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DNS question from DNS Noob

Posted on 2006-04-20
Medium Priority
Last Modified: 2010-04-18
I currently have a SBS 2003 server with DNS serving our internal domain and forwarding unknown domain requests to our ISP's servers. This is OK until our ISP's servers go down or have problems (yes, it has happened!). What I would like to do is implement caching on our server so that even if our ISP's DNS servers go down, we can at least have some DNS functionality (albeit out of date until the ISP DNS server comes back online)

How do I go about doing this? What are the risks?
Question by:5t34lth_G33k
  • 2
LVL 85

Expert Comment

ID: 16499325
If your ISP is unreliable, you can just remove the forwarders completely; the DNS server will then query the root DNS servers.
LVL 15

Expert Comment

ID: 16504421

oBda has the right answer here. You do not have to turn on caching - it is there by default.  If you look at the SOA record for a DNS zone - it tells the DNS servers how long the dns information should be cached, etc.

So there are no steps to "implement caching" - just use the DNS server built into Windows 2003 server.

If you use DNS Admin Console, turn on the advanced viewm then you should be able to see the cached data.

Some or many of the cached zones may only show NS record "name server" records, that simply means that only the name server records are still cached, any hosts or A record had expired.  


Author Comment

ID: 16505115
So how is it then that when our ISP's DNS servers go down, we get page cannot be displayed errors? Surely if caching is on be default, our DNS server should look to its cache when its forwarders are unavailable?
LVL 15

Accepted Solution

markpalinux earned 1500 total points
ID: 16509251

Make sure that the Root Hints tab has the root dns servers.

When you take out the forwarders your DNS server will use root hints -

example - user tries to get to www.rmhc.com 
1) the dns query is sent to your server
2) server checks its cache
3) server check for dns forwarders - none.
4) server checks the root dns server - per the root hints tab (a-m for a total of 13) to find the DNS servers "NS record" for the specific domain the dns query is for. : gets answer that name server is - ns1.rmhc.com = x.x.x.x
5) server sends query for A "host" record to ns1.rmhc.com - gets answer www=  ip address x.x.x.x
6) server caches the NS answer and the A record
7) server sends answer to the computer that sent the query

For more look at:

How DNS query works

DNS root hints reappear after being removed from in Windows Server 2003


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