Network Working Group S. Woolf Internet-Draft Internet Systems Consortium, Inc. Expires:
September 14, 2005April 30, 2006 D. Conrad Nominum, Inc. March 13,October 27, 2005 Requirements for a Mechanism Identifying an Authoritativea Name Server draft-ietf-dnsop-serverid-04Instance draft-ietf-dnsop-serverid-05 Status of this Memo 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 becomebecomes aware will be disclosed, in accordance with RFC 3668.Section 6 of BCP 79. 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.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 Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 14, 2005.April 30, 2006. Copyright Notice Copyright (C) The Internet Society (2005). 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.aid for administrators. 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 disadvantages, and to characterize an improved mechanism. 1. Introduction 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 identificationhave 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 onesome widely deployed implementationimplementations of the DNS protocolprotocol, including advantages and disadvantages, and discusses requirements forsome attributes of an improved solution to the problem. 2.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. 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, and some changes in management practices as the public Internet has evolved, 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 (such as those generated by tools such aslike "traceroute"), etc., can end up going to a different server than that 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-uniquepossibly-non- unique "server that answered my 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. 3.2. Existing Conventions Recent versions of the commonly deployed Berkeley Internet Name Domain implementation of the DNS protocol suite from the Internet SoftwareSystems Consortium [BIND] support a way of identifying a particular server via the use of a standard,standards-compliant, 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. ForA 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 query for a TXT RR for this name will return an administratively defined string which defaults to the version of the server responding. This is, however, not generally implemented by other vendors. 3.1vendors.) 2.1. Advantages There are several valuable attributes to this mechanism, which account for its usefulness. 1. The "hostname.bind" or "server.id" query response 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. Since the identity information is requested and returned within the DNS protocol, it doesn't require allowing any other query mechanism to the server, such as holes in firewalls for otherwise-unallowed ICMP Echo requests. Thus it does not require any special exceptions to site security policy. 3. It is simple to configure. An administrator can easily turn on this feature and control the results of the relevant query. 4. 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. 3.22.2. Disadvantages At the same time, there are some forbiddingserious drawbacks to the VERSION.BINDCHAOS/TXT query 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. ItThe initial and still common form, using .BIND, is implementation specific. BIND is one DNS implementation. At the time of this writing, it is probably the most prevalent for authoritative 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 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. 4.3. Characteristics of an Implementation Neutral Convention 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. 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 other reserved values outside of the existing protocol mechanisms for these, i.e. the OPT pseudo-RR. In particular, it should not propagate the existing drawback of requiring support for a CLASS and top level domain in the authoritative server (or the querying tool) to be useful. 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-publicnon- 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. 5.implementation- specific. 4. IANA Considerations 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. 6.5. Security Considerations Providing identifying information as to which server is responding to a particular query from a particular location in the Internet 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. 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. 7.6. Acknowledgements 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 version 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. Authors' Addresses Suzanne Woolf Internet Systems Consortium, Inc. 950 Charter Street Redwood City, CA 94063 US Phone: +1 650 423-1333 Email: firstname.lastname@example.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: email@example.com URI: http://www.nominum.com/ Intellectual Property Statement 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. 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