Address Resolution Protocol (Arp) - 3Com corebuilder 3500 Implementation Manual

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Address Resolution

Protocol (ARP)

ARP is a low-level protocol that locates the MAC address that

corresponds to a given IP address. This protocol allows a host or router to

use IP addresses to make routing decisions while it uses MAC addresses

to forward packets from one hop to the next.

You do not need to implement ARP — your system has ARP capability

built in, but you can manipulate and display the contents of the ARP

When the host or router knows the IP address of the next hop towards

the packet destination, the host or router translates that IP address into a

MAC address before sending the packet. To perform this translation, the

host or router first searches its ARP cache, which is a table of IP addresses

with their corresponding MAC addresses. Each device that participates in

IP routing maintains an ARP cache. See Figure 53.

Figure 53 Example of an ARP Cache

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If the IP address does not have a corresponding MAC address, the host or

router broadcasts an ARP request packet to all the devices on the

network. The ARP request contains information about the target and

source addresses for the protocol (IP addresses). See Figure 54.