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MSAP2000 AAMS User's Guide
This chapter introduces the ARP table.
23.1 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.
23.1.1 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.
23.2 Viewing the ARP Table
Click Management in the navigation panel and then ARP Table to open the
following screen.
C
H A P T E R
ARP Table
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