Re: RFC 2182 considered harmful

[Edward Lewis <lewis@tislabs.com>]

At 12:18 AM -0500 2/4/00, D. J. Bernstein wrote:
>RFC 2182 has frightened many administrators into obtaining unnecessary
>third-party DNS service. It says that this ``must'' be done and that it
>is ``important'' and that the alternative---which it admits is easier
>for administrators---is ``not a good policy''; but these bold claims are
>not justified by the facts.

Since I am not sure what is prompting this thread, I went back to the
original message and the RFC.

The RFC is a BCP, not a standard (STD).  The document does not claim
conformance with RFC 2119, which gives meaning to "MUST," etc., as terms of
requrements.  Given the BCP status and no claim that RFC 2119 applies, I
think you are interepreting the document in the wrong way.  This is a
recommendation, not a protocol requirement.

Just to over explain my point, here is one use of the word "must" that
addresses the paragraph I repeated from your message.

#3.1. Selecting Secondary Servers
...
#   Secondary servers must be placed at both topologically and
#   geographically dispersed locations on the Internet, to minimise the
#   likelihood of a single failure disabling all of them.

"Must" means that to achieve the ability to withstand a single failure, the
servers have to be dispersed.  This makes sense to me.

The word "must" appears just 5 more times in the document.  In section 4.
must is used to define a sequence of steps needed to arrive at a decision.
In 4.3, the word must is used to describe actions needed "to avoid these
problems."  In section 5, the use of the word must is a bit questionable
because a phrase like "to achieve reliability" is missing.  This is a
quibble, the sentance is shown below.  Finally, in section 7, the word must
is used to illustrate the operation of the protocol.

# 5. How many secondaries?
#
#   It is recommended that three servers be provided for most
#   organisation level zones, with at least one which must be well
#   removed from the others.  For zones where even higher reliability is
#   required, four, or even five, servers may be desirable.  Two, or ...

"Well removed" could be interpreted as being "on another machine" though.

After going through this, I wouldn't agree that the document is "harmful."

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Edward Lewis                                                NAI Labs
Phone: +1 443-259-2352                      Email: lewis@tislabs.com

"Trying is the first step to failure." - Homer Simpson
"No! Try not. Do... or do not. There is no try." - Yoda
"It takes years of training to know when to do nothing" - Dogbert 1/21/00

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