easy to understand definitions

Sebastian Castro Avila secastro at nic.cl
Wed Mar 23 15:58:41 UTC 2005

On Wed, 23 Mar 2005 09:38:42 -0500, Bob Lockie <bjlockie at lockie.ca> wrote:

> I found the following definitions but I need definitions that are easier
> to understand.
> I do not have my Bind book available.
> #  refresh - How often the slave servers should check the serial number
> on the master for changes.
> # retry - Amount of time a slave should wait before attempting another
> "refresh" after a previous refresh has failed.

I agree with these first two definitions.

> # expire - How long a slave should use it's DNS information without a
> refresh from the master.

How long a slave can answer as an authoritative source without refreshing  
with the master.
When the "expire" timer ends, that server gives "SERVFAIL" for any  
question regarding the domain.

Reach that timer is BAD, so it's recommended to have a high value (2 to 4  

> # minimum - How long a server should cache negative hits (e.g. no such
> domain/host).

Also, how long a server can keep the answer cached.

If you have long values, any change you make will take longer to  
propagate. If you choose a short value, your authoritative servers will  
receive more queries.

Check RFC 1912 (http://www.faqs.org/rfcs/rfc1912.html) for a better  
explanation and some recomendations.

Best Regards

> I don't understand "expire" and "refresh", it would seem that "expire"
> should always be equal to the "refresh" time"?
Sebastian E. Castro Avila             sebastian at nic.cl
Administrador de DNS, NIC Chile
Fono: (2) 9407705                  Fax  : (2) 9407701

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