NETGEAR GS748T - Configuring ARP

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GS748T Smart Switch
Configuring ARP
The address resolution protocol (ARP) associates a layer 2 MAC address with a layer 3 IPv4
address. GS748T Smart Switch software features both dynamic and manual ARP
configuration. With manual ARP configuration, you can statically add entries into the ARP
table.
ARP is a necessary part of the internet protocol (IP) and is used to translate an IP address to
a media (MAC) address, defined by a local area network (LAN) such as Ethernet. A station
needing to send an IP packet must learn the MAC address of the IP destination, or of the next
hop router, if the destination is not on the same subnet. This is achieved by broadcasting an
ARP request packet, to which the intended recipient responds by unicasting an ARP reply
containing its MAC address. Once learned, the MAC address is used in the destination
address field of the layer 2 header prepended to the IP packet.
The ARP cache is a table maintained locally in each station on a network. ARP cache entries
are learned by examining the source information in the ARP packet payload fields, regardless
of whether it is an ARP request or response. Thus, when an ARP request is broadcast to all
stations on a LAN segment or virtual LAN (VLAN), every recipient has the opportunity to store
the sender’s IP and MAC address in their respective ARP cache. The ARP response, being
unicast, is normally seen only by the requestor, who stores the sender information in its ARP
cache. Newer information always replaces existing content in the ARP cache.
The GS748T switches support 1024 ARP entries, which includes dynamic and static ARP
entries.
Devices can be moved in a network, which means the IP address that was at one time
associated with a certain MAC address is now found using a different MAC, or may have
disappeared from the network altogether (i.e., it has been reconfigured, disconnected, or
powered off). This leads to stale information in the ARP cache unless entries are updated in
reaction to new information seen on the network, periodically refreshed to determine if an
address still exists, or removed from the cache if the entry has not been identified as a sender
of an ARP packet during the course of an ageout interval, usually specified via configuration.
Use the following web pages to configure and display ARP detail:
• ARP Cache on page 141
• ARP Create on page 143
• Global ARP Configuration on page 142
• ARP Entry Management on page 144