Zyxel OLT2412 [257/326] Arp table

Zyxel OLT2412 [257/326] Arp table
OLT2412 User’s Guide 257
CHAPTER 36
ARP Table
This chapter introduces ARP Table.
36.1 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.
36.1.1 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.
36.2 ARP Commands
The following section lists the commands for this feature.
Table 144 ARP Commands
COMMAND DESCRIPTION
show ip arp
Displays the ARP table.
clear ip arp
Removes all of the dynamic entries from the ARP table.
clear ip arp interface port-
channel <aid>
Removes the dynamic entries learned on the specified port.
aid: <xe|ge|pon>-<slot>-<port>
clear ip arp ip <ip-address>
Removes the dynamic entries learned with the specified IP
address.
no arp
Flushes the ARP table entries.

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