ARP

how-arp-works-2

Address Resolution Protocol (ARP)

ARP (Address Resolution Protocol) is a Layer 2 Protocol. Layer 2 uses Physicall addresses (MAC addresses) for the communication. Here, ARP is used to convert a given IP address to the related hardware address (MAC Address) to provide this. This important duty makes this protocol a key protocol for Ethernet based networks.

Basically for the transfer of the IP packets in a network, beside the IP adddress, the destination hardware address (MAC Address) also must be known by the sender (Source). If this destination MAC Address is known, then the source can send this packet to the destination. But if the destination MAC Address is not known, before the transmission, it must learn this MAC Address.

How does ARP Works?

We can explain ARP (Address Resolution Protocol) operation in three different case. These three different case also has its own ARP type. These cases and the ARP types are:

ARP (ARP Operation in a Network)
Proxy ARP (ARP Operation Between Networks)
Gratuitous ARP (Duplicate IP Check)

The first case, is the basic ARP operation in a single network, in one broadcast domain.

The second case (Proxy ARP), is the ARP operation between one more broadcast domains. Proxy ARP enables data link discovery between networks.

Gratuitous ARP, is the ARP that is used to check if an IP is used by another device in the network.

Let’s explain these ARP cases.

ARP Packet

ARP Packet is consist of some main parts. Below you can find these parts.


arp-packet-format

ARP Operation

ARP Operation can be explained in soem basic steps Here, for the explanation of ARP Operation, we will use an example. Our example topology will be like below:


how-arp-works-1

Lesson tags: arp
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