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DNS question ..reverselookups ?

DNS question ..reverselookups ?

Does a HP-UX host ( previously configured as a DNS client) continue to use DNS services , especially reverselookups , even if the /etc/nsswitch.conf file has been modified not to use DNS anymore and use host files only ?
I had a host configured as a dns client , but today I had some connectivity issues (gwan problems, effecting the name servers )which was causing timeouts to happen on the Oracle db on this particular host. I then went in and hashed out the entried in the /etc/resolv.conf and modified the /etc/nsswitch.conf to not use dns anymore and just use hosts, but connectivity/timeout problem still persisted. If I did a nslookup ,it showed that it was only using the hosts file. The slow connectivityproblem was solved only once the gwan issues were resolved.
Also I was told by the Wintel guys ( the name servers I am suing are windows boxes )that according to the logs on the nameservers they could see that my unix host was still trying to do reverselookups , even thought I did not have dns in my nsswitch.conf ? I am a bit surprised .
Regards,
Roy
4 REPLIES
Vitaly Karasik_1
Honored Contributor

Re: DNS question ..reverselookups ?

If you remove the pointer to DNS server from resolv.conf and leave "hosts" only into nsswitch.conf, your machine shouldn't use DNS. May be you have some application which use its own resolver library?
Bill Thorsteinson
Honored Contributor

Re: DNS question ..reverselookups ?

You don't need to modify resolv.conf to
turn of DNS lookups, just nssswitch.

If you are runing nscd or the like you may
need to restart them after modifying
/etc/nsswitch. Long running applications
which use the resolver library will likely
also miss the changes to nsswitch.conf.
They should be restarted.

Re: DNS question ..reverselookups ?

Thanks for your input guys.
Looks like the issue is not unix related anymore .
regards,
Roy

Re: DNS question ..reverselookups ?

Does not seem to be a problem at the Unix end anymore, looks more like a windows application issue