New TCP/IP ArpCacheLife Parameter in Windows NT

In Windows NT 3.5 and 3.51 Service Pack 3 or earlier, an ARP cache entry times out in 2 minutes. If the same entry is used again, the time-out period is 10 minutes. The time-out entry is not user configurable.

With Windows NT version 3.51 Service Pack 4 or later, a new parameter, ArpCacheLife, allows ARP cache life to be configured.

If the new ArpCacheLife parameter is not present, the following defaults are used. Windows NT arp cache time-out defaults to 2 minutes if the entry is not used and 10 minutes if it is reused.

ArpCacheLife is found in the HKEY_LOCAL_MACHINE\SYSTEM subtree, in the following key:


ArpCacheLife determines the default lifetime in seconds for entries in the ARP cache table. Once an entry is placed in the ARP cache, it is deleted after it is allowed to remain there until its lifetime expires or until its table entry is reused because it is the oldest entry. In absence of an ArpCacheLife parameter, the default for ARP cache time-outs is a 2 minute time-out on unused entries and a 10 minute time-out on used entries.

The initial ArpCacheTable is large enough for 50 entries. When there are 50 entries, the ARP cache is allowed to grow dynamically.

This problem has been corrected in the latest Service Pack for Windows NT version 3.51 and Windows NT 4.0 or later.

Microsoft has confirmed this to be a problem in Windows NT versions 3.5 and 3.51 Service Pack 3 or earlier. This problem was corrected in Windows NT version 3.51 U.S. Service Pack 4. For information on obtaining the Service Pack, query on the following word in the Microsoft Knowledge Base (without the spaces):