Protocols ARP, RARP, IP, ICMP. What is ARP used for?

If the machine communicates with another equivalent device on the same network, this connection requires a physical or MAC address. However, the application responsible for communication requires the use of some mechanism that can associate the IP address with the MAC address.

This mechanism is implemented using address resolution protocols (ARP). Due to them, the IP address of the destination node is broadcast, which informs the source of the MAC address. Thus, ARP protocols facilitate communication between two devices when they are simultaneously connected to a network.

How it works?

This means that every time the machine A wants to send data packets to machine B, A must send an ARP packet to request MAC address B. However, this inevitably will lead to an increase in the load on the network and the increase in traffic.

In order to reduce traffic and costs for network connections, computers using the ARP protocol support the cache of newly acquired IP_to_MAC binding addresses, that is, they do not need to use ARP again.

At the same time, some refinements of ARP are possible: when machine A wants to send data to machine B, it is possible that B is going to send back data A in the near future. Therefore, to avoid using ARP for machine B, A must store its IP_to_MAC binding address in a special packet when requesting MAC address B. Since A passes its initial request to MAC address B, each machine on the network must be extracted and stored in Its address is IP_to_MAC.

When the device is on the network (for example, if the operating system is rebooting), it can broadcast the binding address so that all other machines can save it in their settings. This will not reuse the ARP protocols that might be needed when connecting other new devices.

Example of displaying the use of the address resolution protocol

You can consider a scenario where the computer is trying to communicate with some remote devices, and previously there was no exchange of IP between them. That's why the ARP protocol must be applied - to determine the MAC address of the remote machine.

The ARP request message (which comes from the AAAA IP address to the BBBB) is broadcast over a local network with the Ethernet protocol type. ARP protocols originate from all machines except the target, which sends a response message to the request. This answer contains the IP-address of the BBBB, i.e. The hardware address of the Ethernet source, after which communication will be established between the devices.

ARP protocol and its purpose - conclusions

As can be seen from the description above, the address resolution protocol is used to establish the interaction between various devices on the network. In other words, this is a technology without which a normal connection is not possible. But is ARP possible without other network parameters? Definitely impossible. Therefore, other protocols that play an important role should be considered.

Recover address recovery protocol

RARP is a protocol by which a physical computer on the local network can request its IP address from the Address Resolution Protocol table or gateway cache server. The network administrator creates a table in the gateway or router of the local network that displays the physical address of the machine (or MAC address) relative to the corresponding protocol. When a new device is connected to the network, its RARP client creates a request on the server to send its IP address. Assuming that the entry was created in the router table, the RARP server returns the IP address to the machine, which can store it for later use. Thus, the ARP address resolution protocol is continuously linked to RARP.

Detailed mechanism

Both the machine that issues the request and the server that responds to it-they all use physical network addresses during a communication session. Typically, the requestor does not know the physical address. Thus, the request is broadcast to all machines on the network. The requesting party must then identify itself with the server. For this, the serial number of the CPU or the physical address of the network machine can be used. The use of a physical address as a unique identifier has two advantages.

These addresses are always available and should not be linked in the boot code.
Because the identifying information depends on the network, and not on the vendor of the CPU, all machines on the network will have unique identifiers.

RARP action in time

Since RARP uses a physical network directly, no other protocol software will respond to the request or relay it. The RARP software must deal solely with these tasks. Some workstations that rely on RARP for downloading may repeatedly attempt an undefined time until they receive a response. Other implementations have a failure after several attempts to avoid network overloading by unnecessary broadcasts.

IP / ICMP / ARP Protocols

The ICMP protocol links the mechanism, gateways, and hosts that are used to manage a connection or receive an error report. The Internet protocol provides a signal from the gateway to the gateway until it reaches a point that can deliver it directly to its final destination. If the gateway can not send or deliver data, or it detects an unusual condition such as network congestion, it should report this to take measures to avoid or fix the problem.

The Internet Message Control Protocol (ICMP) allows gateways to transmit errors or manage messages to other gateways or hosts. Thus, ICMP provides communication between Internet protocols on both connected computers.

This special mechanism was added by developers in addition to TCP / IP protocols. It allows you to use gateways on the Internet to report errors or provide information about emergencies. The IP protocol itself does not contain anything that can help to check the connection with the sender or learn about the failures.

TCP / IP Protocols

TCP / IP protocols provide tools that can help network administrators or users identify network problems. One of the most commonly used debugging tools calls the ICMP request and receives a response message. At the same time, the host or gateway sends an echo message with an ICMP request to the specified address. Any machine that receives an echo request formulates a response and returns to the original sender. In this case, the response contains a copy of the data transmitted in the request, as well as the associated response.

This protocol can be used to verify whether the addressee is available and whether communication is possible with it. In turn, the ARP protocols are hardware used in addition to TCP / IP and necessary for making correct communication between devices in the network.