TCP/IP Tutorial and Technical Overview - IBM Redbooks

An exception to the rule is the asynchronous transfer mode (ATM) technology,
where ARP cannot be implemented in the physical layer as described previously.
Therefore, every host, upon initialization, must register with an ARP server in
order to be able to resolve IP addresses to hardware addresses (also see 2.10,
“Asynchronous transfer mode (ATM)” on page 47).
ARP was designed to be used on networks that support hardware broadcast.
This means, for example, that ARP will not work on an X.25 network.
3.4.2 ARP detailed concept
ARP is used on IEEE 802 networks as well as on the older DIX Ethernet
networks to map IP addresses to physical hardware addresses (see 2.1,
“Ethernet and IEEE 802 local area networks (LANs)” on page 30). To do this, it is
closely related to the device driver for that network. In fact, the ARP
specifications in RFC 826 only describe its functionality, not its implementation.
The implementation depends to a large extent on the device driver for a network
type and they are usually coded together in the adapter microcode.
ARP packet generation
If an application wants to send data to a certain IP destination address, the IP
routing mechanism first determines the IP address of the next hop of the packet
(it can be the destination host itself, or a router) and the hardware device on
which it should be sent. If it is an IEEE 802.3/4/5 network, the ARP module must
be consulted to map the to a physical
address.
The ARP module tries to find the address in this ARP cache. If it finds the
matching pair, it gives the corresponding 48-bit physical address back to the
caller (the device driver), which then transmits the packet. If it does not find the
pair in its table, it discards the packet (the assumption is that a higher-level
protocol will retransmit) and generates a network broadcast of an ARP request.
See Figure 3-39 on page 121 for more details.
120 TCP/IP Tutorial and Technical Overview