Allied Telesis AT-8100 Series - Manual (Page 1821)

AT-8100 Switch Command Line User’s Guide
1821
Address Resolution Protocol (ARP) Table
The switch has an ARP table. The switch uses the table to store the IP
addresses and Ethernet MAC addresses of the network devices. It refers
to the table to determine the destination MAC addresses of the nodes, as
well as the VLANs and ports from where the nodes are reached.
The ARP table can store both static and dynamic entries. Static entries are
entered manually. This type of entry is never removed by the switch from
the ARP table, even when the corresponding nodes are inactive.
Dynamic entries are learned by the switch itself. Dynamic entries of
inactive nodes are periodically removed from the table to prevent the table
from filling with entries of inactive nodes.
The switch learns addresses by sending out ARP requests. It generates
an ARP request when it receives a packet in which the source and
destination IP addresses are located in different networks, and the
destination MAC address is not in its ARP table. (The switch does not
send an ARP request if the source and destinations IP addresses are in
the same network.) The switch, after receiving the ARP response from the
destination node, adds the IP address and MAC address of the node to its
ARP table and begins to route packets to the device. It should be noted
that the switch, until it receives a response to its ARP request, discards all
routed packets intended for the destination node.
The switch can also learn addresses when it is the destination of an ARP
request from another node, such as when it is pinged by a management
station. The switch adds the source IP address and MAC address in the
request from the node to the table when it responds to the ARP request.
Dynamic ARP entries are aged from the table according to the ARP cache
timeout value to protect the table from filling with entries of inactive hosts.
The default setting for the timeout value is 150 seconds. This value is
adjustable with the SET IP ARP TIMEOUT command. Static ARP entries
are not aged and are retained in the table even when the nodes are
inactive.
The storage capacity of the ARP table in the switch is:
 1024 static entries
 1024 dynamic entries