Arp is a protocol used to determine host IP addresses from their physical MAC or Ethernet address. Windows operating systems provides arp command in order to manage arp related information. With arp command we can display, add and remove arp entries in ARP cache.

ARP Cache

ARP and IP entries are hold  in ARP cache every time we want to communicate over network and need IP address we look to the ARP cache. ARP cache is populated with ARP request or manually with static ARP entries

Entry Types

ARP cache have two type of entries. They are called static and dynamic .

Dynamic

Dynamic entries are populated by operating system after ARP request. The returned ARP responses are put into the ARP cache.

Static

Static entries a populated by manually where we look in detail.

List and Display ARP Entries

We can list currently available ARP entries in cache with -a option. This will list entries according to related interfaces. In this example we have two interfaces and this will create two table

Add Static ARP Entry

Another useful feature of arp command is adding static ARP entries. This will add given IP address and Mac address to the ARP cache. This entry will be stored up to computer restart . This type of entries also listed as Type static while listing entries. We will provide the IP address and the Mac address like below. We will use -s parameter.

> arp -s 192.168.122.50 00-aa-00-62-c6-09

We can see the entry as static type.

Remove ARP Entry

We can also remove existing ARP entries. The entry type can be static or dynamic . We will use -d option and the IP address of the entry we want to delete. In this example we will remove ARP entry related with IP address 192.168.122.50 .

> arp -d 192.168.122.50