Windows Server 2003 adjusts the size of the ARP cache automatically to meet the needs of the system. If an entry is not used by any outgoing datagram for two minutes, the entry is removed from the ARP cache. Entries that are being referenced are removed from the ARP cache after ten minutes. Entries added manually are not removed from the cache automatically. The registry parameter ArpCacheLife, described in Appendix A, allows more administrative control over aging.
Use the command arp –d to delete entries from the cache, as shown below:
C:\>arp -d 10.0.0.32
C:\>arp -a
Interface: 157.60.137.88 --- 0x10003
Internet Address Physical Address Type
157.60.136.1 00-0a-42-b0-54-0a dynamic
157.60.137.0 00-b0-d0-e9-41-43 dynamic
Interface: 10.0.0.3 --- 0x10004
Internet Address Physical Address Type
10.0.0.1 08-00-2b-c4-25-b6 dynamic
ARP queues only one outbound IP datagram for a specified destination address while that IP address is being resolved to a MAC address. If a UDP-based application sends multiple IP datagrams to a single destination address without any pauses between them, some of the datagrams may be dropped if there is no ARP cache entry already present. An application can compensate for this by calling the Iphlpapi.dll routine SendArp() to establish an ARP cache entry, before sending the stream of packets. See INFO: IP Helper APIs Add Net Config and Stat Info to Win32 Apps or the MSDN for IP Helper API details.
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