draft-ietf-dnsop-serverid-01.txt   draft-ietf-dnsop-serverid-02.txt 
INTERNET-DRAFT David Conrad Network Working Group S. Woolf
draft-ietf-dnsop-serverid-01.txt Nominum, Inc. Internet-Draft Internet Systems Consortium, Inc.
November, 2002 Expires: January 16, 2005 D. Conrad
Nominum, Inc.
July 18, 2004
Identifying an Authoritative Name Server Identifying an Authoritative Name `Server
draft-ietf-dnsop-serverid-02
Status of this Memo Status of this Memo
This document is an Internet-Draft and is in full conformance with This document is an Internet-Draft and is subject to all provisions
all provisions of Section 10 of RFC2026. of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as
Drafts. Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at http://
http://www.ietf.org/ietf/1id-abstracts.txt www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html. http://www.ietf.org/shadow.html.
This Internet-Draft will expire on January 16, 2005.
Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract Abstract
A standardized mechanism to determine the identity of a name server With the increased use of DNS anycast, load balancing, and other
responding to a particular query would be useful, particularly as a mechanisms allowing more than one DNS name server to share a single
diagnostic aid. This document describes an identification convention IP address, it is sometimes difficult to tell which of a pool of name
used in one widely deployed implementation of the DNS protocol and servers has answered a particular query. A standardized mechanism to
proposes a slight modification to that convention aimed at addressing determine the identity of a name server responding to a particular
some implementation concerns. query would be useful, particularly as a diagnostic aid. Existing ad
hoc mechanisms for addressing this concern are not adequate. This
document attempts to describe the common ad hoc solution to this
problem, including its advantages and disadvantasges, and to
characterize an improved mechanism.
1. Introduction 1. Introduction
Determining the identity of the name server responding to a query has With the increased use of DNS anycast, load balancing, and other
become more complex due primarily to the proliferation of various mechanisms allowing more than one DNS name server to share a single
load balancing techniques. This document describes a convention used IP address, it is sometimes difficult to tell which of a pool of name
by one particular DNS server implementation to provide identifying servers has answered a particular query. A standardized mechanism to
information and proposes a slight modification to that convention to determine the identity of a name server responding to a particular
address concerns regarding implementation neutrality. query would be useful, particularly as a diagnostic aid.
Note that this document makes no value judgements as to whether or Unfortunately, existing ad-hoc mechanisms for providing such
not the convention in current use is good or bad; it merely documents identification have some shortcomings, not the least of which is the
the covention's existence and proposes a slight redefinition of the lack of prior analysis of exactly how such a mechanism should be
convention to address non-technical implementation concerns. designed and deployed. This document describes the existing
convention used in one widely deployed implementation of the DNS
protocol and discusses requirements for an improved solution to the
problem.
2. Rationale 2. Rationale
Identifying which name server is responding to queries is often Identifying which name server is responding to queries is often
useful, particularly in attempting to diagnose name server useful, particularly in attempting to diagnose name server
difficulties. However, relying on the IP address of the name server difficulties. However, relying on the IP address of the name server
has become more problematic due the deployment of various load has become more problematic due the deployment of various load
balancing solutions, including the use of shared unicast addresses as balancing solutions, including the use of shared unicast addresses as
documented in [RFC3258]. documented in [RFC3258].
An unfortunate side effect of these load balancing solutions is that An unfortunate side effect of these load balancing solutions is that
traditional methods of determining which server is responding can be traditional methods of determining which server is responding can be
unreliable. Specifically, non-DNS methods such as ICMP ping, TCP unreliable. Specifically, non-DNS methods such as ICMP ping, TCP
connections, or non-DNS UDP packets (e.g., as generated by tools such 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 as "traceroute"), etc., can end up going to a different server than
that which receives the DNS queries. that which receives the DNS queries.
This proposal makes the assumption that an identification mechanism The widespread use of the existing convention suggests a need for a
that relies on the DNS protocol is more likely to be successful documented, interoperable means of querying the identity of a
(although not guaranteed) in going to the same machine as a "normal" nameserver that may be part of an anycast or load-balancing cluster.
DNS query. At the same time, however, it also has some drawbacks that argue
against standardizing it as it's been practiced so far.
