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104 posts

Master Geek

# 67701 7-Sep-2010 11:18
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Hi all
A couple of my customers, all Telecom Broadband business users, have suddenly been unable to perform DNS lookups using servers outside Telecom.  I.e. the root hints on their DNS servers have stopped working.

A manual nslookup fails (timeout) but I can successfully use Telecom's DNS servers.
My best guess is that Telecom are blocking 53/udp to external domains.
I have noticed that it is intermittent, so not sure if its an international congestion thing, and perhaps the lookups are simply timing out?  Maybe something to do with the Canterbury earthquake?

I've adjusted the DNS servers to use forwarders to Telecom instead of Root Hints, and all is working fine, but WTF is going on here?  I can find no mention of anything or anyone else having problems, on Telecom's website nor via Google.

Has anyone else had issues, or know whether changes have indeed been made?


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677 posts

Ultimate Geek


  # 377468 7-Sep-2010 11:52
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Hi drjay,

As far as i am aware we do not restrict 53 tcp/udp at all, we don't redirect it either.
I would suggest that using our name servers as forward-first on bind is a good practice give the caching, CDN and google caches in the network.



meat popsicle

234 posts

Master Geek

  # 377470 7-Sep-2010 11:54
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I had the same problem this morning too (until about 30mins ago), but it has resolved itself without any intervention on my part. I know of others that have had data connection problems this morning too, but no idea if it was specifically DNS or not. I am in Taranaki.

PS. My home broadband was fine. This was only an issue on mobile broadband (XT). 


104 posts

Master Geek

  # 377478 7-Sep-2010 12:15
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Thanks Paul, good to have word from the horses mouth (so to speak).
I'd guess that it's congestion then, which I'll check by using the "set timeout=" option in nslookup. This would fit with the other reports of slow traffic.

I must say I prefer to use root hints, much like I prefer to deliver direct via smtp, but with DSL being essentially a dial-up technology we're forced to use mail relay via ISP, so DNS forwarders via ISP isn't a big stretch!

Not sure if it means anything, but setting the forwarder to the DSL router results in even worse responses - I am guessing that the routers (DLink DSL-504 and similar consumer models) just don't have the horsepower or RAM to server as commercial DNS resolvers/caches :-)

677 posts

Ultimate Geek


  # 377484 7-Sep-2010 12:24
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No problem.
That would certainly be true, I have seen many routes that cant handle large numbers of DNS requests and perform reasonably badly when you try to force them.

The resolvers we have certainly aren't DSL routers:P

I don't know about congestion sorry, not something i have visibility of.

Using your own DNS is fine if you know about the gotchas and those gotchas wont have any impact on you.



meat popsicle

104 posts

Master Geek

  # 377502 7-Sep-2010 13:18
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Interesting recent post:
Gotta wonder if there is a general congestion issue or perhaps even an upstream technical problem - this site is frustratingly slow for me today and its the ads that are the problem, not the local content.

Nslookups to the root hints and subsequent referral servers all respond OK now (instantly) so not sure if the issue has vanished, or if it is simply one of those intermittent times when the lookups would have worked under the original setup.

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