draft-ietf-dnsop-serverid-04.txt   draft-ietf-dnsop-serverid-05.txt 
Network Working Group S. Woolf Network Working Group S. Woolf
Internet-Draft Internet Systems Consortium, Inc. Internet-Draft Internet Systems Consortium, Inc.
Expires: September 14, 2005 D. Conrad Expires: April 30, 2006 D. Conrad
Nominum, Inc. Nominum, Inc.
March 13, 2005 October 27, 2005
Identifying an Authoritative Name Server Requirements for a Mechanism Identifying a Name Server Instance
draft-ietf-dnsop-serverid-04 draft-ietf-dnsop-serverid-05
Status of this Memo Status of this Memo
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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 Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
With the increased use of DNS anycast, load balancing, and other With the increased use of DNS anycast, load balancing, and other
mechanisms allowing more than one DNS name server to share a single 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 IP address, it is sometimes difficult to tell which of a pool of name
servers has answered a particular query. A standardized mechanism to servers has answered a particular query. A standardized mechanism to
determine the identity of a name server responding to a particular determine the identity of a name server responding to a particular
query would be useful, particularly as a diagnostic aid. Existing ad query would be useful, particularly as a diagnostic aid for
hoc mechanisms for addressing this concern are not adequate. This administrators. Existing ad hoc mechanisms for addressing this
document attempts to describe the common ad hoc solution to this concern have some shortcomings, not the least of which is the lack of
problem, including its advantages and disadvantages, and to prior analysis of exactly how such a mechanism should be designed and
characterize an improved mechanism. deployed. This document describes the existing convention used in
some widely deployed implementations of the DNS protocol, including
1. Introduction advantages and disadvantages, and discusses some attributes of an
improved mechanism.
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.
Unfortunately, existing ad-hoc mechanisms for providing such
identification 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 one widely deployed implementation of the DNS
protocol and discusses requirements for an improved solution to the
problem.
2. Rationale 1. Introduction and 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. This is most obviously useful for authoritative
has become more problematic due the deployment of various load nameservers in the attempt to diagnose the source or prevalence of
balancing solutions, including the use of shared unicast addresses as inaccurate data, but can also conceivably be useful for caching
resolvers. 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]. documented in [RFC3258].
An unfortunate side effect of these load balancing solutions, and An unfortunate side effect of these load balancing solutions, and
some changes in management practices as the public Internet has some changes in management practices as the public Internet has
evolved, is that traditional methods of determining which server is evolved, is that traditional methods of determining which server is
responding can be unreliable. Specifically, non-DNS methods such as responding can be unreliable. Specifically, non-DNS methods such as
ICMP ping, TCP connections, or non-DNS UDP packets (such as those ICMP ping, TCP connections, or non-DNS UDP packets (such as those
generated by tools such as "traceroute"), etc., can end up going to a generated by tools like "traceroute"), etc., can end up going to a
different server than that which receives the DNS queries. different server than that which receives the DNS queries.
There is a well-known and frequently-used technique for determining There is a well-known and frequently-used technique for determining
an identity for a nameserver more specific than the an identity for a nameserver more specific than the possibly-non-
possibly-non-unique "server that answered my query". The widespread unique "server that answered my query". The widespread use of the
use of the existing convention suggests a need for a documented, existing convention suggests a need for a documented, interoperable
interoperable means of querying the identity of a nameserver that may means of querying the identity of a nameserver that may be part of an
be part of an anycast or load-balancing cluster. At the same time, anycast or load-balancing cluster. At the same time, however, it
however, it also has some drawbacks that argue against standardizing also has some drawbacks that argue against standardizing it as it's
it as it's been practiced so far. been practiced so far.
3. Existing Conventions 2. 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 Systems 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 standards-compliant, if somewhat unusual, DNS
Specifically, a query to a late model BIND server for a TXT resource query. Specifically, a query to a late model BIND server for a TXT
record in class 3 (CHAOS) for the domain name "HOSTNAME.BIND." will resource record in class 3 (CHAOS) for the domain name
return a string that can be configured by the name server "HOSTNAME.BIND." will return a string that can be configured by the
administrator to provide a unique identifier for the responding name server administrator to provide a unique identifier for the
server (defaulting to the value of a gethostname() call). This responding server (defaulting to the value of a gethostname() call).
mechanism, which is an extension of the BIND convention of using 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 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 A refinement to this, which dropped the implementation-specific
string, replaces ".BIND" with ".ID". Thus the query string to learn
the unique name of a server may be queried as "SERVER.ID".
(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 query for a TXT RR for this name will return an administratively
defined string which defaults to the version of the server defined string which defaults to the version of the server
responding. This is, however, not generally implemented by other responding. This is, however, not generally implemented by other
vendors. vendors.)
