DNS Caching problem

[JohnH]

Hi,
I have following problem. Our company has many wide
locations (shops) connected to central through slow (about
128 Kbps) and unstable links. At each location is DNS
server, configured as caching-only for limiting
replication traffic (root hints includes main DNS server
in company). Clients are using cached records and
everything works fine. Problem occurs when data link goes
down and clients need to connect at least to each other
and to server. After some time cached records disappear
from local/server cache. There is maximum time to live
limit for cached record, which is in default one day and
which can be changed by MaxCacheTtl key in registry.
Problem is that cache records have mostly only 20 minutes
Ttl (in the beginning) and after 20 min clients can´t get
anywhere. Is it normal if MaxCacheTtl key is set to one
day? Is MaxCacheTtl setting also minimum Ttl or just
maximum - is there some key which sets minimum Ttl?
Network failure may last several hours, so I need to have
minimum Ttl longer than 20 minutes.

Thanks a lot and sorry for my english (hope you will
understand

 

[Ace Fekay [MVP]]

Hi John,

Your English is fine.

My best suggestion, due to the unreliable links, is to create secondary
zones on each DNS server at these locations. Caching servers are usually
recommended in a scenario where there are reliable links.

Is this an AD infrastructure?
If so, is there a DC at each location?

--
Regards,
Ace

Please direct all replies to the newsgroup so all can benefit.
This posting is provided "AS IS" with no warranties.

Ace Fekay, MCSE 2000, MCSE+I, MCSA, MCT, MVP
Microsoft Windows MVP - Active Directory
--
=================================

Hi,
I have following problem. Our company has many wide
locations (shops) connected to central through slow (about
128 Kbps) and unstable links. At each location is DNS
server, configured as caching-only for limiting
replication traffic (root hints includes main DNS server
in company). Clients are using cached records and
everything works fine. Problem occurs when data link goes
down and clients need to connect at least to each other
and to server. After some time cached records disappear
from local/server cache. There is maximum time to live
limit for cached record, which is in default one day and
which can be changed by MaxCacheTtl key in registry.
Problem is that cache records have mostly only 20 minutes
Ttl (in the beginning) and after 20 min clients can´t get
anywhere. Is it normal if MaxCacheTtl key is set to one
day? Is MaxCacheTtl setting also minimum Ttl or just
maximum - is there some key which sets minimum Ttl?
Network failure may last several hours, so I need to have
minimum Ttl longer than 20 minutes.

Thanks a lot and sorry for my english (hope you will
understand

 

[Guest]

Thanks,
I have already done it on test server, where I can
simulate network failure and it works fine.
Yes, its AD infrastructure and there is a DC on each
server. Without that it would be impossible to logon and
access resources on the server when link goes down.

 

[Ace Fekay [MVP]]

In

Thanks,
I have already done it on test server, where I can
simulate network failure and it works fine.
Yes, its AD infrastructure and there is a DC on each
server. Without that it would be impossible to logon and
access resources on the server when link goes down.

If y ou have DCs at each location, and they are part of the same domain, I
would suggest to make the zones AD Integrated and not use Caching servers.
This will ensure logons when the links go down. Even if you have DCs, but
are using Caching only servers, there is still a chance that logons may not
work because the logon process requires DNS.


--
Regards,
Ace

Please direct all replies to the newsgroup so all can benefit.
This posting is provided "AS IS" with no warranties.

Ace Fekay, MCSE 2000, MCSE+I, MCSA, MCT, MVP
Microsoft Windows MVP - Active Directory