VMG1312-B Series User’s Guide 251
CHAPTER 22
ARP Table
22.1 Overview
Address Resolution Prot ocol ( ARP) is a protocol for m apping an I nternet Prot ocol address ( I P
address) to a physical m achine address, also known as a Media Access Control or MAC address, on
the local area net work.
An I P (version 4) address is 32 bits long. I n an Et hernet LAN, MAC addresses are 48 bits long. The
ARP Table m aintains an associat ion between each MAC address and its corresponding I P address.
22.1.1 How ARP Works
When an incom ing packet destined for a host device on a local area netw ork arrives at the device,
the device's ARP program looks in t he ARP Table and, if it finds the address, sends it to the device.
I f no entry is found for t he I P address, ARP broadcast s t he request to all t he devices on the LAN.
The device fills in its own MAC and I P address in the sender address fields, and put s the known I P
address of t he t arget in t he t arget I P address field. I n addit ion, t he device put s all ones in t he t arget
M A C f i e l d ( FF. F F. FF. FF. FF. F F i s t h e E t h e r n e t b r o a d c a s t address). The replying device (which is either
the I P address of the device being sought or t he rout er t hat knows t he way) replaces t he broadcast
address with the t arget's MAC address, swaps t he sender and t arget pairs, and unicasts t he answer
directly back to the request ing m achine. ARP updates t he ARP Table for future reference and then
sends t he packet to the MAC address that replied.
22.2 ARP Table Screen
Use t he ARP table t o view I P- to- MAC address m apping( s). To open t his screen, click System
Monitor > ARP Table .
Figure 122 Syst em Monit or > ARP Table
The following t able describes t he labels in t his screen.
Table 94 System Monit or > ARP Table
LABEL DESCRIPTION
# This is t he ARP table ent r y num ber.
I P Address This is the learned I P address of a device connect ed to a port .
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