DNS Cache Time 1

[acl03]

We have a Fileserver that does an automatic DNS failure to a disaster recovery if it goes down.

I am planning to reduce via a GPO or registry change or disable Client-side DNS caching on our clients. Does anyone see any issues that i should be concerned with before doing this?

I posted this in the XP forum, but i thought it maybe should have been posted here.






Thanks,
Andrew

 

[irigoyena]

Maybe its the negative DNS caching that you need to disable? client side DNS cache allows your computer to keep a list of IP addresses for Internet web sites you've successfully contacted in the last 24 hours. However, this client side cache also does something called "negative caching". The negative caching feature allows the client side cache to remember that it wasn't able to find the IP address of an Internet computer. Maybe that's where your problem is...

Disable the client side negative DNS caching

1. Click Start and point to Run. In the Run dialog box, type regedt32 in the Open text box and click OK.
2. Navigate to:
HKEY LOCAL MACHINE \ SYSTEM \ CurrentControlSet \ Services \ Dnscache \ Parameters
3. Click the Edit menu, point to New and click DWORD Value. Rename the value to NegativeCacheTime.
4. Note the default value is zero. That's exactly what you want!

Hopefully that works....

I hope you find this post helpful.

Regards,

Iggy
MCSE, MCSA:Messaging, A+, Network +

 

[acl03]

Well the problem is, the initial contact would be a successful one.

Let me try and lay it out clearly:

We have 2 servers:

Nas1 --> 10.50.0.5
Nas1dr --> 10.60.0.6

So users contact Nas1 without a problem. Then Nas1 goes down. The auto-failover makes DNS changes so that:

Nas1 --> 10.60.0.6
<null> --> 10.50.0.5

So, now in the users' cache they have Nas1-->10.50.0.5

But this doesn't exist anymore, so they can't see the DR nas box.

Make any sense?



Thanks,
Andrew

 

[irigoyena]

Yeah that makes sense...And all the users get the DNS info from a DHCP server?

Yo might just need to change the DNS cache timeout for positive responses (where a lookup was successful).

For Windows 2000 clients- Create or modify the DWORD value called "MaxCacheEntryTtlLimit".

For Windows XP and .NET Server 2003 - Create or modify the DWORD value called "MaxCacheTtl".

Set the value to equal the required timeout in seconds the default is 86400 (1 day). (are you seeing your users still being unable able to access NAS1dr after 24 hours of Nas1 going down?

To change the DNS cache timeout for negative responses (where a lookup failed).

Windows 2000 - Create or modify the DWORD value called "NegativeCacheTime".

Windows XP and .NET Server 2003 - Create or modify the DWORD value called "MaxNegativeCacheTtl".

Set the value to equal the required timeout in seconds the default is 300 (5 minutes).

Restart Windows for the changes to take effect.

You can always have the client show its DNS cache info and then have it register within DNS (if its showing incorrect info) to see if that fixes the issue. If it does, it can be a setting within your DNS servers. Not sure there though.

I hope you find this post helpful.

Regards,

Iggy
MCSE, MCSA:Messaging, A+, Network +

 

[acl03]

Well the server isn't live yet, so we haven't even gotten to try it for real yet. Just trying to fix it before it happens.



Thanks,
Andrew

 

[irigoyena]

Try doing a mock setup using two other servers/workstations to see if it works?

I hope you find this post helpful.

Regards,

Iggy
MCSE, MCSA:Messaging, A+, Network +