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ARP

Posted On 2012-03-31 by dwirch
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Tags: Networking Glossary Tutorial Windows Linux
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Display and modify the IP-to-Physical address translation tables used by address resolution protocol. 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.

Syntax


ARP -s inet_addr eth_addr [if_addr]
ARP -d inet_addr [if_addr]
ARP -a [inet_addr] [-N if_addr] [-v]

Keys


switchdescription
-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.

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

More Info


ARP stands for Address Resolution Protocol.

ARP -d is used to delete an entry that may be incorrect.

The Address Resolution Protocol is a request and reply protocol that runs encapsulated by the line protocol. It is communicated within the boundaries of a single network, never routed across internetwork nodes. This property places ARP into the Link Layer of the Internet Protocol Suite, while in the Open Systems Interconnect (OSI) model, it is often described as residing between Layers 2 and 3, being encapsulated by Layer 2 protocols. However, ARP was not developed in the OSI framework.


About the Author

dwirch has posted a total of 173 articles.

You can find more information from dwirch by visiting http://www.derekwirch.com.


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