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]

   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.
                May 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.

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

   -s           Add the host and associates the Internet address ip_addr
                with the Physical address eth_addr.  The Physical address is
                given as 6 hexadecimal bytes separated by hyphens. The entry
                is permanent.

   eth_addr     Specifies a physical address.

   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.

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 may have had the MAC address for the other computer placed in it. ARP -d is used to delete an entry that may be 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:

ROUTE - Manipulate network routing tables
Q199773 - Behaviour of Gratuitous ARP
Q140859 - Win NT TCP/IP Routing Basics


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