DNS name cache behavior of ISA Server Web Proxy (301695)


The information in this article applies to:

  • Microsoft Internet Security and Acceleration Server 2000
  • Microsoft Small Business Server 2000
This article was previously published under Q301695
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256986 Description of the Microsoft Windows Registry

SYMPTOMS

The ISA Web Proxy service caches name resolution responses from DNS servers (or other means such as a HOSTS file) for a default time of 6 hours. However, the ipconfig /flushdns command does not flush this cached entry because it is saved inside the Web Proxy service.

RESOLUTION

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To work around this behavior, note that the TTL that is used for caching DNS responses is controlled by the following registry entry that you can change to a smaller value:

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Fpc\Arrays\{ARRAYGUID}\ArrayPolicy\WebProxy

"msFPCDnsCacheTtl"=dword:00005460

The value is in seconds that are represented in hexadecimal, and the number that is shown is: 0x5460 = 21600 = 6 hrs

The following {ARRAYGUID} value will be a number like this number:

{32E328DE-7C4E-47F8-B1AB-A7891AAC98A7}

NOTE: The default TTL for DNS records is 1 hour, and the Web Proxy service should be restarted for it to read the new value.

For Enterprise Arrays, the following value must be modified in Active Directory
The attribute in AD is "msfpcDnsCacheTtl" at: CN=WebProxy,CN=ArrayPolicy,CN={ArrayGUID},CN=Arrays,CN=Fpc,CN=System,DC=Vanguard,DC=Com

Note The "msfpcDnsCacheTtl" value in AD is in seconds, where the default value for the "msfpcDnsCacheTtl" attribute should be shown as 21600 (21600sec =6hr)

Note This article does not apply to ISA Server 2004. ISA Server 2004 does not use the "msFPCDnsCacheTtl" value. Instead ISA Server uses the TTL value that is defined on the DNS record.
Modification Type:MinorLast Reviewed:1/19/2005
Keywords:kbenv kbprb KB301695
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