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Re: [OT] Bonehead DNS question

From: jb000002@xxxxxxxxxxxx (JB)
Date: 19 Oct 2006 04:06:55 GMT
Cache-post-path: dr-f.mr-happy.com!unknown@crow.mr-happy.com

This got a bit long.  My apologies to those not interested.

In <4536e79f$0$788$415eb37d@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
walt  <wa1ter@xxxxxxxxxxxxx> shouted to everyone in earshot,
>Using a packet sniffer, I can see that my server fetches the
>names of at least four backup servers at BBC -- but then my
>server insists on resolving those names by using the primary
>server which is *down*, and so the whole effort fails.

What's your nameserver software and version?  Care to post (or e-mail
to me) your named.conf if it's BIND?  (Just the global settings and
such probably don't need any zones you have configured, unless one of
them is bbc.co.uk or bbc.net.uk. =) )  Is your nameserver reachable
from the Internet?  If so, do I have your permission to run some
queries against it?  You can e-mail me its IP address if you'd rather
not post it.

I'm seeing some sort of weird stuff, too.  I used to consider myself
quite knowledgable in DNS matters, but the dwindling of my youthful
conceit combined with my decreasing effort to keep up with more than
basic DNS practises has me wondering if what I'm seeing is truly odd
or sort of normal.  So I'll post it here in case anyone more clueful
than me can see what's going on.

$ host www.bbc.co.uk
www.bbc.co.uk is an alias for www.bbc.net.uk.
www.bbc.net.uk has address
www.bbc.co.uk is an alias for www.bbc.net.uk.
Host www.bbc.co.uk not found: 2(SERVFAIL)

Output is identical every time I run that command.  I'm guessing
'host' is sending out four queries and hitting the down nameserver for
one of them.

$ host www.bbc.net.uk
www.bbc.net.uk has address
Host www.bbc.net.uk not found: 2(SERVFAIL)

That seems a little stranger, because I clearly *do* get an answer.
Using 'dig', I get an answer and no error.  This is 'host' from BIND
9.3.2-p1, built as part of recent FreeBSD 6-STABLE (6.2-PRERELEASE).
named is running under OpenBSD 3.4, BIND 9.2.2.  Same general
behaviour from BIND 9.3.1 host/named under FreeBSD 5.4-RELEASE.

$ dig in ns bbc.co.uk
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;bbc.net.uk.                    IN      NS

If I try that a few times, I eventually get an answer, which is then
cached by my nameserver.

$ dig in ns bbc.net.uk
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 0

;bbc.net.uk.                    IN      NS

Haven't gotten an answer for this one yet.  I assume both of these are
also related to the down nameserver.

$ dig in a www.bbc.net.uk
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 2, ADDITIONAL: 2

;www.bbc.net.uk.                        IN      A

www.bbc.net.uk.         296     IN      A

bbc.net.uk.             172796  IN      NS      ns0.thdo.bbc.co.uk.
bbc.net.uk.             172796  IN      NS      ns0.thny.bbc.co.uk.

ns0.thdo.bbc.co.uk.     84601   IN      A
ns0.thny.bbc.co.uk.     84601   IN      A

. ..Despite the fact that I can't dig my local nameserver for the
bbc.net.uk nameservers, I still get the list as glue.  And that
situation is reproducible with any combination of nameserver and unix
tools on machines I operate.

Of course, digging at the nameservers in the NS records for both those
domains results in an immediate answer unless it's the one down
nameserver, ns1.bbc.co.uk.  bbc.net.uk's two nameservers are also two
of the operational nameservers for bbc.co.uk.

Anyway, I have no clear idea of your problem, but if you're not
running BIND named, perhaps what you're running has a quirk or bug of
some sort.  I would think that most nameservers' caching behaviour is
sane out-of-the-box, but I have little experience outside of BIND.  I
can load up the web site in question as well, even though ns1 is
apparently down.

I hope this at least sheds some light on the problem for someone here
who knows more about this sort of thing.


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