Requirements for a Mechanism Identifying a Name Server Instance
RFC 4892

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Network Working Group                                           S. Woolf
Request for Comments: 4892             Internet Systems Consortium, Inc.
Category: Informational                                        D. Conrad
                                                                   ICANN
                                                               June 2007

    Requirements for a Mechanism Identifying a Name Server Instance

Status of This Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   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 for
   administrators.  Existing ad hoc mechanisms for addressing this need
   have some shortcomings, not the least of which is the lack of prior
   analysis of exactly how such a mechanism should be designed and
   deployed.  This document describes the existing convention used in
   some widely deployed implementations of the DNS protocol, including
   advantages and disadvantages, and discusses some attributes of an
   improved mechanism.

1.  Introduction and Rationale

   Identifying which name server is responding to queries is often
   useful, particularly in attempting to diagnose name server
   difficulties.  This is most obviously useful for authoritative
   nameservers in the attempt to diagnose the source or prevalence of
   inaccurate data, but can also conceivably be useful for caching
   resolvers in similar and other situations.  Furthermore, the ability
   to identify which server is responding to a query has become more
   useful as DNS has become more critical to more Internet users, and as
   network and server deployment topologies have become more complex.

Woolf & Conrad               Informational                      [Page 1]
RFC 4892                        Serverid                       June 2007

   The conventional means for determining which of several possible
   servers is answering a query has traditionally been based on the use
   of the server's IP address as a unique identifier.  However, the
   modern Internet has seen the deployment of various load balancing,
   fault-tolerance, or attack-resistance schemes such as shared use of
   unicast IP addresses as documented in [RFC3258].  An unfortunate side
   effect of these schemes has been to make the use of IP addresses as
   identifiers associated with DNS (or any other) service somewhat
   problematic.  Specifically, multiple dedicated DNS queries may not go
   to the same server even though sent to the same IP address.  Non-DNS
   methods such as ICMP ping, TCP connections, or non-DNS UDP packets
   (such as those generated by tools like "traceroute"), etc., may well
   be even less certain to reach the same server as the one which
   receives the DNS queries.

   There is a well-known and frequently-used technique for determining
   an identity for a nameserver more specific than the possibly-non-
   unique "server that answered the query I sent to IP address A.B.C.D".
   The widespread use of the existing convention suggests a need for a
   documented, interoperable means of querying the identity of a
   nameserver that may be part of an anycast or load-balancing cluster.
   At the same time, however, it also has some drawbacks that argue
   against standardizing it as it's been practiced so far.

2.  Existing Conventions

   For some time, the commonly deployed Berkeley Internet Name Domain
   (BIND) implementation of the DNS protocol suite from the Internet
   Systems Consortium [BIND] has supported a way of identifying a
   particular server via the use of a standards-compliant, if somewhat
   unusual, DNS query.  Specifically, a query to a recent 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.  (The value defaults to the result 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.

   A refinement to the BIND-based mechanism, which dropped the
   implementation-specific label, replaces "BIND." with "SERVER.".  Thus
   the query label to learn the unique name of a server may appear as
   "ID.SERVER.".

   (For reference, the other well-known name used by recent versions of