On Wed, 7 Mar 2001, Paul Lussier wrote:
> In debugging DNS issues, I'd like to know what servers my DNS lookups are
> hitting to make sure things are set up correctly.
Briefly: No. The way DNS works does not lend itself to such things.
At length:
It depends on where the recursion occurs. Remember, the average user
program does not perform DNS recursion. Rather, the server the user program
queries will do it. If you are deep in a DNS cache hierarchy, recursion may
in fact occur at multiple levels at different times. In many -- if not most
-- cases, the client making the initial DNS query is only going to see the end
result.
> For instance, I'd like to test that when my main DNS server is down, that
> my secondary is taking over. I'd like to have the warm fuzzy of
> traceroute-like output telling me that the query went to a root server,
> the the .com server, then finally dns2.foo.com.
For what client? A client in your network might normally query an
authoritative name server for "foo.com" anyway. Some random system on the net
is going to query some random name server, which is going to actually do the
recursion. Or the server might have cached entries for the entire period that
"dns1.foo.com" is unavailable, so you end up testing nothing.
Your best bet is to use dig(1), and manually follow the DNS resolution
algorithm. Set the +norecurse option. Use a query type of ANY. Query FQDNs
ending in a period:
foo.com.
^--- note period
Start by querying with "@a.root-servers.net". Pick one of the authoritative
servers it responds with, and query that one. Repeat until you get the list
of name servers authoritative for "foo.com". Then query *each* and *all* of
those name servers, and make sure they all report mutually consistent results.
--
Ben Scott <[EMAIL PROTECTED]>
Net Technologies, Inc. <http://www.ntisys.com>
Voice: (800)905-3049 x18 Fax: (978)499-7839
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