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The entire process is illustrated in this animation: Since the target knows who sent the initial ARP Request, it is able to send the ARP Response unicast, directly back to the initiator. The node which is the target of the ARP Request will then send an ARP Response back to the original sender. The nodes which are not the intended target will silently discard the packet. All nodes will take a look at the content of the ARP request to determine whether they are the intended target. Since it was a broadcast, all nodes on the network will receive the ARP Request. This request must be a broadcast, because at this point the initiator does not know the target’s MAC address, and is therefore unable to send a unicast frame to the target. It starts with the initiator sending an ARP Request as a broadcast frame to the entire network. The Address Resolution itself is a two step process – a request and a response. If a Router is delivering a packet to the next Router in the path to the host, the ARP target will be the other Router’s Interface IP address – as indicated by the relative entry in the Routing table. In the same way, if a Router is delivering a packet to the destination host, the Router’s ARP target will be the Host’s IP address. If a host is speaking to another host on a different IP network, the target for the ARP request will be the Default Gateway’s IP address. If a host is speaking to another host on the same IP network, the target for the ARP request is the other host’s IP address. The “next NIC” in the path will become the target of the ARP request.

The purpose for creating such a mapping is so a packet’s L2 header can be properly populated to deliver a packet to the next NIC in the path between two end points. Use the navigation boxes to view the rest of the articles.Īs we’ve learned before, the Address Resolution Protocol (ARP) is the process by which a known 元 address is mapped to an unknown L2 address. This article is a part of a series on Address Resolution Protocol (ARP).