3.1 Advantages 2.1. Advantages
There are several valuable attributes to this mechanism, which There are several valuable attributes to this mechanism, which
account for its usefulness. account for its usefulness.
1. The "hostname.bind" query response mechanism is within the DNS
protocol itself. An identification mechanism that relies on the 1. The "hostname.bind" or "server.id" query response mechanism is
DNS protocol is more likely to be successful (although not within the DNS protocol itself. An identification mechanism that
guaranteed) in going to the same machine as a "normal" DNS query. 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. Since the identity information is requested and returned within 2. Since the identity information is requested and returned within
the DNS protocol, it doesn't require allowing any other query the DNS protocol, it doesn't require allowing any other query
mechanism to the server, such as holes in firewalls for mechanism to the server, such as holes in firewalls for
otherwise-unallowed ICMP Echo requests. Thus it does not require otherwise-unallowed ICMP Echo requests. Thus it does not require
any special exceptions to site security policy. any special exceptions to site security policy.
3. It is simple to configure. An administrator can easily turn on 3. It is simple to configure. An administrator can easily turn on
this feature and control the results of the relevant query. this feature and control the results of the relevant query.
4. It allows the administrator complete control of what information 4. It allows the administrator complete control of what information
is given out in the response, minimizing passive leakage of is given out in the response, minimizing passive leakage of
implementation or configuration details. Such details are often implementation or configuration details. Such details are often
considered sensitive by infrastructure operators. considered sensitive by infrastructure operators.
3.2 Disadvantages 2.2. Disadvantages
At the same time, there are some forbidding drawbacks to the At the same time, there are some serious drawbacks to the CHAOS/TXT
VERSION.BIND mechanism that argue against standardizing it as it query mechanism that argue against standardizing it as it currently
currently operates. operates.
1. It requires an additional query to correlate between the answer 1. It requires an additional query to correlate between the answer
to a DNS query under normal conditions and the supposed identity to a DNS query under normal conditions and the supposed identity
of the server receiving the query. There are a number of of the server receiving the query. There are a number of
situations in which this simply isn't reliable. situations in which this simply isn't reliable.
2. It reserves an entire class in the DNS (CHAOS) for what amounts 2. It reserves an entire class in the DNS (CHAOS) for what amounts
to one zone. While CHAOS class is defined in [RFC1034] and to one zone. While CHAOS class is defined in [RFC1034] and
[RFC1035], it's not clear that supporting it solely for this [RFC1035], it's not clear that supporting it solely for this
purpose is a good use of the namespace or of implementation purpose is a good use of the namespace or of implementation
effort. effort.
3. It is implementation specific. BIND is one DNS implementation.
At the time of this writing, it is probably the most prevalent 3. The initial and still common form, using .BIND, is implementation
for authoritative servers. This does not justify standardizing specific. BIND is one DNS implementation. At the time of this
on its ad hoc solution to a problem shared across many operators writing, it is probably the most prevalent for authoritative
and implementors. servers. This does not justify standardizing on its ad hoc
solution to a problem shared across many operators and
implementors. Meanwhile, the proposed refinement changes the
string but preserves the ad hoc CHAOS/TXT mechanism.
There is no convention or shared understanding of what information an
answer to such a query for a server identity could or should include,
including a possible encoding or authentication mechanism.
The first of the listed disadvantages is technically the most The first of the listed disadvantages is technically the most
serious. It argues for an attempt to design a good answer to the serious. It argues for an attempt to design a good answer to the
problem that "I need to know what nameserver is answering my problem that "I need to know what nameserver is answering my
queries", not simply a convenient one. queries", not simply a convenient one.
4. Characteristics of an Implementation Neutral Convention 3. Characteristics of an Implementation Neutral Convention
The discussion above of advantages and disadvantages to the The discussion above of advantages and disadvantages to the
HOSTNAME.BIND mechanism suggest some requirements for a better HOSTNAME.BIND mechanism suggest some requirements for a better
solution to the server identification problem. These are summarized solution to the server identification problem. These are summarized
here as guidelines for any effort to provide appropriate protocol here as guidelines for any effort to provide appropriate protocol
extensions: extensions:
1. The mechanism adopted MUST be in-band for the DNS protocol. That 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 is, it needs to allow the query for the server's identifying
information to be part of a normal, operational query. It SHOULD information to be part of a normal, operational query. It SHOULD
also permit a separate, dedicated query for the server's also permit a separate, dedicated query for the server's
identifying information. identifying information. But it should preserve the ability of
the CHAOS/TXT query-based mechanism to work through firewalls and
in other situations where only DNS can be relied upon to reach
the server of interest.
