On 2015-08-28 14:15, Darcy Kevin (FCA) wrote:
As you pointed out (correctly), this isn't an issue which affects anything that goes "on the
wire", e.g. master-slave replication via AXFR/IXFR, since, "on the wire" the TTL is
always included with the RR. It's only an issue for how the zone files are managed on the master.
My opinion: named on the master should reject illegal zone files.
Agreed. Could you please cite where in RFC 2308 $TTL is a MUST, or even
a SHOULD? Or was this made mandatory elsewhere?
RFC 2308 is clear on what should happen after a $TTL directive, but
seems silent on how to handle resource records prior to, or in the
absence of a $TTL directive, but it does note that the "minimum TTL"
field has traditionally had three uses:
First: as a minimum. Result? "is hereby deprecated"
Second: Result? No change in status.
Third: "The remaining of the current meanings, of being the TTL to be
used for negative responses, is the new defined meaning of the SOA
minimum field." -- This almost goes far enough to depreciate the second,
but given the explicit language depreciating the first, I would think
that the author would have used similar language had they intended to
depreciate the second.
The closest we get is section 4, "Where a server does not require RRs to
include the TTL value explicitly, it should provide a mechanism, not
being the value of the MINIMUM field of the SOA record, from which the
missing TTL values are obtained."
That's a "should" (not even a "SHOULD"), but in the absence of this
specified minimum (either by lack of implementation, or lack of
configuration), the SOA MINIMUM field would seem to be better than
failing outright.
It's perhaps only an issue for some homebrew zonefile-creation scripts that were written
a long time ago, and where the administrators have been systematically ignoring the
"no TTL specified; using SOA MINTTL instead" errors in their logs, every time
named loads or reloads the zones.
I'm not suggesting I'm going to start writing or recommending zone files
without a $TTL directive, or that this is even a big deal in the real
world, but I'm struggling to find a case where the absence of a $TTL
directive would result in a zone file being illegal, and so falling back
on the SOA's "minimum" field would seem to be a more sane choice than
making one up or refusing the zone, if only as a nod to the legacy use
of this field.
--
Dave Warren
http://www.hireahit.com/
http://ca.linkedin.com/in/davejwarren
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