FW: DNS TTL adherence

Thurman, Steven steven.thurman at wamu.net
Wed Mar 15 17:34:21 UTC 2006

On Wed, 15 Mar 2006, Simon Waters wrote:
> > This behavior is unfortunately not unique.
> Alas what others peoples servers do, shouldn't be an issue for you.
> problem is they can be coerced into a DoS attack, not that the data is

>actually, dos-attack-aside, the interesting thing is that lots of
>(original poster perhaps included) believe that TTL's are adhered to
>except in some marginal cases. I think Rodney's point is that they are
>adhered to anywhere near as much as we would all like to believe :(

>So, if you, or the original poster, is going to move
>around ip-wise keep in mind that your ${important_thing} may have to
>answer to more than 1 ip address for a period much longer than your
>TTL :(

Thanks all for the responses. I do understand we may need to support the
old IP addresses for sometime. I was hoping someone had performed a
study out there to determine what a ratio maybe for us supporting an old
IP address (I know our traffic profile will be unique for us thus it
would only give us a general idea). 

For example if we change ip addresses will we need to plan on 20%
traffic at old site on day1, 10% day2, 5%, day3, and so on...? There are
also issues related to proxy servers and browser caching that are
independent of DNS we will need to quantify to understand full risk. The
more data we have will drive some of our decisions.

Thanks again,


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