RFC 3197 (rfc3197) - Page 2 of 5

Applicability Statement for DNS MIB Extensions

RFC 3197      Applicability Statement - DNS MIB Extensions November 2001


   of concerns with the network management directorate, but the WG
   resisted every attempt to remove any of these variables.  In the end,
   large portions of the MIB extensions were moved into optional groups
   in an attempt to get the required subset down to a manageable size.

   The DNS Server and Resolver MIB extensions were one of the first
   attempts to write MIB extensions for a protocol usually considered to
   be at the application layer.  Fairly early on it became clear that,
   while it was certainly possible to write MIB extensions for DNS, the
   SMI was not really designed with this sort of thing in mind.  A case
   in point was the attempt to provide direct indexing into the caches
   in the resolver MIB extensions: while arguably the only sane way to
   do this for a large cache, this required much more complex indexing
   clauses than is usual, and ended up running into known length limits
   for object identifiers in some SNMP implementations.

   Furthermore, the lack of either real proxy MIB support in SNMP
   managers or a standard subagent protocol meant that there was no
   reasonable way to implement the MIB extensions in the dominant
   implementation (BIND).  When the AgentX subagent protocol was
   developed a few years later, we initially hoped that this would
   finally clear the way for an implementation of the DNS MIB
   extensions, but by the time AgentX was a viable protocol it had
   become clear that nobody really wanted to implement these MIB
   extensions.

   Finally, the MIB extensions took much too long to produce.  In
   retrospect, this should have been a clear warning sign, particularly
   when the WG had clearly become so tired of the project that the
   authors found it impossible to elicit any comments whatsoever on the
   documents.

2. Lessons

   Observations based on the preceding list of mistakes, for the benefit
   of anyone else who ever attempts to write DNS MIB extensions again:

   -  Define a clear set of goals before writing any MIB extensions.
      Know who the constituency is and make sure that what you write
      solves their problem.

   -  Keep the MIB extensions short, and don't add variables just
      because somebody in the WG thinks they'd be a cool thing to
      measure.

   -  If some portion of the task seems to be very hard to do within the
      SMI, that's a strong hint that SNMP is not the right tool for
      whatever it is that you're trying to do.



Austein                      Informational