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

[Joe Fernandez <jfernand@kardinia.com>]

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