3. Historical Conventions 3. Existing Conventions
Recent versions of the commonly deployed Berkeley Internet Name Recent versions of the commonly deployed Berkeley Internet Name
Domain implementation of the DNS protocol suite from the Internet Domain implementation of the DNS protocol suite from the Internet
Software Consortium [BIND] support a way of identifying a particular Software Consortium [BIND] support a way of identifying a particular
server via the use of a standard, if somewhat unusual, DNS query. 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 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 record in class 3 (CHAOS) for the domain name "HOSTNAME.BIND." will
return a string that can be configured by the name server return a string that can be configured by the name server
administrator to provide a unique identifier for the responding administrator to provide a unique identifier for the responding
server (defaulting to the value of a gethostname() call). This server (defaulting to the value of a gethostname() call). This
mechanism, which is an extension of the BIND convention of using mechanism, which is an extension of the BIND convention of using
CHAOS class TXT RR queries to sub-domains of the "BIND." domain for CHAOS class TXT RR queries to sub-domains of the "BIND." domain for
version information, has been copied by several name server vendors. version information, has been copied by several name server vendors.
For reference, the other well-known name used by recent versions of For reference, the other well-known name used by recent versions of
BIND within the CHAOS class "BIND." domain is "VERSION.BIND." A BIND within the CHAOS class "BIND." domain is "VERSION.BIND." A
query for a TXT RR for this name will return an administratively re- query for a TXT RR for this name will return an administratively re-
definable string which defaults to the version of the server definable string which defaults to the version of the server
responding. responding.
4. An Implementation Neutral Convention 3.1 Advantages
The previously described use of the CHAOS class "BIND." domain has
(rightly) been viewed by many implementors as not being standardized
nor being implementation neutral. As such, a standard mechanism to
identify a particular machine among a shared unicast set of machines
serving the same DNS data does not currently exist.
Since a name server conforming to [RFC1034] and [RFC1035] should
support the CHAOS class and the use 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 the identification of a particular name server out
of a set of name servers all sharing the same unicast prefix would
likely be to standardize on the BIND convention, albeit with a slight
modification to address implementation neutrality concerns.
The convention proposed here simply redefines the top level CHAOS
domain to be "SERVER." instead of "BIND.". Since using the actual
hostname may be considered an information leakage security risk, the
use of the actual hostname of the server is discouraged and instead a
unique per-server identifier should be used. As the BIND convention
of "HOSTNAME" implies the use of a hostname, the domain name
"ID.SERVER" is proposed. That is, a TXT RR query for "ID.SERVER." in
the CHAOS class will return an administratively defined string that
can be used to differentiate among multiple servers.
To make this convention useful, DNS operators wishing to identify
their servers uniquely MUST, for EACH server, put a unique string for
the RDATA of the TXT record associated with the "ID.SERVER." domain
in class CHAOS. For example, given two machines "a.example.com" and
"b.example.com" that receive DNS queries at the same IP address, the
name server administrator could include
$ORIGIN SERVER.
ID CH TXT "a"
in the appropriate zone file on machine "a.example.com" and There are several valuable attributes to this mechanism, which
account for its usefulness.
1. This mechanism is within the DNS protocol itself. An
identification mechanism that relies on the DNS protocol is more
likely to be successful (although not guaranteed) in going to the
same machine as a "normal" DNS query.
2. It is simple to configure. An administrator can easily turn on
this feature and control the results of the relevant query.
3. It allows the administrator complete control of what information
is given out in the response, minimizing passive leakage of
implementation or configuration details. Such details are often
considered sensitive by infrastructure operators.
$ORIGIN SERVER. 3.2 Disadvantages
ID CH TXT "b"
in the appropriate zone file on machine "b.example.com". At the same time, there are some forbidding drawbacks to the
VERSION.BIND mechanism that argue against standardizing it as it
currently operates.
1. It requires an additional query to correlate between the answer
to a DNS query under normal conditions and the supposed identity
of the server receiving the query. There are a number of
situations in which this simply isn't reliable.
2. It reserves an 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 namespace or of implementation
effort.
3. It is implementation specific. BIND is one DNS implementation.
At the 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 problem shared across
many operators and implementors.
Queries for TXT RRs of "id.server" in class CHAOS to the IP address The first of the listed disadvantages is technically the most
serving both "a.example.com" and "b.example.com" should return "a" or serious. It argues for an attempt to design a good answer to the
"b" depending on which machine the query was routed. problem that "I need to know what nameserver is answering my
queries", not simply a convenient one.
Implementors MUST provide a way to disable returning this identifying 4. Characteristics of an Implementation Neutral Convention
information. Implementors SHOULD provide a way to limit who can
query for the identifying information.
