nslookup flaws

[Brad Knowles]

At 12:10 PM +1000 7/6/01, Nathan Jones wrote:

>  I believe there are problems with nslookup, but I'm having trouble
>  finding out specifically what they are.
>
>  Can someone here point me in the right direction?

	For starters:

		1.  nslookup requires that reverse DNS be configured for
			the nameservers listed in /etc/resolv.conf.  If you've
			got a DNS problem, that's just as likely to affect your
			ability to serve reverse DNS as it is anything else,
			so when you most need nslookup to work, is when it is
			mostly likely to fail.

		2.  Even with all debugging options turned on, nslookup
			doesn't show you everything that's going on with the
			query, or all the data returned.

		3.  Most vendor-supplied versions of nslookup have been
			hacked to by-pass the DNS and to include resolution
			involving things like /etc/hosts, NIS, etc....  This
			just confuses the issues.  Sometimes there are times
			when you want to debug these non-DNS name services,
			but nslookup should not be doing this without your
			requesting it to do so.

		4.  Even when querying just the DNS, nslookup by-passes
			the standard resolver routines, so when nslookup does
			a query, that's not following the same code path as
			when a program does a query, and therefore using
			nslookup may not tell you anything about where the
			problem may be -- nslookup may work fine when the
			program doesn't, or nslookup may fail when the
			program works fine.

	I'm sure others on the list can add to these items.

-- 
Brad Knowles, <brad.knowles at skynet.be>

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