Networking Academy - Networking Basics Module 13: The ARP Process

The Layer 2 Ethernet frame contains the following:

- Destination MAC Address - Source MAC Address

Two primary addresses assigned to a device on an Ethernet LAN:

- Physical Address (The MAC address) - Logical Address (The IP address)

The Layer 3 IP packet contains the following:

- Source IPv4 Address - Destination IPv4 Address

Neighbor Discovery Protocol (NDP)

A protocol that is part of the IPv6 protocol suite and is used to discover and exchange information about devices on the same subnet (neighbors). In particular, it replaces IPv4 ARP.

ARP Reply

An ARP message used to supply information about an ARP request. A device providing its MAC address in reply to a request

ARP - Step 2

Each host on the network receives the broadcast frame and compares the IPv4 address inside the message with its configured IPv4 address. The host with the matching IPv4 address sends its MAC address back to the original sending host.

What destination MAC address would be included in a frame sent from a source device to a destination device on the same local network?

The MAC address of the destination device.

What destination MAC address would be included in a frame sent from a source device to a destination device on a remote local network?

The MAC address of the local router interface.

ARP - Step 1

The sending host creates and sends a frame addressed to a broadcast MAC address. Contained in the frame is a message with the IPv4 address of the intended destination host.

ARP - Step 3

The sending host receives the message and stores the MAC address and IPv4 address information in a table called an ARP table.

Physical Address (The MAC address)

Used for NIC-to-NIC communications on the same Ethernet network.

Logical Address (The IP address)

Used to send the packet from the source device to the destination device. The destination IP address may be on the same IP network as the source, or it may be on a remote network

ARP Request

a broadcast, so all devices on the same network will receive it

Ethernet Broadcast

is when the destination MAC address is 48 one-bits, or in hexadecimal, all Fs of an ethernet frame. The Ethernet frame is sent from the source to the switch which forwards(or floods) all ports except the incoming port. The results is, all devices in the network will receive the broadcast

Address Resolution Protocol (ARP)

to determine the MAC address that corresponds to a particular IP address.