The use of other names in the CHAOS class "SERVER." domain are beyond The discussion above of advantages and disadvantages to the
the scope of this document. HOSTNAME.BIND mechanism suggest some requirements for a better
solution to the server identification problem. These are summarized
here as guidelines for any effort to provide appropriate protocol
extensions:
1. The mechanism adopted MUST be in-band for the DNS protocol. That
is, it needs to allow the query for the server's identifying
information to be part of a normal, operational query. It SHOULD
also permit a separate, dedicated query for the server's
identifying information.
2. The new mechanism should not require dedicated namespaces or
other reserved values outside of the existing protocol mechanisms
for these, i.e. the OPT pseudo-RR.
3. Support for the identification functionality SHOULD be easy to
implement and 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 possible to return a unique identifier for a server
without requiring the exposure of information that may be
non-public and considered sensitive by the operator, such as a
hostname or unicast IP address maintained for administrative
purposes.
5. The identification mechanism SHOULD NOT be
implementation-specific.
IANA Considerations 5. IANA Considerations
The "SERVER." domain in the CHAOS class should be reserved by IANA This document proposes no specific IANA action. Protocol extensions,
and a registry should be created that reserves the "ID" name. In the if any, to meet the requirements described are out of scope for this
future, requests may be submitted for other sub-domains of "SERVER.", document. Should such extensions be specified and adopted by normal
e.g., "VERSION.SERVER." and the IANA should take appropriate action. IETF process, the specification will include appropriate guidance to
IANA.
Security Considerations 6. Security Considerations
Providing identifying information as to which server is responding Providing identifying information as to which server is responding
can be seen as information leakage and thus a security risk. It may can be seen as information leakage and thus a security risk. This
be appropriate to restrict who can query for the "ID.SERVER." domain. motivates the suggestion above that a new mechanism for server
Filtering on source address would be one way in which restrictions identification allow the administrator to disable the functionality
can be applied. altogether or partially restrict availability of the data. It also
suggests that the serverid data should not be readily correlated with
The identifer returned via an "ID.SERVER." query SHOULD NOT contain a hostname or unicast IP address that may be considered private to
the hostname or other information that could be considered sensitive. the nameserver operator's management infrastructure.
Acknowledgements
The technique for host identification documented here derive from Propagation of protocol or service meta-data can sometimes expose the
practices implemented by Paul Vixie of the Internet Software application to denial of service or other attack. As DNS is a
Consortium in the Berkeley Internet Name Domain package. Useful critically important infrastructure service for the production
comments on earlier drafts were provided by Bob Halley, Brian Internet, extra care needs to be taken against this risk for
Wellington, Andreas Gustafsson, Ted Hardie, Chris Yarnell, and designers, implementors, and operators of a new mechanism for server
members of the ICANN Root Server System Advisory Council. Additional identification.
explanatory information provided due to questions received from Randy
Bush.
References 7. Acknowledgements
[RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", The technique for host identification documented here was initially
RFC 1034, November 1987. implemented by Paul Vixie of the Internet Software Consortium in the
Berkeley Internet Name Daemon package. 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 Committee. The newest draft takes
a significantly different direction from previous versions, owing to
discussion among contributors to the DNSOP working group and others,
particularly Olafur Gudmundsson, Ed Lewis, Bill Manning, Sam Weiler,
and Rob Austein.
[RFC1035] Mockapetris, P., "Domain Names - Implementation and Intellectual Property Statement
Specifications", RFC 1035, November 1987.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate The IETF takes no position regarding the validity or scope of any
Requirement Levels", BCP 14, RFC 2119, March 1997. Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
[RFC3258] Hardie, T., "Distributing Authoritative Name Servers via Copies of IPR disclosures made to the IETF Secretariat and any
Shared Unicast Addresses", RFC 3258, April, 2002. assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
Author's Address The IETF invites any interested party to bring to its attention any
David Conrad copyrights, patents or patent applications, or other proprietary
Nominum, Inc. rights that may cover technology that may be required to implement
2385 Bay Road this standard. Please address the information to the IETF at
Redwood City, CA 94063 ietf-ipr@ietf.org.
USA
Phone: +1 650 381 6003 Disclaimer of Validity
Fax: +1 650 381 6055
Email: david.conrad@nominum.com
Full Copyright Statement This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright (C) The Internet Society (2000). All Rights Reserved. Copyright Statement
This document and translations of it may be copied and furnished to Copyright (C) The Internet Society (2004). This document is subject
others, and derivative works that comment on or otherwise explain it to the rights, licenses and restrictions contained in BCP 78, and
or assist in its implementation may be prepared, copied, published and except as set forth therein, the authors retain all their rights.
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be Acknowledgment
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an Funding for the RFC Editor function is currently provided by the
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING Internet Society.
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE."
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/