Address Resolution - Bay Networks NauticaRS Reference Manual

NauticaRS 5.5R Reference Guide

Address Resolution

1-14
An IP address alone cannot be used to deliver data to another
device on a LAN. To send data to another point on the network,
the IP address must be converted to a unique identifier for the
destination device on an Ethernet LAN. Each device on an
Ethernet LAN has a unique Ethernet MAC (Media Access
Control) address. This is a 48-bit number, usually assigned by the
manufacturer. Some devices may have more than one MAC
address for multiple connections to Ethernet networks.
Converting an IP address to a matching MAC address is called
address resolution. Unless the router can resolve the network IP
address to the Ethernet MAC address, it cannot send the data
explicitly to the correct device on the LAN. IP uses Address
Resolution Protocol (ARP) to do this.
ARP is used if a device needs to send data to another station on
the network and it does not know the destination MAC address.
An ARP request is broadcast to all stations on the network. The
destination IP address for the desired station is included as part of
the message, so that only the station with this IP address responds
to the ARP request and all others discard it. The node whose IP
address was in the ARP request responds directly to the sender
with its own MAC address. This gives the sender the destination
MAC address needed to send the data.
The IP and MAC address data for each node is held in a host
cache or ARP table, so that the next time data needs to be sent, the
address can be obtained from the address information in the ARP
table.
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