Why is $TTL required for the root hints?

[Barry Margolin]

In article <9omk5a$ap4 at pub3.rc.vix.com>,
Jesper Dybdal  <jdunet at u6.dybdal.dk> wrote:
>But the root hints are not real DNS records, only hints - does it cache the
>hints themselves (in the sense of keeping them and sending them to clients) at
>all?
>
>My impression is that the root hints are only used to query servers for the
>real root NS and A records, which are then cached (with their real TTLs), and
>that the root hints themselves are never used directly in responses to
>queries.  Is that wrong?

Until a reply is received to one of those root queries, the hints are saved
in the cache.  And when the TTLs of the real root server entries expire, I
expect it reverts back to the hint records so that it can query a root
server again.

>Let me rephrase my original question: does it ever make any externally
>noticable difference whether the root hints TTL is small or large?  And if so,
>what value is a good value for that TTL?

Assuming my explanation above is correct, the hint TTLs needs to be longer
than the real root TTLs.

The named.root file from ftp.rs.internic.net has TTL=3600000 (1,000 hours,
which is about 41 days).  Why don't you just use that?

-- 
Barry Margolin, barmar at genuity.net
Genuity, Woburn, MA
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