Content Delivery Networks

Rodney Joffe rjoffe at
Fri Aug 10 14:52:02 UTC 2007

On Aug 9, 2007, at 10:55 PM, Paul Reubens wrote:

> How do you engineer around enterprise and ISP recursors that don't  
> honor TTL, instead caching DNS records for a week or more?

In my "little" bit of research and experience over the last 10 years  
in this field, I have often pursued this "urban myth". It remains  
largely just that.

The most common  supposed violator of this was AOL. I found myself in  
a position at one stage to get to the "root" of this, and was rather  
impressed to find that it was indeed a myth.

We've just finished a small research project where we looked at  
approximately 16 million recursive servers. The only ones violating  
this were some CPE devices that ran local recursive services, and  
they were generally along the lines of returning the appropriate TTL  
the first time they were queried, and if the TTL was zero, they  
returned a higher TTL (10000 seconds) to subsequent queries for a  
short period (5 minutes). It may have been a code bug, or a designed  
behavior given that these were CPE devices.

Do you have any real examples of significant recursive servers doing  

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