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90.1 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.
90.1.1 How ARP Works
When an incoming packet destined for a host device on a local area network arrives at the OLT, the
OLT's ARP program looks in the ARP Table and if it finds the address, it 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 OLT
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 OLT 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.
90.2 ARP Commands
The following section lists the commands for this feature.
Table 342 ARP Commands
COMMAND
show ip arp
clear ip arp
clear ip arp interface port-channel
<aid>
clear ip arp ip <ip-address>
no arp
C
DESCRIPTION
Displays the ARP table.
Removes all of the dynamic entries from the ARP
table.
Removes the dynamic entries learned on the
specified port.
aid: <msc|ge|pon>-<slot>-<port>
Removes the dynamic entries learned with the
specified IP address.
Flushes the ARP table entries.
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