Arp Table; Arp Table Overview; How Arp Works - ZyXEL Communications Nebula LTE3301-PLUS User Manual

23.1 ARP Table Overview

Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol (IP) address to a
physical machine address, known as a Media Access Control (MAC) address, on the local area
network.
An IP version 4 address is 32 bits long. MAC addresses are 48 bits long. The ARP table maintains an
association between each MAC address and its corresponding IP address.

23.1.1 How ARP Works

When an incoming packet destined for a host device on a local area network arrives at the device, the
device's ARP program looks in the ARP table and, if it finds the address, sends it to the device.
If no entry is found for the IP address, ARP broadcasts the request to all the devices on the LAN. The
device fills in its own MAC and IP address in the sender address fields, and puts the known IP address of
the target in the target IP address field. In addition, the device puts all ones in the target MAC field
(FF.FF.FF.FF.FF.FF is the Ethernet broadcast address). The replying device (which is either the IP address of
the device being sought or the router that knows the way) replaces the broadcast address with the
target's MAC address, swaps the sender and target pairs, and unicasts the answer directly back to the
requesting machine. ARP updates the ARP table for future reference and then sends the packet to the
MAC address that replied.

23.2 ARP Table

Use the ARP table to view the IPv4-to-MAC address mappings for each device connected to the Zyxel
Device. The neighbor table shows the IPv6-to-MAC address mappings of each IPv6 neighbor. To open
this screen, click System Monitor > ARP Table.
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