2. The new mechanism SHOULD not require dedicated namespaces or 2. The new mechanism SHOULD not require dedicated namespaces or
other reserved values outside of the existing protocol mechanisms other reserved values outside of the existing protocol mechanisms
for these, i.e. the OPT pseudo-RR. In particular, it should not for these, i.e. the OPT pseudo-RR. In particular, it should not
propagate the existing drawback of requiring support for a CLASS propagate the existing drawback of requiring support for a CLASS
and top level domain in the authoritative server (or the querying and top level domain in the authoritative server (or the querying
tool) to be useful. tool) to be useful.
3. Support for the identification functionality SHOULD be easy to 3. Support for the identification functionality SHOULD be easy to
implement and easy to enable. It MUST be easy to disable and implement and easy to enable. It MUST be easy to disable and
SHOULD lend itself to access controls on who can query for it. 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 4. It should be possible to return a unique identifier for a server
without requiring the exposure of information that may be without requiring the exposure of information that may be non-
non-public and considered sensitive by the operator, such as a public and considered sensitive by the operator, such as a
hostname or unicast IP address maintained for administrative hostname or unicast IP address maintained for administrative
purposes. purposes.
5. The identification mechanism SHOULD NOT be
implementation-specific.
5. IANA Considerations 5. The identification mechanism SHOULD NOT be implementation-
specific.
4. IANA Considerations
This document proposes no specific IANA action. Protocol extensions, This document proposes no specific IANA action. Protocol extensions,
if any, to meet the requirements described are out of scope for this if any, to meet the requirements described are out of scope for this
document. Should such extensions be specified and adopted by normal document. Should such extensions be specified and adopted by normal
IETF process, the specification will include appropriate guidance to IETF process, the specification will include appropriate guidance to
IANA. IANA.
6. Security Considerations 5. Security Considerations
Providing identifying information as to which server is responding to Providing identifying information as to which server is responding to
a particular query from a particular location in the Internet can be a particular query from a particular location in the Internet can be
seen as information leakage and thus a security risk. This motivates seen as information leakage and thus a security risk. This motivates
the suggestion above that a new mechanism for server identification the suggestion above that a new mechanism for server identification
allow the administrator to disable the functionality altogether or allow the administrator to disable the functionality altogether or
partially restrict availability of the data. It also suggests that partially restrict availability of the data. It also suggests that
the serverid data should not be readily correlated with a hostname or the serverid data should not be readily correlated with a hostname or
unicast IP address that may be considered private to the nameserver unicast IP address that may be considered private to the nameserver
operator's management infrastructure. operator's management infrastructure.
Propagation of protocol or service meta-data can sometimes expose the Propagation of protocol or service meta-data can sometimes expose the
application to denial of service or other attack. As DNS is a application to denial of service or other attack. As DNS is a
critically important infrastructure service for the production critically important infrastructure service for the production
Internet, extra care needs to be taken against this risk for Internet, extra care needs to be taken against this risk for
designers, implementors, and operators of a new mechanism for server designers, implementors, and operators of a new mechanism for server
identification. identification.
7. Acknowledgements 6. Acknowledgements
The technique for host identification documented here was initially The technique for host identification documented here was initially
implemented by Paul Vixie of the Internet Software Consortium in the implemented by Paul Vixie of the Internet Software Consortium in the
Berkeley Internet Name Daemon package. Comments and questions on Berkeley Internet Name Daemon package. Comments and questions on
earlier drafts were provided by Bob Halley, Brian Wellington, Andreas earlier drafts were provided by Bob Halley, Brian Wellington, Andreas
Gustafsson, Ted Hardie, Chris Yarnell, Randy Bush, and members of the Gustafsson, Ted Hardie, Chris Yarnell, Randy Bush, and members of the
ICANN Root Server System Advisory Committee. The newest version ICANN Root Server System Advisory Committee. The newest version
takes a significantly different direction from previous versions, takes a significantly different direction from previous versions,
owing to discussion among contributors to the DNSOP working group and owing to discussion among contributors to the DNSOP working group and
others, particularly Olafur Gudmundsson, Ed Lewis, Bill Manning, Sam others, particularly Olafur Gudmundsson, Ed Lewis, Bill Manning, Sam
Weiler, and Rob Austein. Weiler, and Rob Austein.
Authors' Addresses
Suzanne Woolf
Internet Systems Consortium, Inc.
950 Charter Street
Redwood City, CA 94063
US
Phone: +1 650 423-1333
Email: woolf@isc.org
URI: http://www.isc.org/
David Conrad
Nominum, Inc.
2385 Bay Road
Redwood City, CA 94063
US
Phone: +1 1 650 381 6003
Email: david.conrad@nominum.com
URI: http://www.nominum.com/
Intellectual Property Statement Intellectual Property Statement
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Intellectual Property Rights or other rights that might be claimed to Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights 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 might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79. found in BCP 78 and BCP 79.
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