Manage DNS Client Cache in Windows 2000 pro

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Manage the DNS Client Cache in Windows 2000 pro
Manage DNS Client caching in Windows 2000 pro

By Jim Boyce
Author: Purple endurer
Keywords: Windows 2000 | Microsoft Windows | Domain Names
Keyword: Windows 2000 | Microsoft Windows | Domain Name

 

Takeaway:
If a lookup fails for a host because the target domain's DNS server is down, then subsequent attempts to look up the host will also fail because the failed results are cached. learn two ways to overcome this problem.
Overview:
If a host fails to be queried because the DNS server responsible for its domain name resolution is disabled, subsequent queries to this host will also fail due to (previous) failed results are cached and fail. Let's learn two ways to overcome this problem.

 

DNS enables fully qualified host names like www.techrepublic.com to be resolved to their target IP addresses. every time you visit a Web site, the DNS Client software built into Windows 2000 Professional performs a DNS lookup of the specified host name to obtain the IP address of the target server.
DNS can resolve a fully valid host name such as www.techrepublic.com to the target IP address. Each time you access a website, the DNS Client software built into Windows 2000 Professional executes a query of the specified host name to obtain the IP address of the target server.

The DNS client caches the results of each Name Lookup to speed up subsequent requests for the address. the default cache timeout is 30 minutes. if a lookup result is longer than 30 minutes, Windows performs an external lookup of the host and refreshes the cached copy.
Each name cached by the DNS client to accelerate Subsequent Address requests. The default cache duration is 30 minutes. If a query result is longer than 30 minutes, Windows executes a host extension query and refreshes the cache copy.

Although caching can improve name resolution performance, it can also affect resolution in a negative way. in addition to caching positive results, windows also caches negative results. so, if a lookup fails for a host because the target domain's DNS server is down, then subsequent attempts to look up the host will also fail because the failed results are cached. you can overcome this problem in one of two ways: flush the DNS Cache and try again when the server comes back on line, or change the cache timeout.
Although the cache can improve the name resolution performance, it can also negatively affect resolution. In addition to caching valid results, windows also caches bad results. Therefore, if the query for a host fails because the DNS server responsible for its domain name resolution is disabled, the subsequent query for this host will also be due to (previous) failed results are cached and fail. You can use either of the following methods to overcome this problem: refresh the DNS Cache and try again when the server goes online again, or modify the cache duration.

To change cache timeout, open the Registry Editor and add the DWORD Value
To modify the cache duration, open the Registry Editor and add the DWORD Value:

HKEY_CURRENT_USER/software/Microsoft/Windows/CurrentVersion/Internet Settings/dnscachetimeout.

Set the value of dnscachetimeout to the number of seconds you want entries to be cached.
Set the dnscachetimeout value in seconds as you want.

To flush the DNS Cache altogether, use the following command at a console prompt:
To refresh the DNS cache, run the following command on the command console:

Ipconfig/flushdns

Note: editing the registry is risky, so be sure you have a verified backup before saving any changes.