ZyXEL Communications Dimension ES-3024, User Manual, Page: 162 / 212

Dimension ES-3024 Ethernet Switch
ARP Table 24-1
Chapter 24
ARP Table
This chapter introduces ARP Table.
24.1 Introduction to ARP Table
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.
24.1.1 How ARP Works
When an incoming packet destined for a host device on a local area network arrives at the switch, the switch'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 switch 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 switch 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.
24.2 Viewing ARP Table
Click Management in the navigation panel and then ARP Table to open the following screen. The ARP table can
hold up to 500 entries.