
Configuring IP Services
5-2 117356-A Rev. A
ARP Overview
The IP router needs both a physical address and an IP address to transmit a
datagram. In situations where the router knows only the network host’s IP address,
the Address Resolution Protocol (ARP) enables the router to determine a network
host’s physical address by binding a 32-bit IP address to a 48-bit MAC address. A
router can use ARP across a single network only, and the network hardware must
support physical broadcasts.
For example, in Figure 5-
1, the router and Host C are on the same physical
network. Both devices have an assigned IP address (the router’s is 140.250.200.1
and Host C’s is 140.250.200.4) and both devices have an assigned physical
address (the router’s is 00 00 A2 00 00 01 and Host C’s is 00 00 A2 00 10 40).
Figure 5-1. ARP Example
140.250.200.0
140.250.200.1
00 00 A2 00 00 01
140.250.200.2
00 00 A2 00 10 20
140.250.200.3
00 00 A2 00 10 30
140.250.200.4
00 00 A2 00 10 40
Router
Host
C
Host
A
Host
B
IP0010A
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