D-Link DFL-2500 User Guide - Page 85
ARP Table
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66 Chapter 9. Interfaces 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
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