User guide

Internetworking Primer A-23
Desktop Protocols
The ARP (or AARP) address mapping process is illustrated in Figure A-9 and works as
follows:
1 A node needs to deliver a packet to a network layer node address. It checks its ARP table
to determine the data link address associated with the node address. If a mapping exists,
it can deliver the packet. If a mapping does not exist, an ARP is performed.
2 To perform an ARP, the requesting node broadcasts an ARP request to all devices on the
connected network to ask who has the specific node address.
3 The device with that node address sends a unicast (a message sent to a single network
destination) ARP reply to the requesting node.
4 The requesting node adds the new mapping to its ARP table and delivers the packet.
Figure A-9 Address Resolution Protocol Mapping Process
Routing Protocols
Each network protocol has associated routing protocols that access servers and routers use
to share information about network topologies. Over time, a number of routing protocol
choices have evolved for each network protocol. Network designers should select the
routing protocol for each network protocol.
H3112
ARP request 172.16.72.1 = ?
ARP reply
172.16.72.1 = 0080.0010.1111
Router A