TTL from SOA is smaller than TTL from local DNS!

Edward Lewis Ed.Lewis at neustar.biz
Thu Apr 12 13:49:44 UTC 2007


At 14:55 +0200 4/12/07, Stephane Bortzmeyer wrote:
>On Thu, Apr 12, 2007 at 08:46:38PM +0800,
>  Vishwas <ivishwas at gmail.com> wrote
>  a message of 33 lines which said:
>
>>  Look at the fourth row, the difference between the TTLs is negative!
>>  Under what circumstances the difference between the TTLs should be
>>  negative?
>
>For instance, if youtube.com just changed to smaller TTLs.

More likely it is this:

$ dig @e.gtld-servers.net. dns2.sjl.youtube.com. +noall +answer
dns2.sjl.youtube.com.   172800  IN      A       208.65.152.137

$ dig @dns2.sjl.youtube.com. dns2.sjl.youtube.com. +noall +answer
dns2.sjl.youtube.com.   3600    IN      A       208.65.152.137

The recursive server has only seen the "less trustworthy [RFC 2181]" 
address record for this server.  Had the latter record been seen, the 
TTL would be lower.  The 172800 value used throughout the .com zone.

Try this - do a "dig dns2.sjl.youtube.com a" and look at the TTL, you 
should see it drop to 3600 and then decrement 1/second.  What that 
does is "seed" the cache with the authoritative address record.
-- 
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Edward Lewis                                                +1-571-434-5468
NeuStar

Sarcasm doesn't scale.



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