Command/scripts to check the Reverse DNS Lookup time

Question

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.

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.

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