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).
AbstractWith 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.
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. 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 BIND within the CHAOS class "BIND." domain is "VERSION.BIND.". A query for a CHAOS TXT RR for this name will return an
administratively defined string which defaults to the software version of the server responding. This is, however, not generally implemented by other vendors.) 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. The initial and still common form, using "BIND.", is implementation specific. BIND is one DNS implementation. At the time of this writing, it is probably 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 aforementioned refinement changes the query label but preserves the ad hoc CHAOS/TXT mechanism. 4. There is no convention or shared understanding of what information an answer to such a query for a server identity could or should contain, including a possible encoding or authentication mechanism. 5. Hypothetically, since DNSSEC has been defined to cover all DNS classes, the TXT RRs returned in response to the "ID.SERVER." query could be signed, which has the advantages described in [RFC4033]. However, since DNSSEC deployment for the CHAOS class is neither existent nor foreseeable, and since the "ID.SERVER." TXT RR is expected to be unique per server, this would be impossible in practice. The first of the listed disadvantages may be technically the most serious. It argues for an attempt to design a good answer to the problem, "I need to know what nameserver is answering my queries", not simply a convenient one.
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- public and considered sensitive by the operator, such as a hostname or unicast IP address maintained for administrative purposes. 5. It should be possible to authenticate the received data by some mechanism analogous to those provided by DNSSEC. In this context, the need could be met by including encryption options in the specification of a new mechanism. 6. The identification mechanism should not be implementation- specific. NSID], including relevant IANA action.
Both authentication and confidentiality of server identification data are potentially of interest to administrators -- that is, operators may wish to make such data available and reliable to themselves and their chosen associates only. This constraint would imply both an ability to authenticate it to themselves and to keep it private from arbitrary other parties, which leads to characteristics 4 and 5 of an improved solution. [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", STD 13, RFC 1034, November 1987. [RFC1035] Mockapetris, P., "Domain Names - Implementation and Specification", STD 13, RFC 1035, November 1987. [RFC3258] Hardie, T., "Distributing Authoritative Name Servers via Shared Unicast Addresses", RFC 3258, April 2002. [BIND] ISC, "BIND 9 Configuration Reference". [NSID] Austein, R., "DNS Name Server Identifier Option (NSID)", Work in Progress, June 2006. [RFC4033] Arends, R., Austein, R., Larson, M., Massey, D., and S. Rose, "DNS Security Introduction and Requirements", RFC 4033, March 2005.
http://www.isc.org/ David Conrad ICANN 4676 Admiralty Way Marina del Rey, CA 90292 US Phone: +1 310 823 9358 EMail: email@example.com URI: http://www.iana.org/
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