DNS Negative Caching

Barry Margolin barmar at alum.mit.edu
Sat Aug 29 00:27:46 UTC 2015


In article <mailman.2604.1440796547.26362.bind-users at lists.isc.org>,
 "Darcy Kevin (FCA)" <kevin.darcy at fcagroup.com> wrote:

> Negative-caching TTL and regular TTL have little to do with each other; it's 
> not a reasonable assumption that one should stand in as a default for the 
> other.

True, but that's water long under the bridge.

Note that if a server is authoritative-only, caching is mostly 
irrelevant, so the negative cache TTL doesn't much apply. In this case, 
the SOA Minimum is just being used as the default TTL.

> My opinion: named on the master should reject illegal zone files.

As far as I can tell, nothing in RFC 2308 says that $TTL is required. I 
don't even see a SHOULD, let alone a MUST. Is there a later RFC that 
adds this requirement? If not, then a zone file without $TTL is legal. 
And for backward compatibility, it should continue to use the SOA 
Minimum field as the default TTL.

-- 
Barry Margolin
Arlington, MA


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