ZyXEL VMG1312-B30A User Guide - Page 249

ARP Table

Page 249 highlights

CHAPTER 22 ARP Table 22.1 Overview Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP address) to a physical machine address, also known as a Media Access Control or MAC address, on the local area network. An IP (version 4) address is 32 bits long. In an Ethernet LAN, MAC addresses are 48 bits long. The ARP Table maintains an association between each MAC address and its corresponding IP address. 22.1.1 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. 22.2 ARP Table Screen Use the ARP table to view IP-to-MAC address mapping(s). To open this screen, click System Monitor > ARP Table. Figure 122 System Monitor > ARP Table The following table describes the labels in this screen. Table 94 System Monitor > ARP Table LABEL DESCRIPTION # This is the ARP table entry number. IP Address This is the learned IP address of a device connected to a port. VMG1312-B Series User's Guide 249

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VMG1312-B Series User’s Guide
249
C
HAPTER
22
ARP Table
22.1
Overview
Address Resolution Protocol (ARP) is a protocol for mapping an Internet Protocol address (IP
address) to a physical machine address, also known as a Media Access Control or MAC address, on
the local area network.
An IP (version 4) address is 32 bits long. In an Ethernet LAN, MAC addresses are 48 bits long. The
ARP Table maintains an association between each MAC address and its corresponding IP address.
22.1.1
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.
22.2
ARP Table Screen
Use the ARP table to view IP-to-MAC address mapping(s). To open this screen, click
System
Monitor
>
ARP Table
.
Figure 122
System Monitor > ARP Table
The following table describes the labels in this screen.
Table 94
System Monitor > ARP Table
LABEL
DESCRIPTION
#
This is the ARP table entry number.
IP Address
This is the learned IP address of a device connected to a port.