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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

1 2 ... 76 77 78 79 80 81 82 83 84 85 86 ... 173 174

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