--- 1/draft-ietf-dnsop-serverid-01.txt 2006-02-04 23:14:20.000000000 +0100 +++ 2/draft-ietf-dnsop-serverid-02.txt 2006-02-04 23:14:20.000000000 +0100 @@ -1,229 +1,263 @@ -INTERNET-DRAFT David Conrad -draft-ietf-dnsop-serverid-01.txt Nominum, Inc. - November, 2002 +Network Working Group S. Woolf +Internet-Draft Internet Systems Consortium, Inc. +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 - This document is an Internet-Draft and is in full conformance with - all provisions of Section 10 of RFC2026. + This document is an Internet-Draft and is subject to all provisions + 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 Task Force (IETF), its areas, and its working groups. Note that - other groups may also distribute working documents as Internet- - Drafts. + other groups may also distribute working documents as + Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." - The list of current Internet-Drafts can be accessed at - http://www.ietf.org/ietf/1id-abstracts.txt + The list of current Internet-Drafts can be accessed at http:// + www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at 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 - A standardized mechanism to determine the identity of a name server - responding to a particular query would be useful, particularly as a - diagnostic aid. This document describes an identification convention - used in one widely deployed implementation of the DNS protocol and - proposes a slight modification to that convention aimed at addressing - some implementation concerns. + 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 attempts to describe the common ad hoc solution to this + problem, including its advantages and disadvantasges, and to + characterize an improved mechanism. 1. Introduction - Determining the identity of the name server responding to a query has - become more complex due primarily to the proliferation of various - load balancing techniques. This document describes a convention used - by one particular DNS server implementation to provide identifying - information and proposes a slight modification to that convention to - address concerns regarding implementation neutrality. + 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. - Note that this document makes no value judgements as to whether or - not the convention in current use is good or bad; it merely documents - the covention's existence and proposes a slight redefinition of the - convention to address non-technical implementation concerns. + 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 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 assumption that 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. + 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. -3. Historical Conventions +3. 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 responding. -4. An Implementation Neutral Convention - - 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" +3.1 Advantages - 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. - ID CH TXT "b" +3.2 Disadvantages - 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 - serving both "a.example.com" and "b.example.com" should return "a" or - "b" depending on which machine the query was routed. + The first of the listed disadvantages is technically the most + serious. It argues for an attempt to design a good answer to the + 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 - information. Implementors SHOULD provide a way to limit who can - query for the identifying information. +4. Characteristics of an Implementation Neutral Convention - The use of other names in the CHAOS class "SERVER." domain are beyond - the scope of this document. + The discussion above of advantages and disadvantages to the + 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 - and a registry should be created that reserves the "ID" name. In the - future, requests may be submitted for other sub-domains of "SERVER.", - e.g., "VERSION.SERVER." and the IANA should take appropriate action. + This document proposes no specific IANA action. Protocol extensions, + if any, to meet the requirements described are out of scope for this + document. Should such extensions be specified and adopted by normal + IETF process, the specification will include appropriate guidance to + IANA. -Security Considerations +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 to restrict who can query for the "ID.SERVER." domain. - Filtering on source address would be one way in which restrictions - can be applied. - - The identifer returned via an "ID.SERVER." query SHOULD NOT contain - the hostname or other information that could be considered sensitive. - -Acknowledgements + can be seen as information leakage and thus a security risk. This + motivates the suggestion above that a new mechanism for server + identification allow the administrator to disable the functionality + altogether or partially restrict availability of the data. It also + suggests that the serverid data should not be readily correlated with + a hostname or unicast IP address that may be considered private to + the nameserver operator's management infrastructure. - The technique for host identification documented here derive from - practices implemented by Paul Vixie of the Internet Software - Consortium in the Berkeley Internet Name Domain package. Useful - comments on earlier drafts were provided by Bob Halley, Brian - Wellington, Andreas Gustafsson, Ted Hardie, Chris Yarnell, and - members of the ICANN Root Server System Advisory Council. Additional - explanatory information provided due to questions received from Randy - Bush. + Propagation of protocol or service meta-data can sometimes expose the + application to denial of service or other attack. As DNS is a + critically important infrastructure service for the production + Internet, extra care needs to be taken against this risk for + designers, implementors, and operators of a new mechanism for server + identification. -References +7. Acknowledgements - [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", - RFC 1034, November 1987. + The technique for host identification documented here was initially + 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 - Specifications", RFC 1035, November 1987. +Intellectual Property Statement - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate - Requirement Levels", BCP 14, RFC 2119, March 1997. + The IETF takes no position regarding the validity or scope of any + 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 - Shared Unicast Addresses", RFC 3258, April, 2002. + Copies of IPR disclosures made to the IETF Secretariat and any + 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 - David Conrad - Nominum, Inc. - 2385 Bay Road - Redwood City, CA 94063 - USA + The IETF invites any interested party to bring to its attention any + copyrights, patents or patent applications, or other proprietary + rights that may cover technology that may be required to implement + this standard. Please address the information to the IETF at + ietf-ipr@ietf.org. - Phone: +1 650 381 6003 - Fax: +1 650 381 6055 - Email: david.conrad@nominum.com +Disclaimer of Validity -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). 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