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The ArpCacheLife and ArpCacheMinReferencedLife registry entries determine how the ARP cache is maintained in Windows XP and in Windows Server 2003. These registry entries no longer apply to Windows Vista.

In the new Windows Vista TCP/IP stack implementation, hosts create the neighbor cache entries when there is no matching entry in the neighbor cache. ARP cache entry for IPv4 is an example of a neighbor cache entry. After the entry is successfully created in the neighbor cache, the entry may change to the Reachable state if the entry meets certain conditions. If the entry is in the Reachable state, Windows Vista TCP/IP hosts do not send ARP requests to the network. Therefore, Windows Vista TCP/IP hosts do not use the information in the cache. If entry is not used and stays in the Reachable state for longer than its Reachable Time value, the entry changes to the Stale state. If an entry is in the Stale state, the Windows Vista TCP/IP host must send an ARP request to reach that destination.

The Reachable Time value is calculated as follows:

RFC provides the following calculated results.

Therefore, the Reachable Time value is somewhere between 15 seconds (30 × 0.5 seconds) and 45 seconds (30 × 1.5 seconds). If an entry is not used for a time between 15 to 45 seconds, it changes to the Stale state. Then, the host must send an ARP Request for IPV4 to the network when any IP datagram is sent to that destination.

To see the current Reachable Time value, follow these steps:

Idx  Met   MTU   State        Name---  ---  -----  -----------  -------------------  1   50 4294967295  connected    Loopback Pseudo-Interface 1  9   20   1500  connected    Local Area Connection

Interface Local Area Connection Parameters----------------------------------------------IfLuid                             : ethernet_7IfIndex                            : 9Compartment Id                     : 1State                              : connectedMetric                             : 20Link MTU                           : 1500 bytesReachable Time                     : 19000 ms Base Reachable Time : 30000 ms Retransmission Interval : 1000 ms				DAD Transmits : 3 Site Prefix Length : 64 Site Id : 1 Forwarding : disabled				Advertising : disabled Neighbor Discovery : enabled Neighbor Unreachability				Detecion : enabled Router Discovery : dhcp Managed Address Configuration :				enabled Other Stateful Configuration : enabled Weak Host Sends : disabled Weak				Host Receives : disabled Use Automatic Metric : enabled Ignore Default routes :				disabled 

Interface Local Area Connection Parameters----------------------------------------------IfLuid                             : ethernet_7IfIndex                            : 9Compartment Id                     : 1State                              : connectedMetric                             : 20Link MTU                           : 1500 bytesReachable Time                     : 61500 msBase Reachable Time                : 60000 ms Retransmission Interval : 1000 ms DAD Transmits : 3 Site Prefix				Length : 64 Site Id : 1 Forwarding : disabled Advertising : disabled Neighbor				Discovery : enabled Neighbor Unreachability Detecion : enabled Router Discovery				: dhcp Managed Address Configuration : enabled Other Stateful Configuration :				enabled Weak Host Sends : disabled Weak Host Receives : disabled Use Automatic				Metric : enabled Ignore Default routes : disabled 

For more information about the neighbor cache entry states, visit the following Web site:

For more information about TCP/IP registry values for Windows Vista and for Windows Server 2008, visit the following Web site:

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