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GS-1524/GS-1548 User’s Guide
137
CHAPTER 20
Dynamic ARP
This chapter describes how to activate dynamic Address Resolution Protocol (ARP)
learning and how to enter static ARP table entries.
20.1 ARP Table Overview
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.
20.1.1 ARP Table Entries
The ARP table is populated with MAC and corresponding IP address mappings in
two different ways.
• DHCP Snooping - The Switch listens to traffic from a DHCP server on a trusted
port and learns IP-to-MAC address bindings by parsing DHCP ACK packets.
• Static Entries - The Switch administrator can enter static IP-to-MAC address
mappings via the web configurator.
20.1.2 How Dynamic ARP Works
When an incoming ARP 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, dynamic ARP discards the ARP packet.