ARP.exe

ARP - Address Resolution Protocol.

Display and modify the IP-to-Physical address translation tables used by address resolution protocol.

Syntax
   View the contents of the local ARP cache table 
      ARP -a [ip_addr] [-N if_addr] -v

   Add a static Arp entry for frequent accessed hosts 
      ARP -s ip_addr eth_addr [if_addr]

   Delete an entry 
      ARP -d ip_addr [if_addr]

Key
   -a           Display current ARP entries.
                Can include more than one network interface.
                If ip_addr is specified, the IP and Physical
                addresses for only the specified computer are displayed.

   -g           Same as -a.

   -N if_addr   Display the ARP entries for the network interface specified
                by if_addr. This parameter is case-sensitive.

   -d ip_addr   Delete the host specified by ip_addr.
                -d *  will delete all entries.

   -s           Add the host and associates the Internet address ip_addr
                with the Physical address eth_addr.  Optionally, specify if_addr to add the entry
                to a specific interface.
                The entry is permanent until the TCP/IP stack is restarted.

   eth_addr     Specifies a physical address. The format is six hex bytes separated by hyphens.

   if_addr      If present, this specifies the Internet address of the
                interface whose address translation table should be modified.
                If not present, the first applicable interface will be used.

   -v 	     Display ARP entries in verbose mode, including additional details
               such as invalid entries and entries on the loopback interface.

If two hosts on the same sub-net cannot ping each other successfully, try running ARP -a to list the addresses on each computer to see if they have the correct MAC addresses.

A host’s MAC address can be checked using IPCONFIG. If another host with a duplicate IP address exists on the network, the ARP cache might have had the MAC address for the other computer placed in it. ARP -d is used to delete an entry that is incorrect.

Examples

Display the ARP cache tables for all interfaces:

C:\> arp -a

Display the ARP cache table for the interface on IP address 10.1.4.99:

C:\> arp -a -N 10.1.4.99

Add a static ARP cache entry on IP addr 10.1.4.77 to the physical address 00-AA-21-4A-2F-9A:

C:\> arp -s 10.1.4.77 00-AA-21-4A-2F-9A

“One resolution I have made, and try always to keep, is this: To rise above little things” ~ John Burroughs

Related commands

ROUTE - Manipulate network routing tables.
MacOS equivalent: arp