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JSI Tip 1336. Can't communicate for up 10 minutes if MAC address changes.

Some devices have a fail-over capability that changes the MAC (Media Access Control) address. If this device does not update the ArpCache throughout the network, you may be unable to communicate with the device for up to 10 minutes.

Windows NT has an ArpCacheLife registry entry that controls the ArpCache life for entries that are NOT being referenced. Entries that are being referenced have a non-configurable life of 10 minutes.

Starting with SP4, a new entry, ArpCacheMinReferencedLife, is available at:


Both ArpCacheLife and ArpCacheMinReferencedLife are tpye REG_DWORD values and have a range of 0 - 0xffffffff seconds.

ArpCacheLife has a default of 120 seconds (hex 0x78) for unreferenced entries.

ArpCacheMinReferencedLife has a default of 600 seconds (hex 0x258) and controls the referenced ArpCache life as follows:

If ArpCacheLife >= ArpCacheMinReferencedLife, referenced and unreferenced arpcache entries will expire in ArpCacheLife seconds.

If ArpCacheLife < ArpCacheMinReferencedLife, unreferenced entries will expire in ArpCacheLife seconds, and referenced entries will expire in ArpCacheMinReferencedLife seconds.

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