Common Misbehavior Against DNS Queries for IPv6 Addresses
The information below is for an old version of the document that is already published as an RFC.
This is an older version of an Internet-Draft that was ultimately published as RFC 4074.
|Authors||Yasuhiro Orange Morishita , Tatsuya Jinmei|
|Last updated||2013-03-02 (Latest revision 2004-10-25)|
|RFC stream||Internet Engineering Task Force (IETF)|
|Additional resources||Mailing list discussion|
|IESG||IESG state||RFC 4074 (Informational)|
|Responsible AD||David Kessens|
|Send notices firstname.lastname@example.org, email@example.com|
IETF DNSOP Working Group Y. Morishita Internet-Draft JPRS Expires: April 23, 2005 T. Jinmei Toshiba October 23, 2004 Common Misbehavior against DNS Queries for IPv6 Addresses draft-ietf-dnsop-misbehavior-against-aaaa-02.txt 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 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. 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 April 23, 2005. Copyright Notice Copyright (C) The Internet Society (2004). Abstract There is some known misbehavior of DNS authoritative servers when they are queried for AAAA resource records. Such behavior can block IPv4 communication which should actually be available, cause a significant delay in name resolution, or even make a denial of service attack. This memo describes details of the known cases and discusses the effect of the cases. Morishita & Jinmei Expires April 23, 2005 [Page 1] Internet-Draft Common Misbehavior against AAAA Queries October 2004 1. Introduction Many existing DNS clients (resolvers) that support IPv6 first search for AAAA Resource Records (RRs) of a target host name, and then for A RRs of the same name. This fallback mechanism is based on the DNS specifications, which if not obeyed by authoritative servers can produce unpleasant results. In some cases, for example, a web browser fails to connect to a web server it could otherwise reach. In the following sections, this memo describes some typical cases of such misbehavior and its (bad) effects. Note that the misbehavior is not specific to AAAA RRs. In fact, all known examples also apply to the cases of queries for MX, NS, and SOA RRs. The authors even believe this can be generalized for all types of queries other than those for A RRs. In this memo, however, we concentrate on the case for AAAA queries, since the problem is particularly severe for resolvers that support IPv6, which thus affects many end users. Resolvers at end users normally send A and/or AAAA queries only, and so the problem for the other cases is relatively minor. 2. Network Model In this memo, we assume a typical network model of name resolution environment using DNS. It consists of three components; stub resolvers, caching servers, and authoritative servers. A stub resolver issues a recursive query to a caching server, which then handles the entire name resolution procedure recursively. The caching server caches the result of the query as well as sends the result to the stub resolver. The authoritative servers respond to queries for names for which they have the authority, normally in a non-recursive manner. 3. Expected Behavior Suppose that an authoritative server has an A RR but not a AAAA RR for a host name. Then the server should return a response to a query for a AAAA RR of the name with the response code (RCODE) being 0 (indicating no error) and with an empty answer section (see Sections 4.3.2 and 6.2.4 of ). Such a response indicates that there is at least one RR of a different type than AAAA for the queried name, and the stub resolver can then look for A RRs. This way, the caching server can cache the fact that the queried name does not have a AAAA RR (but may have other types of RRs), and thus can improve the response time to further queries for a AAAA RR of the name. Morishita & Jinmei Expires April 23, 2005 [Page 2] Internet-Draft Common Misbehavior against AAAA Queries October 2004 4. Problematic Behaviors There are some known cases at authoritative servers that do not conform to the expected behavior. This section describes those problematic cases. 4.1 Ignore Queries for AAAA Some authoritative servers seem to ignore queries for a AAAA RR, causing a delay at the stub resolver to fall back to a query for an A RR. This behavior may even cause a fatal timeout at the resolver or at the application which calls the resolver. Even if the resolver eventually falls back, the result can be an unacceptable delay for the application user, especially with interactive applications like web browsing. 4.2 Return "Name Error" This type of server returns a response with the RCODE being 3 ("Name Error") to a query for a AAAA RR, indicating it does not have any RRs of any type for the queried name. With this response, the stub resolver may immediately give up and never fall back. Even if the resolver retries with a query for an A RR, the negative response for the name has been cached in the caching server, and the caching server will simply return the negative response. As a result, the stub resolver considers this as a fatal error in name resolution. There have been several known examples of this behavior, but all the examples that the authors know have fixed their behavior as of this writing. 4.3 Return Other Erroneous Codes Other authoritative servers return a response with other erroneous response codes than RCODE 3 ("Name Error"). One well-known such RCODE is 4 ("Not Implemented"), indicating the servers do not support the requested type of query. These cases are less harmful than the previous one; if the stub resolver falls back to querying for an A RR, the caching server will process the query correctly and return an appropriate response. However, these can still cause a serious effect. There was an authoritative server implementation that returned RCODE 2 ("Server failure") to queries for AAAA RRs. One widely deployed mail server Morishita & Jinmei Expires April 23, 2005 [Page 3] Internet-Draft Common Misbehavior against AAAA Queries October 2004 implementation with a certain type of resolver library interpreted this result as an indication of retry and did not fall back to queries for A RRs, causing failure of message delivery. If the caching server receives a response with these response codes, it does not cache the fact that the queried name has no AAAA RR, resulting in redundant queries for AAAA RRs in the future. The behavior will waste network bandwidth and increase the load of the authoritative server. Using RCODE 1 ("Format error") would cause a similar effect, though the authors have not seen such implementations yet. 4.4 Return a Broken Response Another different type of authoritative servers returns broken responses to AAAA queries. A known behavior of this category is to return a response whose RR type is AAAA, but the length of the RDATA is 4 bytes. The 4-byte data looks like the IPv4 address of the queried host name. That is, the RR in the answer section would be described like this: www.bad.example. 