Re: [nv-l] Re: Help with name resolution on Linux

[Leslie Clark <lclark@us.ibm.com>]

Yes, please! I'd appreciate it. 

Cordially,

Leslie A. Clark
IBM Global Services - Systems Mgmt & Networking
(248) 552-4968 Voicemail, Fax, Pager

Joe Fernandez <jfernand@kardinia.com>
Sent by: owner-nv-l@lists.us.ibm.com

12/22/2004 08:56 PM

Please respond to
nv-l

To	nv-l@lists.us.ibm.com
cc
Subject	Re: [nv-l] Re: Help with name resolution on Linux

At 01:19 PM 21-12-04 -0500, you wrote:
Has anyone encountered this? I'm trying to override DNS
with /etc/hosts. It appears that you do this in /etc/nsswitch.conf and
/etc/host.conf on Linux, similar to Solaris. And the host command behaves
differently than it does on AIX - it always checks only dns, like nslookup.
The same with the 'dig' command. So it is tricky to verify just what is
going on. It appears to me that it works for forward resolution, but not
for backward resolution. 

That is,  gethostbyname  respects the order that you set in nsswitch.conf
     hosts:  files dns 
and in /etc/host.conf 
     order hosts, bind 
     multi on 
but gethostbyaddr does not. 

Suggestions welcome. 
Cordially,
Leslie A. Clark
IBM Global Services - Systems Mgmt & Networking
(248) 552-4968 Voicemail, Fax, Pager 

Leslie,

I believe "dig" is meant to only look up the DNS.

On the other hand, both gethostbyname and gethostbyaddr will do a search
in the order you specify in the nsswitch.conf and host.conf files as you
 list above.

I ran a check on one of our Red Hat systems.

1. The default settings of the conf files were as you have them above,
without the "multi on"
2. I executed a gethostbyname on www.ibm.com,
got a list of IP addresses, picked one and issued a gethostbyaddr and got
back www.ibm.com
3. I made an entry in the hosts file defining www.ibm.com
as 10.1.1.1
4.  I executed a gethostbyname on www.ibm.com,
got 10.1.1.1, executed a gethostbyaddr on 10.1.1.1 and got back www.ibm.com
5. I reversed the order in the conf files, repeated the previous step and
got the results of step 2 rather than step 4.

This suggests to me that both gethostbyname and gethostbyaddr  take
their order from the conf files....at least on this system.

I can send you the command line program I used to test it, if it is of
use to you.


Joe Fernandez
Kardinia Software
jfernand@kardinia.com
http://www.kardinia.com