ZyXEL Communications GS2200 Series, User Manual

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GS2200 Series User’s Guide
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H A P T E R
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ARP Table
40.1 Overview
This chapter introduces 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.
40.1.1 What You Can Do
Use the ARP Table screen ( Section 40.2 on page 293 ) to view IP-to-MAC address mapping(s).
40.1.2 What You Need to Know
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.
40.2 Viewing the ARP Table
Use the ARP table to view IP-to-MAC address mapping(s) and remove specific dynamic ARP entries.