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2007/09/03 Tweak DNS Errors Caching in Windows 2000 / XP

2007/09/03 15:35

Tweak DNS Errors Caching in Windows 2000 / XP

2007/09/03 15:35 in MS Windows Tweak

Windows 2000/XP has built-in DNS (Domain Name System) caching, which basically caches resolved hostnames for faster access and reduced DNS lookups. This is generally a great feature, with the only downside that failed DNS lookups get cached by default as well... When a DNS lookup fails (due to temporary DNS problems), Windows still caches the unsuccessful DNS query, and in turn fails to connect to a host regardless of the fact that the DNS server might be able to handle your lookup seconds later.

There are a couple of different ways to tweak Windows 2k/XP not to cache failed DNS lookups:

1. You can flush the DNS cache manually, by going to Command Prompt and typing: ipconfig /flushdns
2. You can wait for the cached lookup to expire or reboot the system...

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Dnscache\Parameters]

MaxNegativeCacheTtl=0 (DWORD, default value: 0x12C (300 seconds), range: 0x0–0xFFFFFFFF seconds) Description: Determines how long an entry recording a negative answer to a query remains in the DNS cache. When the time specified in the value of this entry expires, the DNS client deletes the answer record from cache. This is a Windows XP and 2003 Server setting only, the Windows 2000 equivalent is NegativeCacheTime.

NegativeCacheTime=0 (DWORD, default value: 0x12C (300 seconds), range: 0x0–0xFFFFFFFF seconds) Description: Determines how long an entry recording a negative answer to a query remains in the DNS cache. When the time specified in the value of this entry expires, the DNS client deletes the answer record from cache. This is a Windows 2000 only setting, please use the MaxNegativeCacheTtl for Windows XP and 2003 Server instead.

NetFailureCacheTime=0 (DWORD, default value: 0x1E (30 seconds), range: 0x0–0xFFFFFFFF seconds) Description: Determines for how long the DNS client stops sending queries when it suspects that the network is down. When the DNS client does not receive responses to repeated queries sent to any network adapter, the DNS client stops sending queries for the time specified in the value of this entry. During that time, the DNS client returns a timeout response to all queries. If the value of this entry is 0x0, this optimizing feature is disabled. DNS continues to send queries to an unresponsive network.

NegativeSOACacheTime=0 (DWORD. default value: 0x78 (120 secnds), range: 0x0–0xFFFFFFFF seconds) Description: Determines how long an entry recording a negative answer to a query for an SOA (Start of Authority) record remains in the Domain Name System (DNS) cache. When the time specified in the value expires, the DNS client deletes the answer record from the cache.

Note: As always when editing the Registry, a backup is a good idea, and reboot might be required for changes to take effect.

Posted by Super Coder