3Com 4210G Series, Configuration Manual, Page: 215 / 1133

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This document is organized as follows:
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ARP Configuration
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Proxy ARP Configuration
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ARP Attack Defense Configuration
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ARP Configuration
When configuring ARP, go to these sections for information you are interested in:
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ARP Overview
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Configuring ARP
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Configuring Gratuitous ARP
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Displaying and Maintaining ARP
ARP Overview
ARP Function
The Address Resolution Protocol (ARP) is used to resolve an IP address into an Ethernet MAC
address (or physical address).
In a LAN, when a host or other network device is to send data to another host or device, the sending
host or device must know the network layer address (that is, the IP address) of the destination host or
device. Because IP datagrams must be encapsulated within Ethernet frames before they can be
transmitted over physical networks, the sending host or device also needs to know the physical
address of the destination host or device. Therefore, a mapping between the IP address and the
physical address is needed. ARP is the protocol to implement the mapping function.
ARP Message Format
Figure 2-1
ARP message format
The following explains the fields in
Figure 2-1 .
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Hardware type: This field specifies the hardware address type. The value “1” represents Ethernet.
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Protocol type: This field specifies the type of the protocol address to be mapped. The hexadecimal
value “0x0800” represents IP.
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Hardware address length and protocol address length: They respectively specify the length of a
hardware address and a protocol address, in bytes. For an Ethernet address, the value of the