600 IN AAAA 192.0.2.1 which is, of course, bogus (or at least meaningless). A widely deployed caching server implementation transparently returns the broken response (as well as caches it) to the stub resolver. Another known server implementation parses the response by themselves, and sends a separate response with the RCODE being 2 ("Server failure"). In either case, the broken response does not affect queries for an A RR of the same name. If the stub resolver falls back to A queries, it will get an appropriate response. The latter case, however, causes the same bad effect as that described in the previous section: redundant queries for AAAA RRs. 4.5 Make Lame Delegation Some authoritative servers respond to AAAA queries in a way causing lame delegation. In this case the parent zone specifies that the authoritative server should have the authority of a zone, but the server does not return an authoritative response for AAAA queries within the zone (i.e., the AA bit in the response is not set). On the other hand, the authoritative server returns an authoritative response for A queries. Morishita & Jinmei Expires April 23, 2005 [Page 4] Internet-Draft Common Misbehavior against AAAA Queries October 2004 When a caching server asks the server for AAAA RRs in the zone, it recognizes the delegation is lame, and returns a response with the RCODE being 2 ("Server failure") to the stub resolver. Furthermore, some caching servers record the authoritative server as lame for the zone and will not use it for a certain period of time. With this type of caching server, even if the stub resolver falls back to querying for an A RR, the caching server will simply return a response with the RCODE being 2, since all the servers are known to be "lame." There is also an implementation that relaxes the behavior a little bit. It basically tries to avoid using the lame server, but still continues to try it as a last resort. With this type of caching server, the stub resolver will get a correct response if it falls back after Sever failure. However, this still causes redundant AAAA queries as explained in the previous sections. 5. Security Considerations The CERT/CC pointed out that the response with RCODE 3 ("Name Error") described in Section 4.2 can be used for a denial of service attack . The same argument applies to the case of "lame delegation" described in Section 4.5 with a certain type of caching server. 6. Acknowledgements Erik Nordmark encouraged the authors to publish this document as an Internet Draft. Akira Kato and Paul Vixie reviewed a preliminary version of this document. Pekka Savola carefully reviewed a previous version and provided detailed comments. Bill Fenner, Scott Hollenbeck, Thomas Narten, and Alex Zinin reviewed and helped improve the document at the last stage for publication. 7 Informative References  Mockapetris, P., "DOMAIN NAMES - CONCEPTS AND FACILITIES", RFC 1034, November 1987.  The CERT Coordination Center, "Incorrect NXDOMAIN responses from AAAA queries could cause denial-of-service conditions", March 2003, <http://www.kb.cert.org/vuls/id/714121>. Morishita & Jinmei Expires April 23, 2005 [Page 5] Internet-Draft Common Misbehavior against AAAA Queries October 2004 Authors' Addresses MORISHITA Orange Yasuhiro Research and Development Department, Japan Registry Service Co.,Ltd. Chiyoda First Bldg. East 13F, 3-8-1 Nishi-Kanda Chiyoda-ku, Tokyo 101-0065 Japan EMail: firstname.lastname@example.org JINMEI Tatuya Corporate Research & Development Center, Toshiba Corporation 1 Komukai Toshiba-cho, Saiwai-ku Kawasaki-shi, Kanagawa 212-8582 Japan EMail: email@example.com Appendix A. Change History [NOTE TO RFC EDITOR: PLEASE REMOVE THIS SECTION UPON PUBLICATION.] Changes since draft-morishita-dnsop-misbehavior-against-aaaa-00 are: o Made a separate appendix and moved live examples to appendix so that we can remove them when this document is (ever) officially published. o Revised some live examples based on the recent status. o Noted in introduction that the misbehavior is not specific to AAAA and that this document still concentrates on the AAAA case. o Changed the section title of "delegation loop" to "lame delegation" in order to reflect the essential point of the issue. Wording on this matter was updated accordingly. o Updated the Acknowledgements list. o Changed the reference category from normative to informative (this is an informational document after all). o Changed the draft name to an IETF dnsop working group document (as agreed). o Applied several editorial fixes. Changes since draft-ietf-dnsop-misbehavior-against-aaaa-00 are: o Removed the appendix talking about live examples since these were not appropriate for official publication. o Added a note to rfc editor asking to remove this section upon publication. Morishita & Jinmei Expires April 23, 2005 [Page 6] Internet-Draft Common Misbehavior against AAAA Queries October 2004 Changes since draft-ietf-dnsop-misbehavior-against-aaaa-01 are: o Used the standard keywords for describing RCODEs. o Provided more specific references for RFC1034. o Described an additional known issue regarding RCODE 2 ("Server failure"). Also changed the section title accordingly. o Moved the "Ignore Queries" section to the first of Section 4, since it looks the most widely seen misbehavior. Morishita & Jinmei Expires April 23, 2005 [Page 7] Internet-Draft Common Misbehavior against AAAA Queries October 2004 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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