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Network Working Group                                         M. Andrews
Internet-Draft                                                       ISC
Expires: November 22, 2013                                  May 21, 2013


   A Common Operational Problem in DNS Servers - Failure To Respond.
               draft-andrews-dns-no-response-issue-00.txt

Abstract

   The DNS is a query / response protocol.  Failure to respond to
   queries causes both immediate operational problems and long term
   problems with protocol development.

   This document will identify a number of common classes of queries
   that some servers fail to respond too.  This document will also
   suggest procedures for TLD and other similar zone operators to apply
   to reduce / eliminate the problem.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 22, 2013.

Copyright Notice

   Copyright (c) 2013 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of



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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Common queries class that result in non responses.  . . . . . . 3
     2.1.  EDNS Queries  . . . . . . . . . . . . . . . . . . . . . . . 3
     2.2.  Unknown / Unsupported Type Queries  . . . . . . . . . . . . 4
   3.  Remediating . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   4.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 5






































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1.  Introduction

   The DNS [RFC1034], [RFC1035] is a query / response protocol.  Failure
   to respond to queries causes both immediate operational problems and
   long term problems with protocol development.

   Failure to respond to a query is indistinguishable from a packet loss
   without doing a analysis of query response patterns and results in
   unnecessary additional queries being made by DNS clients and
   unnecessary delays being introduced to the resolution process.

   Allowing servers which fail to respond to queries to remain in the
   DNS hierarchy for extended periods results in developers being afraid
   to deploy new type codes.  Such servers need to be identified and
   corrected / replaced.

   The DNS has response codes that cover almost any conceivable query
   response.  A nameserver should be able to respond to any conceivable
   query using them.

   Unless a nameserver is under attack, it should respond to all queries
   directed to it as a result of following delegations.  Additionally
   code should not assume that there isn't a delegation to the server
   even if it is not configured to serve the zone.  Broken delegation
   are a common occurrence in the DNS and receiving queries for zones
   that you are not configured for is not a necessarily a indication
   that you are under attack.


2.  Common queries class that result in non responses.

   There are two common query class that result in non responses today.
   These are EDNS [RFC2671] queries and queries for unknown
   (unallocated) or unsupported types.

2.1.  EDNS Queries

   Identifying servers that fail to respond to EDNS queries can be done
   by first identifying that the server responds to regular DNS queries
   then making a series otherwise identical responses using EDNS, then
   making the original query again.  A series of EDNS queries is needed
   as at least one DNS implementation responds to the first EDNS query
   with FORMERR but fails to respond to subsequent queries from the same
   address for a period until a regular DNS query is made.

   If the server responds to the first and last queries but fails to
   respond to most or all of the EDNS queries it is probably faulty.
   The test should be repeated a number of times to eliminate the likely



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   hood of a false positive due to packet loss.

2.2.  Unknown / Unsupported Type Queries

   Identifying servers that fail to respond to unknown or unsupported
   types can be done by making a initial DNS query for a A record,
   making a number of queries for unallocated type, them making a query
   for a A record again.  IANA maintains a registry of allocated types.

   If the server responds to the first and last queries but fails to
   respond to the queries for the unallocated type it is probably
   faulty.  The test should be repeated a number of times to eliminate
   the likely hood of a false positive due to packet loss.


3.  Remediating

   While the first step in remediating this problem is to get the
   offending nameserver code corrected, there is a very long tail
   problem with DNS servers in that it can often take over a decade
   between the code being corrected and a nameserver being upgraded with
   corrected code.  With that in mind it is requested that TLD, and
   other similar zone operators, take steps to identify and inform their
   customers, directly or indirectly through registrars, that they are
   running such servers and that the customers need to correct the
   problem.

   TLD operators should construct a list of servers child zones are
   delegated to along with a delegated zone name.  This name shall be
   the query name used to test the server as it is supposed to exist.

   For each server the TLD operator shall make a SOA query the delegated
   zone name.  This should result in the SOA record being returned in
   the answer section.  If the SOA record is not return but some other
   response is returned this is a indication of a bad delegation and the
   TLD operator should take whatever steps it normally takes to rectify
   a bad delegation.  If more that one zone is delegated to the server
   it should choose another zone until it finds a zone which responds
   correctly or it exhausts the list of zones delegated to the server.

   If it fails to get a response to a SOA query the TLD operator should
   make a A query as some nameservers fail to respond to SOA queries but
   respond to A queries.  If it gets no response to the A query another
   delegated zone should be queried for as some nameservers fail to
   respond to zones they are not configured for.  If subsequent queries
   find a responding zone all delegation to this server need to be
   checked and rectified using the TLD's normal procedures.




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   Having identified a working <server, query name> tuple the TLD
   operator should now check that the server responds to both EDNS and
   unknown query type tests as described above.  If the TLD operator
   finds that server fails either or both tests, the TLD operator shall
   take steps to inform the operator of the server that they are running
   a fault nameserver and that they need to take steps to correct the
   matter.  The TLD operator shall also record the <server, query name>
   for followup testing.

   If repeated attempts to inform and get the customer to correct /
   replace the fault server are unsuccessful the TLD operator shall
   remove all delegations to said server from the zone.


4.  Normative References

   [RFC1034]  Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES",
              STD 13, RFC 1034, November 1987.

   [RFC1035]  Mockapetris, P., "DOMAIN NAMES - IMPLEMENTATION AND
              SPECIFICATION", STD 13, RFC 1035, November 1987.

   [RFC2671]  Vixie, P., "Extension Mechanisms for DNS (EDNS0)",
              RFC 2671, August 1999.


Author's Address

   M. Andrews
   Internet Systems Consortium
   950 Charter Street
   Redwood City, CA  94063
   US

   Email: marka@isc.org
















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