Address Resolution Protocol (ARP)

You can use the ARP utility to view, add, or delete entries in the ARP cache. Examples are shown below. Entries added manually are static and are not automatically removed from the cache, whereas dynamic entries are removed from the cache (see the "ARP Cache Aging" section for more information).

The arp command can be used to view the ARP cache, as shown here:

C:\>arp –a
Interface: 199.199.40.123
Internet Address Physical Address Type
199.199.40.1 00-00-0c-1a-eb-c5 dynamic
199.199.40.124 00-dd-01-07-57-15 dynamic
Interface: 10.57.8.190
Internet Address Physical Address Type
10.57.9.138 00-20-af-1d-2b-91 dynamic

The computer in this example is multihomed—has more than one NIC—so there is a separate ARP cache for each interface.

In the following example, the command arp –s is used to add a static entry to the ARP cache used by the second interface for the host whose IP address is 10.57.10.32 and whose NIC address is 00608C0E6C6A:

C:\>arp -s 10.57.10.32 00-60-8c-0e-6c-6a 10.57.8.190

C:\>arp -a

Interface: 199.199.40.123
Internet Address Physical Address Type
199.199.40.1 00-00-0c-1a-eb-c5 dynamic
199.199.40.124 00-dd-01-07-57-15 dynamic

Interface: 10.57.8.190
Internet Address Physical Address Type
10.57.9.138 00-20-af-1d-2b-91 dynamic
10.57.10.32 00-60-8c-0e-6c-6a static

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