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. 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. -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 might have had the MAC address for the other computer placed in it. ARP -d is used to delete an entry that is incorrect.
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
ROUTE - Manipulate network routing tables
Q199773 - Behaviour of Gratuitous ARP
Q140859 - Win NT TCP/IP Routing Basics