topic Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf in Operating System - HP-UX

DNS lookup's going to old nameserver after changing /etc/resolv.conf

David Manson — Sun, 14 Aug 2005 23:25:53 GMT

Hi all,
We have recently replaced a couple of old DNS nameservers in our network, but after having updated the /etc/resolv.conf file on this particular server, with the details of the new DNS nameservers, we still find that DNS queries are being sent to the old nameservers.
My problem is that I am unsure of the effect on this server when the old nameservers are switched off.
In an attempt to resolve this I have tried a SIGHUP of inetd, but still have the same problem.
I would prefer to avoid a complete server restart if possible, so would be interested in any suggestions on how to resolve this problem.

Thanks.

Regards,
Dave

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Joseph Loo — Mon, 15 Aug 2005 00:42:56 GMT

hi,

since u have restarted inetd but the same problem persists.

have u confirm that amendment made to /etc/resolv.conf is correct or would u like to post it here?

regards.

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Yogeeraj_1 — Mon, 15 Aug 2005 00:51:28 GMT

hi,

on windows clients, you can try to run: ipconfig /flushdns

on the hp-ux server, i don't know if something similar exists!

can you try to run nslookup and see what is really happening?

regards
yogeeraj

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Thayanidhi — Mon, 15 Aug 2005 01:02:45 GMT

Hi,
Post the content of /etc/resolv.conf and /etc/nsswitch.conf
If names are used /etc/hosts needed.
How did you conclude the server is still looking at the old DNS server?

Regds
TT

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Bill Hassell — Mon, 15 Aug 2005 09:31:21 GMT

When testing DNS servers, use the explicit server option in nslookup, something like this:

nslookup www.hp.com 12.34.56.78

where 12.34.56.78 is the specific nameserver to query. Then use nslookup without the 12.34.56.78 server and it should report the same results. However, the actual behavior of resolving hostnames depends on /etc/nsswitch.conf and often needs to be changed.

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Matti_Kurkela — Mon, 15 Aug 2005 09:34:01 GMT

Most programs that use DNS will do so using a name resolver functions in a library provided by the OS.

When the application starts, it will load and initialize the library with the resolver functions if it needs DNS. Reading /etc/nsswitch.conf and /etc/resolv.conf is one part of the initialization code of that library.

This means most programs will read /etc/resolv.conf only at the point when they're starting up. To activate the new settings, you must stop and restart the application.

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

David Manson — Mon, 15 Aug 2005 16:57:26 GMT

Thanks for all the replies.

In answer to your questions ...

The amendment made to /etc/resolv.conf is correct (same used across many other servers).

nslookup is resolving correctly ... it appears to be a running process that is still querying the old nameserver.

Our network team records all IP's querying this 'old' nameserver, which is how I can identify this particular server.

I will try Matti's suggestion and stop and restart the applications on this server.

Thanks again.

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Mike Duffy_1 — Thu, 18 Aug 2005 09:48:51 GMT

Dave,

did you check that none of the apps was caching DNS entries? Also could it be that your box is running as a name caching server.

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Rita C Workman — Thu, 18 Aug 2005 10:11:26 GMT

hmmm....

..well fixing your /etc/resolv.conf is something you should have done.

I'm no DNS expert...but on ours we have to fix the master DNS configuration file when we remove or change DNS servers - and then we have to run the command to rebuild DNS from the hostfile (with the new host info now added) ??

Just a thought,
Rita

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

Tim Nelson — Thu, 18 Aug 2005 13:10:12 GMT

Dave,

Just a dumb question. Is this host a named server ? or client ?

All changes I have ever made to a client in the resolv.conf file are immediate (hence the name Dynamic Named Service).

nslookup
> server localhost
> set swtrace
> set debug
> host_to_look_up

The output from the above may help troubleshoot.

Re: DNS lookup's going to old nameserver after changing /etc/resolv.conf

David Manson — Thu, 18 Aug 2005 16:45:51 GMT

Thankyou all for your replies and suggestions.

I have resolved this problem by restarting the server. It is now issuing queries to the new nameservers.

regards,
Dave