DNS upgrade ($TTL qustion)

[Joseph S D Yao]

>    I see this question alot.  And I've seen some very brief answers that
> have left me sometimes more confused just when I though I was finally
> catching on :-(   I've looked through the "DNS and BIND 3rd Ed." for
> information and *examples* on the use of the $TTL directive and found
> nothing.  Okay, I'm stupid... 
> 
>    Checked the index in the back.  Under T for TTL it lists some pages.
> Read 'em. Still not clear.  Looked under the 'symbols' at the beginning of
> the index.  '$' is not even listed...  Okay, where in the 480 pages do I
> find information about this puppy?

Given that the RFC and BIND 8.2 came out AFTER the book, there is no
wonder that you won't find it in there.  It isn't.  I have secret,
private information that Cricket is writing a 4th Ed. [i.e., he
announced it publicly in this forum ;-)].

As has been published before several times in this forum:

> Date: Wed, 8 Sep 1999 13:36:44 -0700 (PDT)
> From: chris cariffe <cariffec at zippy.riscorian.com>
> Subject: Re: TTL directive
> 
> $TTL 86400
> 
> located above the SOA record
> 
> -chris

OR

> From: Joseph S D Yao <jsdy at cospo.osis.gov>
> Subject: Re: Setting up re-direction
> Date: Fri, 3 Sep 1999 12:40:32 -0400 (EDT)
> 
> 	$ORIGIN my.bought.domain
> 	$TTL	1d
> 	@	IN  SOA		... (...)
> 		IN  NS		...
> 	web		IN  A		254.253.252.251
> 	www		IN  CNAME	web.my.bought.domain.
> 	www2		IN  CNAME	www.freepages.com.

OR

> Date: Tue, 31 Aug 1999 16:39:03 -0500
> From: Morgan Sarges <blip at actioni.net>
> Subject: Re: Last question?
> 
> $ORIGIN actioni.net.
> $TTL 86400
> actioni.net.            IN      SOA     bugs.actioni.net. root.actioni.net. (
>                         36
>                         10800
>                         3600
>                         604800
>                         86400 )

That's the syntax.

Semantics: the fifth number in the SOA used to refer to the default
TTL.  Over time, it acquired three separate meanings, which I forget -
they are listed in the relevant RFC, which I also forget.  But one was
the default TTL for following resource records, and one was the TTL for
negative caching information.

The $TTL now gives the default TTL for following resource records.  As
with all statements that start with '$', it's sort of like a
pre-processor statement: it affects following statements, but it is not
itself something that is remembered once parsed and read in.  The fifth
element of the SOA is now supposedly just the negative caching TTL.  Of
course, if there is no $TTL line before the SOA, then 'named' will
complain and use the fifth SOA element for that purpose.

For now.

Does this help?

--
Joe Yao				jsdy at cospo.osis.gov - Joseph S. D. Yao
COSPO/OSIS Computer Support					EMT-B
-----------------------------------------------------------------------
This message is not an official statement of COSPO policies.