ARP Cache

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To keep the number of broadcasted ARP Request frames to a minimum, many TCP/IP protocol stacks incorporate an ARP cache , a table of recently resolved IP addresses and their corresponding MAC addresses. The ARP cache is checked first before sending an ARP Request frame. Each interface has its own ARP cache.

Depending on the vendor implementation, the ARP cache can have the following qualities:

  • ARP cache entries can be dynamic (based on ARP Replies) or static. Static ARP entries are permanent and are manually added using a TCP/IP utility such as the ARP utility provided with Windows 2000. Static ARP cache entries are used to prevent ARP Requests for commonly-used local IP addresses, such as routers and servers. The problem with static ARP entries is that they have to be manually updated when network interface equipment changes.

  • Dynamic ARP cache entries have a time-out value associated with them to remove entries in the cache after a specified period of time. Dynamic ARP cache entries for Windows 2000 TCP/IP are given a maximum time of 10 minutes before being removed.

To view the ARP cache on a Windows 2000–based computer, type arp -a at a Windows 2000 command prompt.