Re: repeating records

["D. J. Bernstein" <djb@cr.yp.to>]

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Andreas Gustafsson writes:
> I would certainly want implementers to understand and carefully weigh
> the implications of multiple transmission, such as waste of bandwidth
> and receiver CPU time.  Are you suggesting they should not?

Yes or no: Are you claiming that every DNS implementor, before choosing
to use (for example) BIND 8's strategy of sending glue whenever it's
referenced, _must_ understand and carefully weigh the implications?

That's the definition of ``SHOULD'' in RFC 2119. It's a mechanism to
warn implementors about behaviors that are interoperable but dangerous;
see RFC 2119, section 6. It isn't an excuse for you to have your BIND 9
implementation decisions masquerading as protocol requirements.

Are you next going to claim that people ``SHOULD NOT'' put DNS records
into LDAP? Look at all that wasted bandwidth and CPU time!

As another example, you're wasting tons of bandwidth by using zone
transfers (incremental but not compressed) rather than rsync-over-ssh
(incremental _and_ compressed). Have you understood and carefully
weighed the implications of your poor choice of protocols? How would you
like it if someone said that you ``SHOULD NOT'' use zone transfers?

Andreas Gustafsson writes:
> Incidentally, I found it amusing that the author of RFC2119
> specifically chose limiting retransmissions as the example; although
> he probably had a different kind of retransmission in mind than that
> of transmitting records multiple times in an AXFR, they both cause 
> similar harm in the form of wasted bandwidth.

Wow, are you really this ignorant? The retransmission issue has nothing
to do with optimizing bandwidth use. The retransmission issue is that
momentary network overloads can snowball into nearly complete outages.

If people really are misusing ``SHOULD'' for minor efficiency issues
(misinterpreting ``harm'' in section 6 of RFC 2119), we're going to need
a new word to point out real dangers such as over-eager retransmission.

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago



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