INTERNET-DRAFT                                            David
Network Working Group                                           S. Woolf
Internet-Draft                         Internet Systems Consortium, Inc.
Expires: January 16, 2005                                      D. Conrad
                                                           Nominum, Inc.
                                                        November, 2002
                                                           July 18, 2004

               Identifying an Authoritative Name Server `Server

Status of this Memo

   This document is an Internet-Draft and is in full conformance with subject to all provisions
   of Section 10 section 3 of RFC 3667.  By submitting this Internet-Draft, each
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   which he or she become aware will be disclosed, in accordance with
   RFC 3668.

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Copyright Notice

   Copyright (C) The Internet Society (2004).  All Rights Reserved.


   With the increased use of DNS anycast, load balancing, and other
   mechanisms allowing more than one DNS name server to share a single
   IP address, it is sometimes difficult to tell which of a pool of name
   servers has answered a particular query.  A standardized mechanism to
   determine the identity of a name server responding to a particular
   query would be useful, particularly as a diagnostic aid.  Existing ad
   hoc mechanisms for addressing this concern are not adequate.  This
   document describes an identification convention
   used in one widely deployed implementation of attempts to describe the DNS protocol common ad hoc solution to this
   problem, including its advantages and disadvantasges, and
   proposes a slight modification to that convention aimed at addressing
   some implementation concerns.
   characterize an improved mechanism.

1.  Introduction


   With the identity increased use of the DNS anycast, load balancing, and other
   mechanisms allowing more than one DNS name server responding to share a query single
   IP address, it is sometimes difficult to tell which of a pool of name
   servers has
   become more complex due primarily answered a particular query.  A standardized mechanism to
   determine the proliferation identity of various
   load balancing techniques.  This document describes a convention used
   by one particular DNS name server implementation responding to provide identifying
   information and proposes a slight modification to that convention to
   address concerns regarding implementation neutrality.

   Note that this document makes no value judgements particular
   query would be useful, particularly as to whether or a diagnostic aid.

   Unfortunately, existing ad-hoc mechanisms for providing such
   identification have some shortcomings, not the convention in current use least of which is good or bad; it merely documents the covention's existence and proposes a slight redefinition
   lack of prior analysis of exactly how such a mechanism should be
   designed and deployed.  This document describes the existing
   convention to address non-technical used in one widely deployed implementation concerns. of the DNS
   protocol and discusses requirements for an improved solution to the

2.  Rationale

   Identifying which name server is responding to queries is often
   useful, particularly in attempting to diagnose name server
   difficulties.  However, relying on the IP address of the name server
   has become more problematic due the deployment of various load
   balancing solutions, including the use of shared unicast addresses as
   documented in [RFC3258].

   An unfortunate side effect of these load balancing solutions is that
   traditional methods of determining which server is responding can be
   unreliable.  Specifically, non-DNS methods such as ICMP ping, TCP
   connections, or non-DNS UDP packets (e.g., as generated by tools such
   as "traceroute"), etc., can end up going to a different server than
   that which receives the DNS queries.

   This proposal makes

   The widespread use of the existing convention suggests a need for a
   documented, interoperable means of querying the assumption identity of a
   nameserver that may be part of an identification mechanism
   that relies on the DNS protocol is more likely to be successful
   (although not guaranteed) in going to anycast or load-balancing cluster.
   At the same machine time, however, it also has some drawbacks that argue
   against standardizing it as a "normal"
   DNS query. it's been practiced so far.

3. Historical  Existing Conventions

   Recent versions of the commonly deployed Berkeley Internet Name
   Domain implementation of the DNS protocol suite from the Internet
   Software Consortium [BIND] support a way of identifying a particular
   server via the use of a standard, if somewhat unusual, DNS query.
   Specifically, a query to a late model BIND server for a TXT resource
   record in class 3 (CHAOS) for the domain name "HOSTNAME.BIND." will
   return a string that can be configured by the name server
   administrator to provide a unique identifier for the responding
   server (defaulting to the value of a gethostname() call).  This
   mechanism, which is an extension of the BIND convention of using
   CHAOS class TXT RR queries to sub-domains of the "BIND." domain for
   version information, has been copied by several name server vendors.

