"no data known" vrs "host not found"

Barry Margolin barmar at genuity.net
Mon Mar 25 22:09:54 UTC 2002


In article <a7o6oo$m35 at pub3.rc.vix.com>, admjcd  <admjcd at VOLPE.DOT.GOV> wrote:
>Yes, but it fails when I do an nslookup on my DNS server when it fails
>with the mail.  So if we are getting the NDR I do an nslookup with the
>type set to MX and get the "no data found" "authoritative answer"
>response.  But when I do the same lookup at other dns servers on the
>internet and the dns servers for the domain in question I get a correct
>answer back while mine is failing.

It sounds like negative caching.  The mailer's query caused your server to
cache the fact that the MX record doesn't exist, and your nslookup is then
seeing this.

Since the other servers don't have the negative cache entry (because none
of their client machines had recently performed an ANY query for the
domain), when you query them they will forward the query to the
authoritative server, and return the MX record properly.

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
*** DON'T SEND TECHNICAL QUESTIONS DIRECTLY TO ME, post them to newsgroups.
Please DON'T copy followups to me -- I'll assume it wasn't posted to the group.


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