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Periodically the ARP table is cleared of dynamic entries whose TTL has expired to ensure that the entries are current.


Static ARP table entries serve the same function as dynamic entries, but are made manually using the ARP utility.

The ARP Utility


To start the ARP utility in Windows 95/98, follow these steps:


1.    Choose Start > Programs > MS-DOS Prompt to open the MS-DOS Prompt window.


2.    At the command prompt, type ARP and any switches you need.


To start the ARP utility in Windows NT, follow these steps:


1.    Choose Start > Programs > Command Prompt to open the Command Prompt window.


2.    At the command prompt, type ARP and any switches you need.




Entered alone, the ARP command lists only the switches you must use in order to use the ARP utility correctly.


The ARP utility is primarily useful for resolving duplicate IP addresses. For example, your workstation receives its IP address from a DHCP (Dynamic Host Configuration Protocol) server, but it accidentally receives the same address as another workstation. When you try to ping it, you get no response. Your workstation is trying to determine the MAC address, and it can’t do so because two machines are reporting that they have the same IP address. To solve this problem, you can use the ARP utility to view your local ARP table and see which TCP/IP address is resolved to which MAC address. To display the entire current ARP table, use the ARP command with the -a switch, like this: ARP -a

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