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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.

1 2 ... 157 158 159 160 161 162 163 164 165 166 167 ... 211 212

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ZyXEL Communications ES-3024 Guía de usuario Pagina 162