ARP Concepts and Principles of Operation

This time, we're going to learn what ARP is and how it works. First of all, before I explain ARP, remember what the two addresses below mean.

 

Logical Address = IP Address

Physical Address = Local Address

 

 

1. ARP (Address Resolution Protocol)

 

 

What is ARP? : Converting logical addresses to physical addresses

 

 

- Order of operation when the terminal to communicate needs a physical address (Order in which ARP operates)

 

 

1. ARP Request

: The sender broadcasts the ARP request to all PCs connected to one network with the information of their origin MAC + origin IP + destination IP.

 

 

2. All PCs connected to the network receive this frame. PCs that do not have logical IP with them discard the received frame, and only the right PC sends a response.

 

 

3. ARP Reply

: A PC with a logical IP sends a response to the sender by adding its own MAC Address. When sending a response, send it to unicast, not Broadcast.

 

- Why use and why use ARP if ARP is used

 

: If you receive a packet without a MAC address, it is discarded at the second layer (Datalink-Layer), so you need to know the other party's MAC address to create a frame so that you can communicate.

 

The same network communicates with only MAC Address.

 

 

- Four things when ARP is used

 

1) The sender is host, and you want to send a packet to another host on the same network.

 

2) The sender is host, and you want to send a packet to another host on another network.

 

3) The router that received the datagram to the host on another network is the sender.

 

4) The router that received the datagram to the host on the same network is the sender.

 

 

 

※ The ARP request is broadcast ~~~~~~ The ARP response is unicast. Please remember.

 

 

* Cache table The use of the ARP protocol between the terminals to communicate with each other is very ~ inefficient, so we use the cache table. = This is what we call ARP Table.

 

Once received, the address is stored in the cache table for communication sent to the same recipient for the next few minutes.

 

ARP Table Aging Time on a Normal Switch

(The time that ARP is stored and erased from ARP Tale if it does not communicate for a certain period of time) is 300 seconds and 5 minutes.

 

The ARP table is re-generated when communication is made by shooting at the ping again.

 

 

 

 

2. RARP (Reverse Address Resolution Protocol)

 

※ Reverse Address Resolution Protocol (RARP): The task of converting a physical address to a logical address

 

RARP is used only in special cases, when a computer or device without a disk receives an IP from the RARP server when it is first powered on.

 

Diskless computers place critical data on a central server, allowing each client to download and use data from the server without disks, preventing users from installing programs arbitrarily on each client and minimizing the cost of the entire hardware.

 

 

 

 

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