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6.2 Establish Address Resolution
A device in the IP can have both a local address (which uniquely identifies the device on its local segment or LAN)
and a network address (which identifies the network to which the device belongs). The local address is more properly
known as a data link address because it is contained in the data link layer (Layer 2 of the OSI model) part of the
packet header and is read by data link devices (bridges and all device interfaces, for example). The more technically
inclined will refer to local addresses as MAC addresses, because the Media Access Control (MAC) sub-layer within
the data link layer processes addresses for the layer.
To communicate with a device on Ethernet, you first must determine the 48-bit MAC or local data link address of that
device. The process of determining the local data link address from an IP address is called address resolution. The
IntraCore IC36240 software uses the Address Resolution Protocol (ARP) for address resolution. ARP is used to
associate IP addresses with media or MAC addresses. Taking an IP address as input, ARP determines the
associated media address.
Once a media or MAC address is determined, the IP address/media address association is stored in an ARP cache
for rapid retrieval. Then the IP datagram is encapsulated in a link-layer frame and sent over the network.
6.2.1 Define a Static ARP Cache
ARP provides a dynamic mapping between IP addresses and media addresses. Because most hosts support
dynamic address resolution, you generally do not need to specify static ARP cache entries. Completing this task
installs a permanent entry in the ARP cache. The entry is used to translate 32-bit IP addresses into 48-bit hardware
addresses.
Optionally, you can specify that the software respond to ARP requests as if it was the owner of the specified IP
address. You also have the option of specifying an interface when you define ARP entries.
Perform the following task in global configuration mode, to provide static mapping between IP addresses and media
addresses.
Command Purpose
arp ip-address hardware-address
Globally associate an IP address with a media (hardware)
address in the ARP cache.
arp ip-address hardware-address
[interface ]
Specify that the software respond to ARP requests as if it
was the owner of the specified interface.
To display the ARP being used on a particular interface, use the show interface in top mode or global configuration
mode. Use the show arp command in top or configuration mode to examine the contents of the ARP cache.
55 Asante IntraCore IC36240 User’s Manual