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Problems with DNS

Posted on 2004-08-26
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Last Modified: 2010-03-18
Ok, here is the situation:
We have recently had a reverse lookup added to our ISPs DNS tables to correct a problem with having our e-mails on some servers rejected as spam, we now have a problem with our client machines accessing the exchange server, they now see the external lookup and not the DNS entry on our server. We have dhcp server running giving out our server as the first point of call and the ISPs DNS server as the second. How can this machine still be trying to access the external IP address of our ISA server?

when a machine first boots up or I renew the IP address the server is clearly visible on the internal IP address, however over time the machine is resolving the host name to the external IP address. Even the DNS server will not resolve the host to the internal IP address.

The problem clearly lies with the DNS server, but how the exchange server is clearly visible with the internal IP address in the forward lookup zone for our domain.

Thanks,
Graham
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Question by:gwalker_ne8
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Expert Comment

by:adamdrayer
ID: 11902848

You should only have your machines point to your internal DNS server.  Then setup forwarding on it.  Just listing it first on the DNS server list isn't nescessariliy mean anything.

To do this, goto the DNS MMC, right-click your forward lookup zone, and goto properties.  Click on the forwarding tab and input your ISP's DNS server.  Then click ok,ok, etc..

Click "Action" -> "Clear Cache"
Then recycle your Exchange server.

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Expert Comment

by:adamdrayer
ID: 11902867
After you have done this, remove the ISP DNS server from the DHCP settings, so that the only DNS server will be the internal one.
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Expert Comment

by:adamdrayer
ID: 11902887
Sorry for the amount of posts, but you may want to first try clearing the cache and restarting the Exchange Server.  If you have Dynamic DNS, this may work.
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Author Comment

by:gwalker_ne8
ID: 11903417
Thanks Adam,

I thought as much about the machines DNS, however this was setup before I joined the company.

I've taken out the ISPs DNS from DHCP settings, added it to the forward lookup zone, cleared the cache and restarted the exchange server.

Sooner or later time will tell...
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Author Comment

by:gwalker_ne8
ID: 11903517
When I ping the exchange server host name from my DNS server it resolves it to the external address, why is this?
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Expert Comment

by:adamdrayer
ID: 11904502
no.  don't add the ISP DNS to the forward lookup zone, you have to add it to DNS forwarding in the properties of the zone!

type "nslookup <exchangeserver>"
this will resolve the name and tell you what DNS server it is using to do the resolution.

If it is using the internal DNS, then you have to check the forward lookup to see if there is an incorrect record there.  If so, delete it.  Then on the exchange server type "ipconfig /release" and then "ipconfig /renew".  Then on the box you are performing the searches, type "ipconfig /flushdns"

basically, you use nslookup to do resolution tests.  If it is using your internal server, then you have to check the forward lookup.  If it is not using your internal server, then your DNS settings are wrong or your internal server doesn't have a record for your exchange server and is forwarding the request.  In that case it seems that you are not dynamically updating the DNS server and that's a different problem.

You can always try adding a static DNS record in your forward lookup zone temporarily to see if that fixes the problem, but lets not get too far ahead of ourselves yet.

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Author Comment

by:gwalker_ne8
ID: 12004749
Sorry, I don’t understand, when I right click on our zone and go into properties I get |General | Start of Authority | Name Servers | WINS | Zone Transfers | Security |. Do you mean add the ISPs addresses into the forwarders under the server properties?

This is causing more problems now, the DNS is also the Backup server - and it backs up our exchange server over the network.

It is rather strange now as the client machines are pointed in the right direction from the DNS server.
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Author Comment

by:gwalker_ne8
ID: 12004959
Using NSLOOKUP on the DNS server I get:

nslookup exchange
Server:  dns-server.***.***.co.uk
Address:  DNS address

Name:    exchange.***.***.co.uk
Address:  Internal address

However when I ping exchange:

Pinging exchange.***.***.co.uk [External address] with 32 bytes of data:
Reply from External address: bytes=32 time<1ms TTL128

And when I ping -a "exchange internal address" it will resolve the address to the exchange servername.

When I flushed the DNS I could ping the server by name for a while, then it went back to external.

Thanks for the help Adam.
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Expert Comment

by:adamdrayer
ID: 12004974
I'm running out the door now, but I'll be back on at about 9:00am when i get to work
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Accepted Solution

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adamdrayer earned 500 total points
ID: 12011801
make sure your internal DNS server has both a forward a reverse record for your exchange server.  Make sure it's only DNS server is "127.0.0.1".  Then clear the cache and try again.
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Author Comment

by:gwalker_ne8
ID: 12014034
Right, in our DNS server under our zone in forward we have say:

exchange          A             10.0.0.105

In our zone reverse we have it under 0.0.10.in-addr arpa:

105                  PTR         exchange.***.***.co.uk

However I have just discovered that something is up with the domain DNS, if I ping the domain name from my machine it replies from another server on our domain, not the primary AD, moreover when I ping it from the DNS/Primary AD server I get an address i do not recognise an 195.82.***.*** address.

I have cleared the cache, however I don't even get the few moments of the correct address this time.
I think I have further screwed things up.

Would you like me to get all of the options selected in the server and both forward and reverse DNS properties?
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Author Comment

by:gwalker_ne8
ID: 12014322
When I do a nslookup from the server and client machines I get:

Server: DNS server.***.***.co.uk
Address: DNS server address

DNS request timed out.
       timeout was 2 seconds.
*** Request to DNS server.***.***.co.uk timed-out
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Author Comment

by:gwalker_ne8
ID: 12014346
sorry nslookup for the domain. /\
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Author Comment

by:gwalker_ne8
ID: 12014431
Wait a sec...  Our server support company have added the ISPs address to the server as a second DNS?!!??!  :#  OMG, removed that and bang, I think thats it, lets see... :)
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