North American Network Operators Group
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Re: DNS TTL adherence

  • From: Rodney Joffe
  • Date: Wed Mar 15 09:18:43 2006 
On Mar 15, 2006, at 1:56 AM, Simon Waters wrote:

In answer to the original question, I'm not aware of any DNS servers that
don't expire data at the end of the TTL period correctly. Failing to expire
such data would be a good way of breaking things, and people would just not
use such broken software.
Let me help you become aware, then...

I'm not sure why the OP thinks someone would research such a bug in detail, my
experience is they would just fix it.
Some people don't believe it is a bug, and therefor don't see that anything needs "fixing".

Feel free to, for example, send 2 consecutive queries for a record that has a short (<10,000 second TTL) to 212.23.11.206. This is one of the over 100,000 random open recursive servers that have been party to some of the recursive DNS server amplification DDoS attacks over the last few weeks... and this behavior exists in a number of them.

If you can't think of a record to query for that has a short enough TTL, I've created a wildcard entry of:

*.example.centergate.com

so that you can test this repeatedly without having to wait for the overridden TTL to expire. Just use a different random wildcard record each time (remembering to send 2 consecutive identical queries to see the misbehavior).

$ dig @212.23.11.206 jhgfd.example.centergate.com a


This behavior is unfortunately not unique.

/rlj