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# What is the maximum TTL Value i can set for DNS Entries?

Posted on 2007-04-07
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What is the maximum TTL Value i can set for DNS Entries? Such as A, MX, CNAME ?

I'm more interested in an article describe it in more detail than just a number but either one would work.

thanks,
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Question by:MichaelPro
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Expert Comment

ID: 18870325
Hello MichaelPro,

My O'Reily book on DNS & Bind appears to imply that the maximum TTL is 99,999,999 seconds. Approximately 3.1 years. Either that or 3,600,000 seconds, approx. 41 days. To know for definite, I would suggest reading the RFC's.

Regards,

InteraX
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Accepted Solution

InteraX earned 400 total points
ID: 18870331
MichaelPro,

Just found this.
8. Time to Live (TTL)

The definition of values appropriate to the TTL field in STD 13 is
not as clear as it could be, with respect to how many significant
bits exist, and whether the value is signed or unsigned.  It is
hereby specified that a TTL value is an unsigned number, with a
minimum value of 0, and a maximum value of 2147483647.  That is, a
maximum of 2^31 - 1.  When transmitted, this value shall be encoded
in the less significant 31 bits of the 32 bit TTL field, with the
http://www.rfc-editor.org/rfc/rfc2181.txt
specified in 1997.

InteraX
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Expert Comment

ID: 18870333
MichaelPro,

That appears to imply 68 years!!! ;-)

InteraX
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Assisted Solution

InteraX earned 400 total points
ID: 18870340
InteraX,

Second reference

TTL             which is the time to live of the RR.  This field is a 32
bit integer in units of seconds, an is primarily used by
resolvers when they cache RRs.  The TTL describes how
long a RR can be cached before it should be discarded.
http://www.faqs.org/rfcs/rfc1034.html

InteraX
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Author Comment

ID: 18870359
wow, thanks a lot for the information. i got pretty good idea!!! I'll increase the points and split among the participants.

-Michael
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