Resolver timeouts, EDNS and networking

Danny Mayer mayer at
Sun Sep 30 03:18:15 UTC 2007

Christian Robottom Reis wrote:
> On Thu, Sep 27, 2007 at 04:20:09PM -0700, Chris Buxton wrote:
>> If it were me, I would start by disabling EDNS0. This is often the  
>> cause of problems such as this. You can try setting the buffer size  
>> down to 512 bytes, but if that doesn't solve it, turn EDNS off entirely.
>> If that solves it, then probably the forwarders are the problem. Ask  
>> your ISP about this; they may be using some kind of security software  
>> that is not able to handle EDNS0.
> Can I reliably detect whether my forwarders handle EDNS0 or not? I have
> tried manually querying them using host and dig (with +bufsize) and they
> seem to reply without a problem, but I'm not sure if that is a valid
> test.

Don't use forwarders unless you have specific circumstances requiring
it. They are rarely necessary and cause more problems than you gain from
using them. There's no advantage to using them.

>> There will always be some timeouts. That's just the nature of the  
>> Internet today. But these should not result from a large percentage  
>> of your server's resolving attempts.
> Thanks for reassuring me. I'm trying hard to get better service to my
> users -- and intermittent or random failures are particularly
> bothersome.

Which is another reason not to use forwarders.


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