Slashdot: Providers Ignoring DNS TTL?

Tue Apr 19 21:30:40 UTC 2005

Fergie (Paul Ferguson) wrote:

> 
> Interesting thread on /. --
> 
> http://ask.slashdot.org/article.pl?sid=05/04/18/198259&tid=95&tid=128&tid=4

FWIW, I did some 'dig'ing on my Comcast home service. The DHCP is handing
out 204.127.198.4 and 63.240.76.4 for DNS at the moment.

I ran a query for a name in a zone I control that has a five minute TTL
on 204.127.198.4. The first query came up with 5 minutes. I quickly made
a change to the zone. hirty seconds after the initial query, I try again...
err... and come up with the change. Hmm... Not caching at all? Another
30 seconds and I get the change, with 5m TTL. Thirty seconds later, I
get the original response with appropriately decremented TTL. Another
thirty seconds, I get the change, with 4m TTL.

My findings: Comcast is now using some kind of load balancing that messes
with this kind of testing. 204.127.198.4 is not a single resolver. However,
as far as I could tell, they were obeying the TTL. After 5 minutes, all
of the responses were coming back with the change. The TTL values in the
responses were decrementing as expected.
-- 
Crist J. Clark                               crist.clark at globalstar.com
Globalstar Communications                                (408) 933-4387