Appletalk Address Resolution Protocol (Aarp) Cache - 3Com corebuilder 3500 Implementation Manual

462 C 16: A
HAPTER PPLE
AppleTalk Address
Resolution Protocol
(AARP) Cache
T
ALK
The AppleTalk Address Resolution Protocol (AARP) maps the hardware
address of an AppleTalk node to an AppleTalk protocol address. AARP
maps for both extended and nonextended networks.
Your system uses AppleTalk Address Resolution Protocol (AARP) to map
hardware addresses to AppleTalk protocol addresses. AppleTalk protocol
uses dynamically assigned 24-bit addresses.
AppleTalk addresses are 24 bits long and consist of a 16-bit network
number and a unique 8-bit node number. AppleTalk networks support a
hierarchal addressing scheme in the form of a network range, with each
16-bit network number within that range capable of supporting up to
254 nodes.
All AppleTalk nodes, including router interfaces, dynamically acquire a
unique AppleTalk address using a feature provided by the AppleTalk
Address Resolution protocol, called Probe.
When a node on the network initializes, it randomly selects an AppleTalk
address for itself. At the same time, the node sends 10 AARP probe
packets. The probe packets determine whether any other nodes on the
network are using the selected address. If the address already exists, the
initializing node randomly selects another address and sends another set
of probe packets.
The AARP maintains an Address Mapping Table (AMT) with the most
recently used hardware addresses and their corresponding AARP
addresses. If an address is not in this table, the router broadcasts AARP
requests to all other AppleTalk nodes on the link to determine the MAC
address mapping for the specified AARP address. It then creates a
corresponding AMT entry to reflect the new mapping when the
destination node replies. You view this table, called the AARP cache,
through the Administration Console.
AARP uses an Address Mapping Table (AMT), which contains the most
recently used addresses. If an address is not in the AMT, the system sends
an AARP request to the designated protocol address and then adds the
node's destination hardware address to the table when the node replies.