Debugging recursive bind

[Kevin Darcy]

Marco Michelino wrote:
> Hi all,
> I have a recursive dns server that sometimes returns errors on queries
> even if the requested domain exists:
>
>
> # dig @myserver agriturismolacapraccia.it mx
>
> ; <<>> DiG 9.3.4-P1.1 <<>> @myserver agriturismolacapraccia.it mx
> ; (1 server found)
> ;; global options:  printcmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 12554
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0
>
> ;; QUESTION SECTION:
> ;agriturismolacapraccia.it.     IN      MX
>
> ;; Query time: 34 msec
> ;; SERVER: XX.XX.XX.XX#53(XX.XX.XX.XX)
> ;; WHEN: Fri Nov 21 10:59:14 2008
> ;; MSG SIZE  rcvd: 43
>
>
> My log file shows no error... how can I debug the query to understand
> what's going wrong?
>   
SERVFAIL is a catch-all error and many different things can cause it.

In real-time, you could try the +trace option to dig.

Offhand, the only thing that strikes me about this is that both 
nameservers for
agriturismolacapraccia.it appear to be on the same network segment 
(85.18.235.2 and 85.18.235.4). This would make their nameservice rather 
fragile. It's likely they have a Single Point of Failure which could 
cause their whole domain to be temporarily unavailable.

- Kevin