Re: Name lookup question

[Stephen Gardner <stephen-rhel uk org>]

On Thu, 12 May 2005, Collins, Kevin  [MindWorks] wrote:

> Hi,
>
> 	this is something that has puzzled me for a while, and I like to
> get it solved if possible:
>
> In our environment, we rely heavily in NIS. Our name resolution is
> configured in nsswitch.conf to use NIS, then hosts file, then DNS
> (host.conf is also configured this way). We have many short host name
> aliases in NIS that we use for convenience that are NOT in DNS or local
> hosts file. From the OS perspective, this all works well.
>
> If I attempt a ping to one of those aliases, all works well - the name
> is resolved to IP and the ping succeeds. However, if I attempt to use
> the nslookup or host command to lookup the alias manually, it fails with
> a SERVFAIL error.
>
> Shouldn't these commands be using the name service switch just like the
> rest of the OS, or am I spoiled because HP-UX works the "right" way?

Kevin,
   I guess the main difference is in the tighter coupling of the HP-UX 
resolving code. nslookup (and host) is part of ISC Bind and generates 
queries directly to DNS servers (with the aid of /etc/resolv.conf). 
Applications are usually linked to the libresolv which is part of glibc. 
When applications generate queries (such as gethostbyname) which come via 
libresolv, glibc can make use of /etc/host.conf and /etc/nsswitch.conf to 
determine the resolvers to use and the order to query them. It sounds as 
though under HP-UX the nslookup code is built to use the systems resolver 
library when doing lookups but in RHEL the libc resolver and the nslookup 
code are written by different groups of people with different objectives. 
nslookup from ISC Bind (in RHEL) is written to do DNS lookups, nslookup 
in HP-UX is a front-end to the resolver library.

Regards,
   Stephen