Allied Telesis AT-S63 - Manual (Page 555)

AT-S63 Management Software Command Line Interface User’s Guide
Section VII: Internet Protocol Routing 555
Address
Resolution
Protocol (ARP)
Table
The switch maintains an ARP table of IP addresses and the matching
Ethernet MAC addresses. It refers to the table when routing packets to
determine the destination MAC addresses of the nodes, as well as
interfaces and ports from where the nodes are reached.
The ARP table can store both static and dynamic entries. Static entries are
entries you add yourself. This type of entry is never removed by the switch
from the ARP table, even when the corresponding nodes are inactive.
Dynamic entries are entries that the switch learns on it own. Dynamic
entries of inactive nodes are periodically removed from table to prevent the
table from filling with entries of inactive nodes.
The switch adds a dynamic entry to the table when it receives a response
to an ARP request. The switch generates an ARP request when it receives
a packet that needs to be routed across a subnet, but lacks the destination
MAC address in its ARP table. 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 until the switch receives a respond to its
ARP request, it discards all packets intended to that destination node.
The switch will also add a dynamic entry when it is the destination of an
ARP request from another node, such as when 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 for hosts which
are no longer active. Old entries are deleted. 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 commands for managing the ARP table are “ADD IP ARP” on
page 568, “DELETE IP ARP” on page 576, “SET IP ARP” on page 581,
“SET IP ARP TIMEOUT” on page 582, and “SHOW IP ARP” on page 590.
Note
The switch does not support Proxy ARP.
The storage capacity of the ARP table in an AT-9400 Series switch is:
ˆ 1024 static entries
ˆ 1024 dynamic entries