanding: the source (the device that sends the IP Datagram) sends a broadcast containing information about the destination (the party receiving the Datagram), and the destination uses unicast to send back a response to the source telling the source the MAC address of that destination.

2. ARP message type:

First, two different messages are sent in ARP, from source to destination and from destination to source. The sender sends the message and the target receives the message. The identity of the sender and the target party is different for each message, depending on the specific situation.

3. How is the identity of the sender and the target party used for requests and responses?

First of all, let's introduce four key words:

Request, answer, hardware address, protocol address

These addresses have a specific location in the ARP message format.

A. for the sender:

Request: the sender is the source and the destination is the destination

Answer: the sender is the destination and the destination is the source

Sender hardware address: the layer 2 address of the sender in the ARP message

Sender protocol address: the layer 3 address of the sender in the ARP message

B, for the target party

Request: the destination is the source and the sender is the destination

Answer: the destination is the destination and the sender is the source

Hardware address of the target party: layer 2 address of the target party in the ARP message

The protocol address of the destination party: the layer 3 address of the destination party in the ARP message

4. ARP general operation (in ARP transactions, the order in which messages are exchanged between source and destination devices):

A, source device detection cache

B. The source device generates an ARP request message

C. The source device broadcasts the ARP request message

D. The local device processes the ARP request message

E. The destination device generates an ARP reply message

F. The destination device updates the ARP cache

G. The destination device sends the ARP cache

H. The source device processes the ARP reply message

I. The source device updates the ARP cache

5. ARP message format:

Hardware type protocol type hardware address length protocol address length opcode sender hardware address sender protocol address target hardware address target protocol address

A, ARP message format:

The field name length describes the HRD2 hardware type, defines the type of hardware used to transmit ARP messages on the local network, and identifies the type of address used. PRO2 protocol type, which defines the type of layer 3 address in the message HLN1 hardware address length PLN1 protocol address length OP2 opcode, defines the nature of the ARP message to be sent, and defines many other values to support other protocols using ARP frame format SHA variable, equal to the HLN field value sender hardware address, the hardware address of the device sending the message is the IP Datagram source device in the request or the IP Datagram destination device in the answer SPA variable, equal to the PLN field value sender protocol address, the IP address THA of the device sending the message is variable, equal to the HLN field value target hardware address, and the device hardware address to which the message is to be sent Is the destination device of the IP Datagram in the request or the device of the IP Datagram source in the reply TPA variable, which is equal to the destination protocol address of the PLN field value, and the IP address of the device to which the message is to be sent

B, ARP hardware type HRD field value:

Value of HRD hardware Type 1 Ethernet 6IEEE 802 Network 7ARCNet15 frame Relay 16ATM Asynchronous transfer Mode 17HDLC18 fibre Channel 19ATM Asynchronous Transmission Mode 20 Serial Link

C, ARP opcode field value:

Opcode ARP message type 1ARP request 2ARP answer 3RARP request 4RARP answer 5DRARP request 6DRARP answer 7DRARP error 8InARP request 9InARP answer

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