SERVFAIL?!

[Michael Voight]

Additionally, if you do not have your reverse domains set up correctly,
DNS queries are going to go to the internet to resolve PTR records
whenever someone connects to a server.

Michael

Jim Reid wrote:
> 
> >>>>> "David" == David Brueckmann <brueckmann at mycontrol.de> writes:
> 
>     David> I have a customer with a mailserver (sendmail) connected
>     David> via dialup running.
> 
>     David> I need the forwarders because these are the only
>     David> nameservers this machine can reach.
> 
> Hmm. Forwarding isn't usually a good idea with a dial-up link, but if
> that's all they've got......
> 
>     David> The problem is: Sometimes (every 4-5 days) there are many
>     David> entries like
> 
>     David> named[130]: sysquery: findns error (SERVFAIL) on
>     David> mailin01.btx.dtag.de?
> 
>     David> in my syslog and the machine dials up about 40 times per
>     David> day.
> 
>     David> What is the problem?
> 
> The "findns error" means that your name server was unable to find any
> name servers for the btx.dtag.de or maybe the dtag.de domains. [I'm
> assuming that the .de name servers haven't vanished from the net.] Use
> host or dig or nslookup - I can't be bothered - to find the NS records
> for these domains and then resolve them to IP addresses. Then query
> those IP addresses for stuff in the btx.dtag.de or dtag.de domains.
> [Asking them for the MX and/or A records for mailin01.btx.dtag.de
> would seem to be worthwhile.] This should identify where the broken
> delegation occurred. These NS records either point at unresolvable
> names or else they resolve to A records which don't run name servers
> for one of the two domains.
> 
> Since your name server can't find name servers for these domains,
> lookups for mailin01.btx.dtag.de fail. This might cause sendmail to
> queue the mail and retry the delivery later. So the next time the
> mail queue is run, sendmail looks up mailin01.btx.dtag.de, gets a
> SERVFAIL error, and queues it again. That could explain 40 or so error
> messages in the log. Or perhaps something at the customer's site is
> trying to send 40 or so mail messages to mailin01.btx.dtag.de every 4
> or 5 days....
> 
> To fix this, you need to find the broken delegation and get the
> hostmaster for that domain to fix it so that the world can lookup
> mailin01.btx.dtag.de successfully. It might also be possible to change
> sendmail so that SERVFAIL errors from the DNS cause mail to be
> bounced. There's bound to be an option somewhere in sendmail.cf to
> switch this off or on. This might reduce the number of messages in the
> logs.