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I am working on a project in which one master communicates with numbers of slaves. For that it has to make connection with hosts in network. But sometimes it hangs.

I think that the reason behind is extra time consumption during Reverse DNS Lookup. So please tell me any command or script which checks or makes the list for the Reverse DNS Lookup time.

EDIT no. 1

Tell also that where can I add that command in rsh source code so that I got a list of time consumed by every request, whenever it connects to other hosts.

So that I can find the reason behind the hanging of server.

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Yes it does a reverse dns lookup. –  devnull Feb 22 '13 at 13:42
    
Can you tell where can I add this command in rsh source code, so that I can check, Reverse DNS lookup time, or, if I am wrong then correct me. Please. –  devnull Feb 24 '13 at 7:07
    
question edited... –  devnull Feb 25 '13 at 4:18
    
Actually my task is the same that I Edited. But my question is the approach that I thought. –  devnull Feb 25 '13 at 12:42

1 Answer 1

If you have doubts in Slow response in reverse query then you can try below method to rectify the same.

  • Method 1

if possible then disable reverse lookup in your application and see the difference

  • Method 2

You can use Name Service Cache Daemon (nscd) which also caches PTR but there is some Securities issue as :

The Name Service Cache Daemon (nscd) has a default behavior that
does not allow applications to validate DNS "PTR" records against
"A" records.

In particular, nscd caches a request for a "PTR" record, and when a request comes later for the "A" record, nscd simply divulges the
information from the cached "PTR" record, instead of querying the
authoritative DNS for the "A" record.

Reference Link

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These are the lines from given links Important! If you are running a service that relies on forward/reverse lookup checks, don't do this!. –  devnull Feb 26 '13 at 5:02
    
But firstly I want to make a table of time consumed in Reverse DNS Lookup. Tell me how can I do this first. I want to analyse the delay first. Solve my problem. If this is the reason then I can apply your methods. –  devnull Feb 26 '13 at 5:09

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