   For reference, the other well-known name used by recent versions of
   BIND within the CHAOS class "BIND." domain is "VERSION.BIND."  A
   query for a TXT RR for this name will return an administratively re-
   definable string which defaults to the version of the server


3.1  Advantages

   There are several valuable attributes to this mechanism, which
   account for its usefulness.
   1.  This mechanism is within the DNS protocol itself.  An Implementation Neutral Convention

   The previously described use of
       identification mechanism that relies on the CHAOS class "BIND." domain has
   (rightly) been viewed by many implementors as DNS protocol is more
       likely to be successful (although not being standardized
   nor being implementation neutral.  As such, a standard mechanism guaranteed) in going to
   identify a particular machine among a shared unicast set of machines
   serving the
       same DNS data does not currently exist.

   Since machine as a name server conforming "normal" DNS query.
   2.  It is simple to [RFC1034] and [RFC1035] should
   support the CHAOS class configure.  An administrator can easily turn on
       this feature and control the use results of TXT resource record queries in
   the CHAOS class to derive information about a name server has been
   used in several independent name server implementations, the quickest
   way of supporting relevant query.
   3.  It allows the identification administrator complete control of a particular name server what information
       is given out in the response, minimizing passive leakage of a set of name servers all sharing
       implementation or configuration details.  Such details are often
       considered sensitive by infrastructure operators.

3.2  Disadvantages

   At the same unicast prefix would
   likely be time, there are some forbidding drawbacks to standardize on the BIND convention, albeit with a slight
   VERSION.BIND mechanism that argue against standardizing it as it
   currently operates.
   1.  It requires an additional query to address implementation neutrality concerns.

   The convention proposed here simply redefines correlate between the top level CHAOS
   domain answer
       to be "SERVER." instead a DNS query under normal conditions and the supposed identity
       of "BIND.".  Since using the actual
   hostname may be considered server receiving the query.  There are a number of
       situations in which this simply isn't reliable.
   2.  It reserves an information leakage security risk, entire class in the DNS (CHAOS) for what amounts
       to one zone.  While CHAOS class is defined in [RFC1034] and
       [RFC1035], it's not clear that supporting it solely for this
       purpose is a good use of the actual hostname namespace or of the server implementation
   3.  It is discouraged and instead a
   unique per-server identifier should be used.  As the implementation specific.  BIND convention
   of "HOSTNAME" implies is one DNS implementation.
       At the use time of this writing, it is probably the most prevalent,
       for authoritative servers anyway.  This does not justify
       standardizing on its ad hoc solution to a hostname, problem shared across
       many operators and implementors.

   The first of the domain name
   "ID.SERVER" listed disadvantages is proposed.  That is, a TXT RR query for "ID.SERVER." in technically the CHAOS class will return most
   serious.  It argues for an administratively defined string that
   can be used attempt to differentiate among multiple servers.

   To make this convention useful, DNS operators wishing to identify
   their servers uniquely MUST, for EACH server, put design a unique string for good answer to the RDATA
   problem that "I need to know what nameserver is answering my
   queries", not simply a convenient one.

4.  Characteristics of the TXT record associated with the "ID.SERVER." domain
   in class CHAOS.  For example, given two machines "" an Implementation Neutral Convention

   The discussion above of advantages and
   "" that receive DNS queries at disadvantages to the same IP address,
   HOSTNAME.BIND mechanism suggest some requirements for a better
   solution to the
   name server administrator could include

        ID   CH   TXT  "a"

   in the appropriate zone file on machine "" and

        ID   CH   TXT  "b"

   in the appropriate zone file on machine "".

