North American Network Operators Group

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Re: dns based loadbalancing/failover

  • From: Paul Vixie
  • Date: Sun Oct 07 13:05:01 2001

> The way to go about this is to see if breaking existing practice will break
> current implementations and plausible future implementations.

Allow me to apologize, once again, to Microsoft.  In the NT 3.5.1 resource kit
they shipped a DNS server which had to do its zone transfers one record per
message since "existing practice" and "current implementations" meant BIND4
which knew no other way.  Fortunately we didn't write a BCP describing BIND4's
deviant behaviour, but rather, fixed it in BIND8 and beyond.

> > If that's not the case, though, consider that a correct implementation of
> > DNS would be within its rights to take note of the "same serial number but
> > incoherent answers" condition and declare the zone unreachable.  I'm not
> 
> Would be pretty silly, and overstepping the robustness principle.

Whether behaviour is robust enough to be called a BCP or not is fodder for a
detailed analysis amongst people who *want* to study and debate such things.
That mailing list, for DNS, is called namedroppers@ops.ietf.org.  (Not NANOG.)

> So by your logic, by making sure that the serial numbers never match, we
> would 'unbreak' the situation? Seems like a step in the wrong direction.

There is, simply is and we're not going to argue about it, an identity mapping
between a zone's contents and a zone's serial number.  If you don't like that
then you should find a way to change it.  Which direction is "wrong" is better
discussed on namedroppers@ops.ietf.org than here.