DNS question

Posted on 2012-09-04
Medium Priority
Last Modified: 2012-09-10

I have the following question.
When I do nslookup in our domain I get below results:

Nslookup to mac-023 gives
Nslookup to gives lt-016
Nslookup to lt-016 gives and
- Nslookup to gives label-logistic
- Nslookup to gives lt-038

As you can see for example from mac-023 result = but in reveres it doesn't give mac-023.

Our external helpdesk say that this is a none issue, and that this doesn't give any problems.

Are they correct, or are there any known issues when this happens.
Question by:thecookiecompany
LVL 19

Expert Comment

by:Delphineous Silverwing
ID: 38363766
Did you perform each lookup from the same computer against the same DNS server?  If so, this may be indicative that the Forward Lookup Zone and Reverse Lookup Zone do not match - often caused by system latency or corruption in the database.  BUT don't be fooled by your own workstation caching these results.

Try the same queries from another computer and see if you get the same exact results.  What happens to these results if you reboot and try again?

Most company networks use DHCP (dynamic addressing) and machines may change addresses.  If DNS scavenging is not functioning, then stale entries can exist causing this symptom too.

Author Comment

ID: 38363873
@Delphineous: Just tried it on a second computer and the results are the same as from my own workstation.

Our company network is using DHCP for the most system, only servers have fixed IP adress.

Are there any problems (like slow networking) known?

The ressaon I ask this is: When I monitor our SQL server, I see computer names for example mac-023 which is not using this SQL server. So doing nslookup tells me that i can also be lt-016. That one can be using the SQL server.
LVL 29

Expert Comment

by:Jan Springer
ID: 38363901
The forward and inverse zones should match (excluding virtual hosts -- of which there will only be a forward entry).

Have whoever takes care of your DNS correct this.

Accepted Solution

amitnepal earned 2000 total points
ID: 38364041
To answer your original question, the reverse look up mismatch should not cause any slow down or other adverse effects in your network. Usually reverse look up is not even cared in general environments . Reverse look up is greatly used to verify the identity or the origination in Mail servers to reduce spam. For  example for a mail server it is required to match the smtp banner with the reverse look up name of the server. In your case it should not be a problem.

Thank you

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