   Queries identification problem.  These are summarized
   here as guidelines for TXT RRs of "id.server" in class CHAOS any effort to provide appropriate protocol
   1.  The mechanism adopted MUST be in-band for the IP address
   serving both "" and "" should return "a" or
   "b" depending on which machine DNS protocol.  That
       is, it needs to allow the query was routed.

   Implementors MUST provide a way to disable returning this for the server's identifying
   information.  Implementors
       information to be part of a normal, operational query.  It SHOULD provide
       also permit a way to limit who can separate, dedicated query for the server's
       identifying information.
   2.  The use of new mechanism should not require dedicated namespaces or
       other names in reserved values outside of the CHAOS class "SERVER." domain are beyond existing protocol mechanisms
       for these, i.e.  the scope of this document.

IANA Considerations

   The "SERVER." domain in OPT pseudo-RR.
   3.  Support for the CHAOS class should identification functionality SHOULD be reserved by IANA easy to
       implement and a registry easy to enable.  It MUST be easy to disable and
       SHOULD lend itself to access controls on who can query for it.
   4.  It should be created that reserves the "ID" name.  In possible to return a unique identifier for a server
       without requiring the
   future, requests exposure of information that may be submitted
       non-public and considered sensitive by the operator, such as a
       hostname or unicast IP address maintained for other sub-domains administrative
   5.  The identification mechanism SHOULD NOT be

5.  IANA Considerations

   This document proposes no specific IANA action.  Protocol extensions,
   if any, to meet the requirements described are out of "SERVER.",
   e.g., "VERSION.SERVER." scope for this
   document.  Should such extensions be specified and adopted by normal
   IETF process, the IANA should take specification will include appropriate action. guidance to

6.  Security Considerations

   Providing identifying information as to which server is responding
   can be seen as information leakage and thus a security risk.  It may
   be appropriate  This
   motivates the suggestion above that a new mechanism for server
   identification allow the administrator to disable the functionality
   altogether or partially restrict who can query for availability of the "ID.SERVER." domain.
   Filtering on source data.  It also
   suggests that the serverid data should not be readily correlated with
   a hostname or unicast IP address would that may be one way in which restrictions considered private to
   the nameserver operator's management infrastructure.

   Propagation of protocol or service meta-data can be applied.

   The identifer returned via an "ID.SERVER." query SHOULD NOT contain sometimes expose the hostname
   application to denial of service or other information that could attack.  As DNS is a
   critically important infrastructure service for the production
   Internet, extra care needs to be considered sensitive. taken against this risk for
   designers, implementors, and operators of a new mechanism for server

7.  Acknowledgements

   The technique for host identification documented here derive from
   practices was initially
   implemented by Paul Vixie of the Internet Software Consortium in the
   Berkeley Internet Name Domain Daemon package.  Useful
   comments  Comments and questions on
   earlier drafts were provided by Bob Halley, Brian Wellington, Andreas
   Gustafsson, Ted Hardie, Chris Yarnell, Randy Bush, and members of the
   ICANN Root Server System Advisory Council.  Additional
   explanatory information provided due to questions received Committee.  The newest draft takes
   a significantly different direction from Randy


   [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities",
   RFC 1034, November 1987.

   [RFC1035] Mockapetris, P., "Domain Names - Implementation and
   Specifications", RFC 1035, November 1987.

   [RFC2119] Bradner, S., "Key words for use in RFCs previous versions, owing to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3258] Hardie, T., "Distributing Authoritative Name Servers via
   Shared Unicast Addresses", RFC 3258, April, 2002.

Author's Address
   David Conrad
   Nominum, Inc.
   2385 Bay Road
   Redwood City, CA 94063

   Phone: +1 650 381 6003
   Fax:   +1 650 381 6055

Full Copyright
   discussion among contributors to the DNSOP working group and others,
   particularly Olafur Gudmundsson, Ed Lewis, Bill Manning, Sam Weiler,
   and Rob Austein.

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