Arp; Arp Table - D-Link DFL-1600 User Manual

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9.6

ARP

Address Resolution Protocol (ARP) is a network protocol, which maps a
network layer protocol address to a data link layer hardware address. For
example, ARP is used to resolve IP address to the corresponding Ethernet
address. It works at the OSI Data Link Layer (Layer 2) and is encapsulated
by Ethernet headers for transmission.
A host in an Ethernet network can communicate with another host, only if
it knows the Ethernet address (MAC address) of that host. The higher
level protocols like IP uses IP addresses. These are different from the lower
level hardware addressing scheme like MAC address. ARP is used to get
the Ethernet address of a host from its IP address.
When a host needs to resolve an IP address to Ethernet address, it
broadcasts an ARP request packet. The ARP request packet contains the
source MAC address and the source IP address and the destination IP
address. Each host in the local network receives this packet. The host with
the specified destination IP address, sends an ARP reply packet to the
originating host with its MAC address.
9.6.1

ARP Table

The ARP Table is used to define static ARP entries (static binding of IP
addresses to hardware addresses) or to publish IP addresses with a specific
hardware address.
Static ARP items may help in situations where a device is reporting
incorrect hardware address in response to ARP requests. Some workstation
bridges, such as radio modems, have such problems. It may also be used to
lock an IP address to a specific hardware address for increasing security or
to avoid denial-of-service effects if there are rogue users in a network. Note
however that such a protection only applies to packets being sent to that IP
address, it does not apply to packets being sent from that IP address.
Publishing an IP address using ARP can serve two purposes:
To aid nearby network equipment responding to ARP in an incorrect
manner. This area of use is less common.
To give the impression that an interface of the firewall has more than
one IP address.
D-Link Firewalls User's Guide
Chapter 9. Interfaces